Is lightspeed really a limit?

We don’t (yet) have any way to test this, but University of Adelaide applied mathematicians are suggesting that an extended version of Einstein’s Theory of Special Relativity also holds true for velocities beyond lightspeed. One of the main predictions of Special Relativity is that the speed of light is treated as an absolute …

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1. Limits.

“'If you really don’t believe that faster-than-light is possible, then humans will be limited forever,' he said".

Humans might be limited anyway; after all, faster-than-light speeds might be impossible regardless of human beliefs.

1. Re: Limits - "Humans might be limited anyway".

True, but there's a big difference between 'might be' and 'will be', so it's worth suspending disbelief at least for a time.

I find it interesting and encouraging that something may come out of a false experimental result, simply because people were no longer quite so certain of the impossibility of FTL travel.

2. Re: Limits.

Of course there will be something that travels faster than light.

It's just that it has not been invented yet. Give it a couple of months and you'll see.

1. Re: Limits.

Yep, first it was the foot, then the horse, the train, the car, the aeroplane, the space rocket.

Humans keep going faster and faster, communication was shouting, smoke signals, lights, bean cans, telephone, wireless radio, fibre optics etc etc.

Someone will,invent it.

1. Re: Limits.

Why not suggest going below absolute zero as well (Hint : below absolute zero doesn't mean anything )

1. Re: Limits.

So several downvoters appear to believe that < absolute zero is a perfectly reasonable concept ?

Science education is appalling !

Absolute zero IS one of the limits - certainly in this universe

1. Re: Limits.

I don't think you were downvoted because people believe that there can be temperatures below absolute zero, but because you were drawing a comparison with a value which BY DEFINITION can only be zero or positive, whereas the limit of lightspeed exists because of a practicality relating to mass. There is no upper limit on temperature, by the way, so the analogy with speed fails there; of course you cannot have a speed below zero.

1. Re: Limits.

> I'll cling on to hope, thanks.

Do not hope to do impossible things. Hope to do feasible things. Anything else is religion in a terribly bad way.

This is the Slow Zone. Better accept it.

1. Re: Limits.@Destroy All Monsters

"Do not hope to do impossible things. Hope to do feasible things"

Aim low to ensure disappointment, then?

In seventy years we went from the Wright flyer limping a few yards through the air, to reaching the Moon, but you're suggesting that in essence we know it all now, and should stop anything other than unambitious incremental improvement.

I hope my descendants have more to look forward to than a lighter, more easily emptied vacuum cleaner.

1. Re: Limits.@Destroy All Monsters

When you put it like this, it saddens me greatly that this boom time of innovation came to an end nearly 40 Years ago now. Weren't we not meant to be colonizing Mars and live in floating houses (i.e. The Jetsons). And what about our flying Cars? If the Internet is the best thing to come out of our Epoch. Then may we be forgiven.

1. Re: Limits.@Destroy All Monsters

"Weren't we not meant to be colonizing Mars "

And NASA's budget was 5% of the US GDP.

But things have a way of sneaking up on people.

The question is do you want the *result* or the result by a specific *means*?

2. Re: Limits.

"This is the Slow Zone. Better accept it."

My mind bobbles :-)

2. Re: Limits.

I know it's by definition but it's amazing how many, otherwise intelligent well-educate people, think that it's just something that will be overcome as we learn more.

Incidently there may be a potentially max. temp. around 1E32K where physics breaks down so that all predictions fail.

1. Re: Limits.

@Chemist. I find this interesting:

http://www.wired.co.uk/news/archive/2012-09/20/warp-drives

"The drive works by using a wave to compress the spacetime in front of the spaceship while expanding the spacetime behind it. The ship itself would float in a "bubble" of normal spacetime that would float along the wave of compressed spacetime, like the way a surfer rides a break. The ship, inside the warp bubble, would apppear to be going faster than the speed of light relative to objects outside the bubble."

Now I'm no mathematician or physicist, but this seems to broadly concur with the Adelaide prof mentioned here?

1. Re: Limits.

"The drive works by using a wave to compress the spacetime"

Sorry this has nothing to do with it. The so-called warp drive even if it eventually proves feasible allows a ship moving less than c to travel large distances quickly by altering spacetime using exotic matter and a great deal of energy.

1. Re: Limits.

According to NASA at the Florida lab where a soccer ball sized field is being built,

the actual power needed to run the field is about 15 watts,

the power consumed currently by Voyager 1 and 2...

2. Re: Limits.

The limit question in Special Relativity is intrinsically more nuanced and interesting. Einstein assumed continuous increase in acceleration. Quantum physics gives us discreet increases. The equations still work if V > c and you assume the i is an indicator of (for lack of a better term) a phase shift. Which is what these mathematicians explored.

Would I ever want to be the test monkey in an experimental device based on these assumptions? Hell no! But it can be fun to talk about, even though Al's musings based on practicality are probably spot on.

3. Re: Limits.

" drawing a comparison with a value which BY DEFINITION "

Here's an experiment, you don' know anything about absolute zero, you have a good thermometer reading to low temperatures - doesn't matter what the scale reads in. You build various kinds of kit to produce lower and lower temps. At a certain point, to your amazement, the temperature doesn't go down anymore.

You have reached a limit - the same throughout the universe - we merely define that as 0 K.

In another universe with different parameters the limit will likely be different.

4. Re: Limits.

the limit of lightspeed exists because of a practicality relating to mass

Far more than that. Yes, there's a singularity in relativistic mass (and hence momentum, kinetic energy, etc) at C - but also in length and in time. And more importantly, FTL communication (which FTL travel implies) breaks causality.

In short, it's not just the infinite-energy requirement that makes C the universal speed limit.

2. Re: Limits.

I think you'll find the financial system is proof things existing below absolute zero.

1. Re: Limits.

@Tom7 that could also be the ideal argument for entropy :)

3. Re: Limits.

Rubbish, Chemist! Your poopy-head facts are just a temporary hindrance to my sci-fi fueled optimism!

First the speed of light will be broken, and your "absolute" zero will be shown up as positively balmy - Einstein said everything was relative after all, and he had a fine moustache. Then we'll move on to sub-planck length transistors and proving both P and not-P simultaneously.

The human race is unstoppable! So stick that in your sciency-wiency-pipe, divide it by zero and smoke it.

1. Re: Limits.

@Androgynous Cupboard

I do appreciate a well-reasoned argument. How about you provide one

4. Re: Limits.

< *absolute* zero sounds reasonable = V. poor science education.

*however* doubtful analogy.

Ambiguity is the enemy of uniform upvoting.

2. Re: Limits.

http://en.wikipedia.org/wiki/Negative_temperature

1. Re: Limits.

"http://en.wikipedia.org/wiki/Negative_temperature"

Now that you've found it try reading it and understanding what it actually means - here's a snipette :-

"by contrast a system with a truly negative temperature in absolute terms on the kelvin scale is hotter than any system with a positive temperature. If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system."

1. Re: Limits.

And I quote : "(Hint : below absolute zero doesn't mean anything )".

2. @Chemist

Funny, I understood what that wiki article is saying, and, ironically, this is because of my training as a chemist.

I think maybe a better comparison would be to say the temperature of an object cannot fall below absolute zero by passing though zero, principally because Heisenberg's uncertainty principle prevents anything from ever being at absolute zero.

To get to a temperature below absolute zero, a system has to have an upper bounded temperature, i.e. be a properly closed system with a finite number of states, when energy is pumped into such a system at the maximum temperature which is an asymptote, an inversion occurs, and the temperature becomes the minimum temperature of teh system, which is the negative of the abosulte maximum. This doesn't apply to everyday classical objects, but only to specific things, such as the energy states in the atoms comprising a laser, and similar quantum objects.

The speed of light is a similar system, as an object approaces the speed of light, its mass approaches infinity. it is not possible to be at the speed of light, as the mass, and therefore energy would be infinite, but it may be possible to be beyond the speed of light, in which case the object in question would have to have negative mass/energy. In fact theoretical particles travelling at beyond the speed of light would have a lower limit for their speed of c and negative mass. We are essentially cut off from such theoretical particles, since they cannot slow down beyond the speed of light, and we cannot speed up past that point; the problem being the point in time at which the velocity is at c.

1. Re: @Chemist

"but it may be possible to be beyond the speed of light, in which case the object in question would have to have negative mass/energy."

I point this out below somewhere although earlier in the day.

2. Re: @Chemist

What ?

maybe you're a chemist (?), but you ain't no physicist !!

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2. Re: @Chemist

Well I am really a chemist (retired) but I've spent a lot of my time writing scientific software, protein modelling and utilising quantum mechanics. All these things have required rather a good knowledge of physics..

Your evidence ?? and indeed provenance as you only joined today so we've not had the benefit of your wisdom before.

1. Re: @Chemist

I'm happy to believe you have a fine understanding of both physics and chemistry. Almost certainly better than mine. I've felt no need to down-vote you.

However when you make assertions along the lines of "science education is rubbish" you are kind of required to get your facts right thereafter.

You used as an example the fact that absolute zero is an absolute, and lower temperatures "have no meaning". I provided you with evidence that it does. Your response was to critcise me and assume I hadn't understood what I read. As it happens I believe I had understood it, and it told me your prior assertion was incorrect - negative temperatues do have meaning, albeit that meaning is rather esoteric by "normal" standards and is certainly not what the layman might consider "obvious".

High horses require high standards of their riders...

Not a boffin, just cold.

1. Re: @Chemist

I was actually replying to a comment by outinoregan who suggested that I didn't without giving any evidence.

As for the negative temperature as you say that's rather esoteric and not directly related to my point. I apologise if I assumed that you had no understanding of the area but on these forums many people know enough to search/quote from the web but have no real knowledge of the subject.

My comment about "science education being rubbish" was due to several comments recently in the media where several pronouncements were made along the lines of "of course everything is possible" when clearly the history of the world, let alone science shows that there are almost certainly limits in certain directions.

1. Re: @Chemist

Fair enough.

I confess I too despair of the standard of some reporting of science, and even more of what seems like a general malaise towards the subject as a whole. Although to be honest probability and risk are possibly an even bigger issue (from a maths graduate who does the lottery now and again - so who am I to talk!)

I don't know a great about the subject to be honest, but I do know what absolute zero is (cold :-)

I hope somebody works out how to go faster than light, preferably without requiring more energy than exists in the universe, but I don't expect to see it for anything larger than a electron in what remains of my lifetime, if even that.

As for everything being possible, well, we only have theories to support our scientific view of the world. Theories are far easier to prove wrong than correct. Point here is that some of the key theories we're talking about are proving incredibly robust. A certain amount of cynicism is always warranted, in both directions.

But as you say - there are limits - and we should always aim to make decisions based upon the best available evidence, not superstition, hope (see above) or too much star trek.

3. Re: @Chemist

I stopped reading when I saw the word 'asymptote' because it triggered a bad flashback. I'm feeling better now, thanks.

The speed of light is most obviously the ratio of time quantum to space quantum. Time and space are being created continuously (oops, I mean one quantum after the other, and quickly). With that in mind, you the readership might want to reconsider what is meant by 'at rest' and 'energy'.

4. Re: @Chemist

The problem to me seems to be what is the speed of light related to. Take a space craft traveling at almost the speed of light. Should a person on that craft be for example be watching a video and the screen in the tail and the person in the nose, would the picture never get to the viewer, yet he could walk to the TV as the body is on the same mass as the TV. (effectively just being a movable particle) or would he see the TV as normal so meaning that the speed of the light from the TV is actually travelling at "almost" 2 x the speed of light relative, well to what. Certainly not earth, because thats already clanking along at silly speeds.

1. Re: @Chemist

Suggest you read-up on this - the predictions are all very weird but many have been experimentally confirmed.

Wikipedia's Special Relativity is reasonable as is Time dilation

If you are on a craft at near c the light you measure ( from the TV or otherwise) will be measured as traveling at c - that's the cornerstone of SR - the observer will always measure light - ANY light - as traveling at c. To reconcile the problems that brings up other measurement s have to give way - in particular time varies.

This may all sound silly but experiments all agree. Sub-atomic particles with a known short lifetime last longer at high speed and do so by exactly the amount that SR predicts.

Further down this topic someone mentions that IF a craft could reach close to c the traveler inside could tour the galaxy in a short time by their measure although thousands of years might have passed on Earth

Incidently GR also predicts time changes due to gravity, the closer to a large mass the slower time runs - these effects are also measured as predicted.

It's a weird universe.

5. @Loyal Commenter

I think my brain just exploded.

3. Re: Limits.

"by contrast a system with a truly negative temperature in absolute terms on the kelvin scale is hotter than any system with a positive temperature. If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system."

So the temperature is a *ring*?

Which of course begs the question where does the *top* of the ring end and start going "negative"?

Bizarre.

2. Re: Limits. @ relpy

I dont think that falls into the 'laymans' language...

i,e, what is the closest 'black body' in the solar system???

:) hint, it is something that reflects NO light.. all the planets do.. :)

1. Re: Limits. @ relpy

Reflects *NO* Light.

Wouldn't want to be too hard on that.

find the right requency and I think it might.

Big and shiny not withstanding.

(icon because that's what it is)

(and okay, it reflects no light I grant you, to any measurable value of none).

3. Re: Limits.

Two different things: Absolute zero is not a thing, it is a lack of a thing, in this case, energy (the same goes for darkness.) FTL is something that would require more energy; infinite maybe, but it is derived from something, not nothing.

2. Re: Limits.

A shadow can travel (or be perceived to at any rate) faster than light. Not terribly functional mind.

1. Re: Limits.

A shadow does not "travel" in any sense a reasonable intelligence would accept. Neither does an equation, an idea or a train of thought.

Also, humans limited forever, no-go theorems, N is not NP, Gödel, the age of failed dreams (when we still watched the original Star Trek)

1. @Destroy All Monsters - "humans limited forever"

Bugger that!

If true, what's the point in carrying on? We might just as well use genetic engineering to cut our fertility down to a level that allows the human species to gracefully fade away, if we accept that there is no use for our intelligence.

I'll cling on to hope, thanks.

1. Re: @Destroy All Monsters - "humans limited forever"

"If true, what's the point in carrying on? We might just as well use genetic engineering to cut our fertility down to a level that allows the human species to gracefully fade away, if we accept that there is no use for our intelligence."

I think he probably meant faster than light travel was a no-go, not that there's no use for intelligence. There's more to life than clinging to some green-skinned space babe fantasy, mate. What that might be I don't know, but ...

2. Re: @Destroy All Monsters - "humans limited forever"

Even with relativity intact, you can get anywhere you like as fast as you want, (well, not counting pesky problems like getting bombarded with highly energetic particles caused by their relative blue-shift and the like). You just can't come back without massive time dilation. (See for example http://en.wikipedia.org/wiki/Twin_Paradox).

So, kindof hard to run a Galactic empire, but, hey maybe that's for the best.

1. Re: @Destroy All Monsters - "humans limited forever"

"you can get anywhere you like as fast as you want"

Assuming you have a means of generating the vast amount of energy required. - otherwise I agree

1. Re: @Destroy All Monsters - "humans limited forever"

"Assuming you have a means of generating the vast amount of energy required."

Generating the energy required is left as an exercise for the student.

3. Re: @Destroy All Monsters - "humans limited forever"

If true, what's the point in carrying on? We might just as well use genetic engineering to cut our fertility down to a level that allows the human species to gracefully fade away, if we accept that there is no use for our intelligence.

What a peculiar failure of imagination.

That there are things we can never do does not imply that there is nothing we can ever do. Even if we can never travel quickly to the stars, that doesn't mean there's no value in traveling to another country, or even to the next town over.

Life exists because the dissipation of an energy gradient created by the sun's radiation on the surface of the earth requires an increase in the information entropy of the system at that boundary, and we're one result of that. There's no great narrative of human existence that requires us to spread beyond our biosphere. What meaning exists in human life is the meaning we make from it. And we have never lacked for opportunities to do so.

1. Re: @Destroy All Monsters - "humans limited forever"

And furthermore, even if there is no FTL travel, that doesn't necessarily make it *impossible* for us to go to the stars, just difficult, and long. There are lots of possibilities for "hard" interstellar travel that don't require radical new physics: e.g. we could use genetic engineering to increase our life span, thereby making even a 50- or 100-year star trip feasible. We could do it via multi-generational "migration" trips. And in lieu of sending biological life, we could build A.I.s that could travel out there over the long centuries.

All the above are theoretically plausible, and given what we know, more plausible than FTL travel, even if we don't know how to do them yet. There's no _laws of physics_ that forbid them.

As for "spreading beyond the biosphere", no, it's not _required_, but I suspect that it'd be good for us if we didn't give up on our drive to _explore_ beyond it at least, even if it will take a long time to do so. And furthermore, we don't need even interstellar travel of any sort to "spread beyond the biosphere" -- setting up a base on the Moon would do. :)

Why go to space? Simple. We are opening up _new_ things, so that we can do _new_ stuff that has _never been done before_. It challenges us, and it is the logical continuation of our desire to know what's beyond the next hill and the next river. And we'll learn a lot doing it -- stuff that'll likely have many unseen benefits.

Though I'd think that for now, the issues on our planet are more pressing than going to the stars, but once we can overcome them, then, well, the stars seem like a logical next step.

2. Re: Limits.

"Also, humans limited forever, no-go theorems, N is not NP, Gödel, the age of failed dreams (when we still watched the original Star Trek)"

You assume "forever" will be like today.

Keep in mind 2 things.

Forever is a *long* time.

Remember what happens when you assume.

2. Re: Limits.

"A shadow can travel (or be perceived to at any rate) faster than light. Not terribly functional mind."

As can the spot of light from a rotating laser at sufficient radius - but it's not the same as FTL

3. Re: Limits.

Actually, shadows do travel at the speed of light.

3. Re: Limits.

----

Of course there will be something that travels faster than light.

It's just that it has not been invented yet. Give it a couple of months and you'll see.

----

Error correction for time relating to FTL travel; your statement should read:

------------------------------

Of course there will be something that travels faster than light.

It's just that it has not been invented yet. Give it a couple of months ago and it will have been.

(or something)

3. Re: Limits.

Still don't see these scientists point. Einstein was happy for you to go faster than light. You just had to exist as a faster than light particle first. You cannot accelerate things faster than light, because this requires infinite (or greater than infinite) energy.

The opposite applies to objects traveling faster than light AFAIK, you need infinite energy to slow them down.

That's where photons come in, you can't speed them up or slow then down. They always travel at "lightspeed".

Which leaves us with the final comment on the article. Faster than light might be possible, but unless the paper shows it's possible with energy less than infinite, it's all pointless. :(

1. Re: Limits.

They always travel at "lightspeed" for the medium through which they are travelling. Speed of light in a vacuum and all that.

2. Re: Limits.

"That's where photons come in, you can't speed them up or slow then down. They always travel at 'lightspeed'."

While it's true that photons travel at light speed. It is not true that they only travel at "c." Light is slowed down all the time. For example, refraction is the slowing of photons. Scientists have also devised all sorts of neat ways of slowing down photons to a walking speed.

1. Re: Limits.

Light is not slowed down. You either make it take a less direct route (gravity etc) or destroy it (absorption?) and re emit it. It's the time between being absorbed and re-emitted by electrons (IIRC) that takes the time, not the travel of the light wave.

Gravity does actually slow light down. But that's probably not a correct description. Gravity slows the universe down, so from our reference frame, I guess it's the same. :P

2. Re: Limits.

I think you'll find photons *always* travel at the lightspeed of the *medium* they are traveling in.

That fact that is slower than the one you are in kind of demonstrates the whole frames-of-reference thing quite neatly.

4. Re: Limits.

Einstein never said nothing can move faster than light. Teslar specifically stated that neutrons seem to exhibit faster then the speed of light speeds at high energy levels, nothing in e=mc2 prevents it from doing so. So please let's stick to the mathematical and physical facts, not assumptions that fit our current theories. "The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane." N. Teslar. Rember the sound barrier? Scientists actually argued it wasn't possible to break that barrier, light speed is no in the same league, but you can see how delusional mainstream science can be. "The scientists who appeared to have found in September that certain subatomic particles can travel faster than light have ruled out one potential source of error in their measurements after completing a second, fine-tuned version of their experiment.

Their results, posted on the ArXiv preprint server on Friday morning and submitted for peer review in the Journal of High Energy Physics, confirmed earlier measurements that neutrinos, sent through the ground from Cern near Geneva to the Gran Sasso lab in Italy 450 miles (720km) away seemed to travel faster than light."

5. Re: Limits.

Why is it that everyone conveniently forgets about things like time dilation and length contraction when they start speaking about speed limits? Is it that difficult to remember that as you go faster the distance traveled is shorter and the time it takes becomes longer? I know, it's a pisser, the faster you go the slower it seems and there's nothing to stop you from breaking the speed of light other than the fact that you couldn't tell because the only way to measure the speed is with something in an external reference frame and the signals travel at, wait for it, the speed of light.

1. Re: Limits.

The faster you go, the slower it seems, to AN EXTERNAL OBSERVER, to you, you just go faster. Yes, and things get thinner relative to you, and external time speeds up, and in the other reference frame, you get heavier . And visible light turns to X-rays, I like how people forget that. Absent some serious field tech, the main problem is the stuff you are flying through, oh and going home, you don't get to do that.

1. Re: Limits.

You forgot. While you keep going "faster", the universe continues to speed up too! Thus, you get to your destination not quicker, but slower.

For example, moving to Planet Zog 2 light years away, you speed up at 2x the speed of light, expecting to get there in 1 year. Nope, you experience 1 year (you actually did go faster) but when you get there, you missed the welcome party, it was 1 year ago, because 2 years still passed on Zog. :P

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2. Re: Limits.

"Is it that difficult to remember that as you go faster the distance traveled is shorter and the time it takes becomes longer?"

Yeah, no. If I take off for Proxima Centauri at 0.9c the trip doesn't "take longer." Time dilation and length contraction for me means that the trip is shorter in time and space. For the outside observer my length contracts by the Lorentz factor as well, but that's trivial in the grand scheme of things. Bottom line is that for me the trip to PC takes less than the 4.24/.9=4.7 years that you Earthers observe. It's more like 2 years in my shipboard time.

What prevents you from breaking --or more accurately going-- the speed of light is that your mass would be infinite and the energy required to get you to that speed would also be infinite. If you can avoid the singularity right at the speed of light then at least the equations don't go bang, but I don't know what imaginary mass means.

2. Then divide by the number you first thought of

It helps that mathematics keeps working with negative numbers and you can conveniently step over any divide by zero's. Unfortunately nature is not so kind.

1. Re: Then divide by the number you first thought of

Technically you can't divide by a value less than one, it's just a convenience mathematicians invented to save them having to rearrange the equation.

1. Re: Then divide by the number you first thought of

"Technically you can't divide by a value less than one" my ghostly pale hairless ass. Consider the humble case of the orange, and a segment, 1/8th (0.125x) the size of the whole.

1 / (0.125) = 8, which is the equivalent impenetrable mathematical moon-speak of asking: "How many 1/8ths of an orange are in a whole orange?" why, there would, naturally, be 8 fine sir.

1. Re: Then divide by the number you first thought of

""Technically you can't divide by a value less than one" my ghostly pale hairless ass. Consider the humble case of the orange, and a segment, 1/8th (0.125x) the size of the whole.

1 / (0.125) = 8, which is the equivalent impenetrable mathematical moon-speak of asking: "How many 1/8ths of an orange are in a whole orange?" why, there would, naturally, be 8 fine sir."

But you are not dividing, you are multiplying.

The division by a number less than 1 is a multiplication, but for algebraic simplicity it is 'allowed'.

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2. @ "But you are not dividing, you are multiplying."

"The division by a number less than 1 is a multiplication, but for algebraic simplicity it is 'allowed'."

Your ideas have some validity. You could divide the real numbers into two sets, and define division s.t. the divisor can only come from one set, while retaining the reciprocal theorem that each number in one set has a partner in the other set (such that the product is exactly one). You would have, as required, that division by numbers less than one isn't defined, but multiplication by their reciprocals is. This theory would encompass any arithmetic statement you'd ever want to make, and allow you to perform any practical calculation, so it is on the surface just as useful or valid as traditional arithmetic.

But, you would quickly end up finding the trivial proof that you can extend your concept of division in a well-defined way to include numbers less than one. You'd realize that if you did this, a lot of your earlier proofs would be half as long, and your calculations would be easier. The natural inclination would then be to simplify your entire theory to get rid of the two sets, unifying them into one set which you might call a Field.

So, if by "algebraic [sic] simplicity" you mean "it creates a fundamental and profound symmetry between numbers either side of one which gives our arithmetic techniques approximately double their power", then yes, you're right.

But more importantly, your tacit claim that other people's concept of this is not accepted mathematics, while your concept of this is accepted mathematics, is hilariously incorrect.

3. Re: Then divide by the number you first thought of

"The division by a number less than 1 is a multiplication, but for algebraic simplicity it is 'allowed'."

Can I multiply by a number less that one? Yes - but it's exactly the same as dividing by a number greater than one. So, by your argument, the multiplication by a number less than one is a division, but for algebraic simiplicity it is "allowed".

So, according to you, we can't multiply OR divide numbers less than one. Go figure.

2. Re: Then divide by the number you first thought of

You can divide by a number less than one. Say, 0.5. Perhaps you meant negative numbers? ;)

(This is also possible, happens all the time with debt!)

3. Re: Then divide by the number you first thought of

OK, so what is division? Division is asking how many of one number would be needed to make up another. For example, how many of these slivers of cake make up this whole cake?

The scale of the number range is mathematically meaningless.

For example, draw a circle and draw a couple of lines from the centre to two points near each other on the edge (creating a Sector, sometimes called a Slice in a Pie chart). You can calculate how many of these Sectors are in the whole circle by dividing the circle's circumference by the length of the arc describing the sector (the length of the arc is the distance between the points on the circumference). It doesn't matter if you describe the circumference of the circle as 1 metre, 3.3 linguines or 1000 mm as long as you measure the arc in the same units. In this case if the circumference was 1 metre and the arc was 0.125 metre then you are dividing by a number less than 1 - how is this technically impossible? If instead you recorded the measurement as 1000mm and the arc as 125mm the end result would be the same.

1. Re: Then divide by the number you first thought of

"God created the integers, all the rest is the work of Man." - Leopold Kronecker

3. wow that graph

That graph looks like some neo-nerd art. I dub it Graphism. Just print it up, and post it in an art museum probably would fetch more money than he gets paid as a physicist ;)

1. Re: wow that graph... Peter Maxx

Peter Max and those 1970's bed linens come to mind, hahaha. And, a live action cartoon show of the 70's does, too.

http://www.petermax.com/

2. Re: wow that graph

That's going on a t-shirt!

3. Re: wow that graph

I'll wait for the XKCD version...

4. Re: wow that graph

"To clear up a confusion regarding the labelling of the image...."

Well, now it's all crystal clear!

*looks at pretty lines and shading*

Yup... that's maths alright!

4. Only c is forbidden?

I thought that only the speed of light was forbidden to anything with mass. Isn't the problem that crossing that speed in either direction requires dividing by zero?

5. The zone labels on the graph are confusing me

What is 'U'? Is it the apparent relative velocity between observers? If it is then it was foolish to call it 'U' given that 'u' is used as the velocity of one of the observers.

6. Point of order (hopefully an interesting one). C is not the speed of light - it is the speed that anything with zero rest-mass will travel at - i.e. light is one of the class of things that travel at C.

1. Furthermore ...

'c', the speed of light, is the speed at which light _must_ travel at. If you use Maxwell's equations to analyse a self sustaining EM wave (e.g. light) then it's velocity can only be a value determined by the permeability and permittivity of the medium in which it exists. For free space, this is 'c', so if the characteristics of free space change, then the speed of light will change.

This classical analysis yields the value of 'c' and is easy enough to understand. How we got from there to Special Relativity, etc, is something that makes my brain hurt.

1. Perhaps I have a strange head then....

...I found the mathematics of Maxwell's equations extremely hard, and never did quite convince myself of them. However, the maths of Special Relativity, and the concepts behind it, just seems quite straight-forward (albeit non-intuitive).

Recommendation - Relativity and Common Sense by Hermann Bondi - recommended to me when I was in the 6th form by my Physics teacher. Made it crystal clear to me.

1. Re: Perhaps I have a strange head then....

Faster than a speeding comment:

A quick Google search got me an e-book version from archive.org. I'm not sure if this is legit, but I'll read it anyway. Thank you :)

2. Re: Furthermore ...

Not our fault. The "speed of light" is not always the same as "the maximum speed of the universe" which is usually the same as "the maximum speed of massless particles". :P

7. It's my understanding.....

that nothing in SR forbids FTL - just that approaching c from either direction requires infinite energy for anything with non-zero mass. It does, however, hint that anything that is traveling at c+ is a very strange beast indeed

1. Re: It's my understanding.....

That's as I remember it too... I think the idea that the math can work for speeds *above* c, only it's impossible to go *at* c, was already well-known.

1. Re: It's my understanding.....

Regular SR has a divide-by-zero if v=c, and gives imaginary/complex results (square root of a negative number) if v>c.

It's not hard to see they could find an equation which collapses onto normal SR in certain cases, just as SR collapses into normal Newtonian equations at low velocity. But you can find any number of equations that work, without them meaning anything.

1. Re: It's my understanding.....

Yep, I guess the "negative number" would be not only your body and vital organs being flipped inside out by going faster than light, but also your mass and energy going negative. A complete upside down to your laws of physics. So an experiment most teenagers would love to see tried!

1. Re: It's my understanding.....

"Yep, I guess the "negative number" would be not only your body and vital organs being flipped inside out by going faster than light, but also your mass and energy going negative. A complete upside down to your laws of physics. So an experiment most teenagers would love to see tried!"

Total protonic reversal. That would be bad.

2. Re: It's my understanding.....

... and therefore it is impossible to cross the boundary.

Who knows maybe all the dark matter, and weakly interacting massive particles are just those strange beasts zapping by at speeds greater then light, having discussions on their version of the register discussing the possibility of STL travel (slower then light ), and laughing at the ridiculous idea of anything moving slower then light, which would mean you could actually see where you were going before you got there, violating all kinds of conversion rules.

Just as we found that non-euclidean geometry would make mathematical sense, someone with better math skills then me could try and come up with a physics for the FTL world.

Who knows, maybe all the spooky action at a distance and the 2-slots, multiple world interpretation can be solved by just assuming a duality where we have an STL universe (ours) and an FTl universe (theirs) and all the quantum machanic weirdness is just the folks from the other side trying to get a message across

(or maybe it's just interference caused by their version of the X-factor TV shows)

Man I need more coffee ...

3. Re: It's my understanding.....

I think there was a theory that if you spent less than Planck time at the speed of light, you could accelerate past it - would require absurd amounts of energy though, and there's probably a number of other reasons why it can't be done.

2. Re: It's my understanding.....

"anything that is traveling at c+ is a very strange beast indeed"

But so it would appear to a chemist? However, my A level physics doesn't help me much here either.

So what happens when my ship coasting through deep space at c -2mph applies some additional thrust? Where does the energy from the increased thrust disappear to?

If my maths is correct, then to accerate 1 kg to marginally over c, then using Newtonian maths that's around 45 peta joules, or about the energy in one and a quarter million tonnes of coal. That's not infinite, so exactly when and how do those large, but very finite numbers become infinite?

1. Re: It's my understanding.....

That's because 'your' maths isn't valid. This isn't linear that's the whole point. I suggest you read a little SR

To get 1kg to 0.99c needs ~5E17 J

To get 1kg to 0.999c needs ~2E18J

To get 1kg to 0.99999c needs ~2E19J

as v->c , energy -> infinite

Even the LHC can't accelerate it's minute mass of protons to c and that uses a colossal amount of energy.

1. Re: It's my understanding.....@Chemist

"I suggest you read a little SR"

I know that's what the maths says. But why? In effect this says that mass increases as speed approaches light speed (or the effect is the same), and I don't understand why that is the case.

In the largely gravity free vacuum of space, what causes this?

1. Re: It's my understanding.....@Chemist

I don't think anyone can give you a 'simple' explanation for this. Many topics are rather inaccessible to analogy - the theory and the mathematics give certain predictions and measurements agree.

It's not the only theory to be 'difficult' - the predictions of quantum physics are equally difficult to rationalize.

1. But Why?

You might as well ask why energy increases with the square of velocity in classical mechanics?

1. Re: But Why?@JDX

"You might as well ask why energy increases with the square of velocity in classical mechanics?"

Well isn't that just e=mc^2 ?

Given that we're not getting very much further than "because that's what the theoretical maths predicts" on the question of light speed, maybe you're right, and the answer is intrinsic to why energy increases with the velocity squared. I accept it does, but why?

If my speed doubles, why doesn't my energy level merely double?

1. Re: But Why?@JDX

Given that we're not getting very much further than "because that's what the theoretical maths predicts" on the question of light speed,

I'm not sure what the antecedent of your "we" is here. If you mean "people commenting in this forum", then perhaps that's an accurate statement; but if you mean "human beings in general", you're hugely underestimating the vast array of experimental results confirming relativity, and the very nuanced understanding of it that researchers have.

maybe you're right, and the answer is intrinsic to why energy increases with the velocity squared.

No, the special status of c as the upper (asymptotic) limit on the speed of a mass doesn't derive from the relationship of velocity and kinetic energy in classical mechanics. I think you misunderstood JDX's point, which was that asking "why?" in some cases is rather difficult to explain. One problem is that the domain of the desired answer isn't clear. I can explain "why" E=1/2 mv^2 in classical mechanics in terms of calculus (ie, derive it mathematically from other observations about mechanics) - that's a formalist why. I can explain "why" in terms of experimental observations - that's an empiricist why. I can offer an explanation that appeals to the well-formedness of the universe (metaphysical) or the goodness of God (theological) or what have you. "Why?" by itself is an underdetermined problem.

I accept it does, but why?

Well, you could try starting with this: https://en.wikipedia.org/wiki/Lorentz_transformations#Visualizing_the_transformations_in_Minkowski_space. That visualizes what's happening between the two frames of reference (stationary observer and moving particle or whatever). If you understand those diagrams - and I admit they are not the sort of thing most people deal with on an everyday basis - then you'll see that there has to be a transformation to map the coordinates of one frame to the other frame.

Lorentz (with many refinements by Poincare, but he gave Lorentz credit, as he was wont to do) mucked about with Maxwell's equations, trying to understand the velocity of light and the symmetries of electromagnetism, and figured out the transformation in question. The key to it is that the speed of light is the same for all observers, which means that, as the Wikipedia article puts it, "the Lorentz transformation must preserve the spacetime interval between any two events in Minkowski space".

That there preservation of your spacetime intervals is what gives you yer c speed limit.

If my speed doubles, why doesn't my energy level merely double?

Because then mechanics would be inconsistent. Many of the basic equations of mechanics are just the derivatives and integrals of one another. Velocity is the derivative of position - it's how position is changing at any given moment - and the integral of acceleration, the overall result of whatever acceleration has been doing in a given interval. If kinetic energy were proportional to velocity (rather than to its square), and you derived energy from momentum (which is proportional to velocity) and then derived momentum back from energy, you'd have a different equation than the one you started with - and so two inconsistent equations for momentum. And so on.

In particular, if E was, say, 1/2 mv, then its derivative (holding m constant) would just be 1/2 m, and momentum wouldn't be affected by velocity. Well, that's a problem. The derivative of 1/2 mv^2, on the other hand, is mv, which is just what we want.

If you get an introductory physics text and spend some time deriving one linear-mechanical quality from the others, you'll find that the v^2 has to be what it is, for mechanics to be consistent.

2. Re: But Why?

"You might as well ask why energy increases with the square of velocity in classical mechanics?"

It doesn't - the classical equation for kinetic energy is 0.5mv^2

The equation for relativistic kinetic energy is :-

E=(mc2/sqrt(1-((v/c)2)))-mc2

1. Re: But Why?

Apologies - I didn't read the original post accurately - let's say classical kinetic energy is proportional to the velocity squared.

8. We've got a few years to go yet

Cubert J. Farnsworth: That's impossible. You can't go faster than the speed of light.

Professor Hubert Farnsworth: Of course not. That's why scientists increased the speed of light in 2208.

9. Actually

"It's one of the "difficult" bits of relativity: even if you and I are travelling in opposite directions at 55 percent of the speed of light, the sum is 100 percent, not 110 percent"

actually, .55c +.55c = .84c

1. Re: Actually

That's very interesting and a worthwhile comment to make, however, that Wikipedia reference just fused my brains so thanks very much.

10. Not really anything very new

The implications of special relativity are quite simple - lightspeed is a barrier to going faster than light as transition requires infinite energy. On top of that you might also consider that it can be viewed as a theory about simultaneous events and anything going faster than light maps onto a reversed time line. That is, to an observer, anything moving relative to them faster than light will appear to be moving in time. The end result is that transluminal travel creates time travel causality problems.

Bottom line tends to be that there aren't any rules saying you can't travel faster than light, just rules that say you can't get there. The natural 'speculation' is to imagine quantum tunnelling through the light speed barrier but since it is infinitely high this doesn't make sense either. The whole area has been done to death many years ago.

1. Re: Not really anything very new

Not necessarily. If we assume faster than light is possible (only getting there from our side of v= c requires infinite energy so is not possible to attain from our side of the light barrier) then you may have to accept that imaginary time exists.

That is, if you travel at velocity 2c then your mass would be restMass/i , or -i*restMass, whatever that means. If it means anything then it follows that velocity can take values on the entire complex plane. Special relativity equations for mass and energy simply have a pole at v = c. But that doesn't stop us side-stepping the pole and heading into complex velocities and then back onto the real line after meandering past the pole. Again, this assumes complex velocities means something. i.e. travelling through an extra space dimension.

For the last footnote, the sum is actually something like 84%, not 100%.

Oh Really?

Someone get me a calculator. And a slide rule.

Hey I didn't say he was wrong. I just wanted a more exact figure.

0.8445297504798464491362763915547

Anon in case I'm wrong ;)

12. bleh

"The surprising outcome: with just two assumptions"

I don't think much of the assumptions made. I can make two assumptions and give a whole different graph (although, I'll admit, I only play part-time with neutrinos as I design particle accelerators in my spare time) but this article smacks of 'having an interview and needing to get some use of it'

1. Re: bleh

"We made two assumptions. 1) Cheese makes great bicycles 2) FTL is possible.

We sent these assumptions through a grinder, and wow, FTL is possible!"

2. Re: bleh

And your comment smacks of sourpussing, and I need no assumptions for that at all.

13. I've seen things you people wouldn't believe.

[laughs] Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tannhäuser Gate. All those moments will be lost in time, like [coughs] tears in rain. Time to make some really cool quilts.

14. Light is.. just light?

photons travel at their natural speed without any extra input.. We can break the sound barrier... beating photons in a race shouldnt be that hard... be interesting to see what happens when you approach the FTL barrier.. does everything get blurry and then blackout?

Just remove the bosons and add energy?

15. This cosmic speed limit...

...sucks.

Who made it 2141.38M linguini/s anyway? Can't the noodly appendage count any higher?

I say put the Germans or Clarkson in charge and we'll have free speed in some parts, so we can visit the neighbours in a reasonable amount of time.

"Australian" and "Mathematician" fits like "American" and "Sensible" anyway. So there.

16. Relativity, causality, FTL: Choose two

There's also the small problem of causality: if FTL is consistent with relativity, relativity is still true, and FTL is possible, suddenly our concept of causality is thrown out of the window.

As far as I can understand, that does not change with this paper.

Do we really hope to live in an universe where retro-causality is true?

1. Re: Relativity, causality, FTL: Choose two

Bravo, sir, for being the first commentard to point out the what-should-be-obvious, and rather showing up said commentards (and reporter) above.

Unless there is a way to arrange FTL travel such that causality paradoxes are avoided, it cannot be possible.

These sorts of articles strike me as having got things backward, because it is a resolution to this issue that is required first before it's even worth bothering to think about how to go about doing it.

Having said that...

>>> Do we really hope to live...

A few commentards above talked wistfully about hope and dreams of a more positive sort. I'm down with that, but hard reality is a better guide. I'm afraid the same goes with the negative - if causality paradoxes are somehow sustainable, well then I suppose we're all fuct if we ever work out how to exploit the fact. The universe does not give a two penny shag what your little monkey brain has dreamed up as "hope".

1. Re: Relativity, causality, FTL: Choose two

It depends if time and speed really are linked as we currantly think. To our currant knowledge causality breaks if we acheve FTL, what happens if our currant knowledge is wrong?

So yes your right, but hopefully your also wrong. But you might be right and wrong at the same time...or yesterday.

1. Currant Knowledge

What the hell has dried fruit got to do with any of this?

2. Re: Relativity, causality, FTL: Choose two

If timeand speed are not really linked as we think, relativity is not true, and so my statement remains: causality and FTL remains, and relativity goes out of the window.

Said that, relativity have been verified at quite an impressive range of conditions, so to throw it out of the window is not a small task.

2. Re: Relativity, causality, FTL: Choose two

The part about hoping to live was directed to those that when you speak about FTL suddenly start jumping around all happy like puppies... if causality is not assured, our very existence become very precarious.

Said that, I agree with you that what it is, it is: when exploring nature belief have to remain out of the window.

3. Re: Relativity, causality, FTL: Choose two

if causality paradoxes are somehow sustainable, well then I suppose we're all fuct if we ever work out how to exploit the fact

Some hard-SF authors have played with this idea. I'm currently reading Charles Stross' Singularity Sky (among too many other books). One of his theses is that FTL travel is possible, but it's policed by a future civilization which uses its technology to maintain a monopoly on causality weapons. Anyone else tries to get clever with causality and they slap 'em hard - and they can do so before their opponents even develop a causality weapon, because they can change the past.

So we can go ahead and screw up causality in the hope that someone else already got there and will bail us out retroactively. Problem solved! Before it even became a problem, in fact.

Of course, the simplest fix is for the first civilization that develops causality weapons to prevent anyone else from ever inventing FTL tech.[1] So there's another reason why it won't happen. Sorry, FTL-travel fans.

[1] Because they can do this retroactively, they don't have to be the first first civilization to develop FTL. The first civilization to develop FTL and get the idea to stop everyone else will retroactively prevent any earlier civilizations from developing FTL, and thereby become the first to develop it. Simples.

4. Re: Relativity, causality, FTL: Choose two

I sure hope you don't think anyone with dreams is a "tard" (how am I supposed to take that "commen<i>tard</i>" remark, anyway?<i>!</i>). Remember, with that kind of attitude, we'd still be in caves.

But yes, one does need "hard reality" to tell one <i>which dreams can be made to come true and which ones can't<i>. But that doesn't mean one shouldn't have dreams. A knowledge of "hard reality" tells you where you can go, can't go, how hard it is to get there, and, of course, <i>how</i> to get there if you can get there. But the <i>desire</i> to go and the <i>direction</i> in which to go requires, at some level, dreams. The two work together.

17. ....tnemirepxe thguoht a did tsuj I

:) thgil fo deeps eht ekorb dna....

1. Re: ....tnemirepxe thguoht a did tsuj I

Smiley is the wrong way around

1. Re: ....tnemirepxe thguoht a did tsuj I

@P_0

No, I think he's got the smiley right ( :

18. But what if one of the observers were short sighted?

19. What I don't get is the obsession with going faster than light in the first place.

Yes, it would be better if we could get to very far away star systems in months or even a lifetime but if you are talking about the expansion of the species then why does that even matter? Even if it takes centuries to "system hop" there will be pioneers willing to be part of that either through stasis pods, generational ships or whatever. Yes it'd be a 1 way trip but so was emigrating to another country thousands of years ago.

1. Why?

Because!

If there's a limit, there's been a talking ape that tried to figure out how to get past it. If there's a horizon, there's always someone who's going to look what's beyond it. If "everybody knows" [something], there's someone figuring out how everybody has been wrong all along.

As soon as humanity loses this trait, we're truly doomed.

20. If we are concentrating on travelling faster than light, surely we can come up with some inventive ways to massively slow down the light? So much so that we can perform an experiment where someone gets to the destination quicker than light. Thus, claiming the prize and the adoration of all

Alright, they subjects would be travelling through different mediums, but this is all about making spurious claims, not about fair tests.

x

1. so your plan is to slow down the universe, and then simply walk to alpha centarui? Basicaly a cheats version of FTL? Its inventive, but i suspect horribly flawed.

2. Slowing down light is trivial

The current record, if I recall correctly, is something like walking pace. (I'm sure it's been reported here if you care to look.) C on the other hand is a fundamental physical constant. Unless you happen to be a member of the Q continuum you don't get to change it. It's simply a part of how the world works.

Now that doesn't mean there might not be workarounds but those workarounds need to be compatible with relativity in much the way relativity is compatible with Newtonian physics.

3. I know exactly how to slow down light. All you need is a flask of water.

Unless you are talking about speed of light in a vacuum. Which is really the maximum speed information can be sent. i.e. the maximum possible velocity for sending information. Ever. Even quantum entanglement experiments don't truly break this limit (that is, entangled particles separated by a great distance acting as an entangled pair). Since the observers of either particle would not be able to get information about the other particle faster than c.

21. ı ɟəəl sıɔʞ¡

22. Betteridge's Law strikes again

...which states that any question in a headline can be answered "no".

I think I first read about this in A Brief History of Time: physics doesn't ban FTL particles, but c is a barrier which cannot be crossed (so how do FTL particles get created in the first place?).

23. This post has been deleted by its author

24. The light speed limit only applies to things moving - e.g. quantum entanglement effects are, as far as we know at the moment, instantaneous. Similarly the (very) early cosmos is thought to have expanded faster than its local speed of light.

Or, consider looking at a spoon in a glass of water; it appears bent due to the effect of refraction at the air/water boundary, which is an effect of the different speeds at which light travels through air and water. If you now move the spoon around, the "bend" changes in a predictable way which can be calculated by assuming the light travel time is minimised (by trading off speed vs distance in air vs water). Which begs the question of how do the photons involved know which combination of paths in air and water will produce this minimum time - perhaps something is working it out for them in advance, implying a faster than light effect. Or not.

1. This post has been deleted by its author

2. I've not explained this brilliantly. I could have another go if needed...

Shortest path provides a very handy way of calculating for us, but it doesn't mean that the universe does some calculating ahead of time.

Here's an analogy; when you drop something, it falls in such a way as to preserve various truths/values about its energy (and there is a way of calculating this that provides some very elegant maths). How does it know in advance which way to move to do this? Does it calculate all possible options? However, apply Newtonian mechanics to the exact same situation, and it falls in the direction that weight (i.e. the force due to gravity) applies. This explanation does not "require" any pre-calculation about which way to fall to do the same thing to its energy - that is a by-product of obeying the Newtonian mechanics.

Which is "correct"? Both methods give the same answer, verified by experiment. They are two different mathematical ways of describing the same phenomenon and the fact that one of them involves "knowing" which path is the path that meets requirements on its energy doesn't mean that something somewhere is calculating all the options.

1. Re: I've not explained this brilliantly. I could have another go if needed...

Here's an analogy; when you drop something, it falls in such a way as to preserve various truths/values about its energy (and there is a way of calculating this that provides some very elegant maths). How does it know in advance which way to move to do this? Does it calculate all possible options? However, apply Newtonian mechanics to the exact same situation, and it falls in the direction that weight (i.e. the force due to gravity) applies. This explanation does not "require" any pre-calculation about which way to fall to do the same thing to its energy - that is a by-product of obeying the Newtonian mechanics.

Agreed. To put it another way: if the dropped object didn't follow the path of least effort, it would be moving away from a lower potential energy state. That means you could in principle take the difference between the state it did move to, and the actual lowest state, and extract energy from it for free. You'd be violating thermodynamics (and the authorities take a dim view of that), you could build a perpetual motion machine, you'd be inflating the universe, etc.

3. The VERY short answer... photons don't need to know, they just try it all

1) Check out Feynman's books on QED (there is one for the lay public and one called "Feynman Path Integrals" or something). The idea:

You "just" need to add the complex amplitudes (at the target) of EVERY POSSIBLE PATH that a photon might take from source to the target. Square the value, which gives you a classical probability density function. A photon will be detected according to this PDF.

Everything (shortest path through spacetime, diffraction, refraction, Heisenberg uncertainty, interference, the works) can be explained by this simple principle - use EVERY POSSIBLE PATH (also the fractal ones - especially the fractal ones, though Feynman didn't know about that adjective, I think - and even the ones going faster-than-light, to the edge of the universe and back) AND SUM OVER THEM. For every photon. There are exponentially more paths in case you have more particles. Tremendous computational capability in this universe, wouldn't you think (but sadly NP-hard problems stay unsolvable even so)

2) In classical mechanics, you have the "Lagrangian formalism" which gives you the path an object takes through (flat) spacetime by requiring that INTEGRATION OVER TIME OF THE DIFFERENCE BETWEEN KINETIC ENERGY AND POTENTIAL ENERGY SHALL YIELD AN EXTREMUM. Simple as that. And it works bombers. Time disappears and the classical trajectories are simple solutions of a minimization procedure. Great stuff! (not so great that it would allow you do NP-hard problems efficiently though)

What does it all mean? Nobody knows.

25. I don't get it ...

What is the difference between travelling just under the speed of light and just over it?

My point being, if we could devise some "ship" that would take a human to a speed just under the speed of light, why would we not be able to devise a "ship" that travels just a bit faster than that?

as suggested above .... if I can build a car that travels at 40mph why can't I create a car that travels at 60mph if light travels at 50mph ?

How does light somehow prevent us going any further?

Surely it just prevents us "perceiving" going any faster than actually moving any faster?

Or is that just too simplistic a view?

1. Re: I don't get it ...

"can't I create a car that travels at 60mph if light travels at 50mph "

The normal, simple model for this is as the speed of light is approached the mass of the vehicle actual increases in a non-linear manner so that more and more energy is required to accelerate it. The mass becoming infinite at c unless the original rest mass was zero.

This might sound like madness but in particle accelerators that is precisely what is seen, furthermore time itself alters so that short-lived particles have a vastly increased lifetime. This all predicted by SR.

Reality is pretty weird

1. Re: I don't get it ...

Interesting, but doesn't this assume a "traditional" approach to propulsion?

If for example, we found a way to propel an object to say 50mph with only the force required (using the current "traditional" approach) to get that object to 40mph then I guess we break the theory of relativity or something.

I'm also guessing that (with my limited understanding of things here) it is assumed that light is a constant for some special reason?

My thought on this is that a lightbulb "radiates" light, thus using energy to "propel" something we can see?

I guess this comes back to the debate over light being particle / wave, but that said is a light not capable of producing enough power to get something to the speed of light?

And ...

If a lightbulb can do this why can't a nuclear reactor?

Probably a dumb question, and likely oversimplifying this ... but my point is, what we don't yet understand is what is needed to get something to move anywhere near the speed of light, when we figure that out we can determine if going beyond that is actually possible.

My thoughts being ...

If we can't go beyond the speed of light, we may never send a person outside our solar system.

Kinda puts a major downer on space travel and colonising other planets don't it?

I guess the good thing about theory is ... its only theory, so any limits can probably be replaced with a workable solution.

But didn't you see transformers 3 ... apparently Einstein is wrong, ask optimus ;)

1. Re: I don't get it ...

"lightbulb "radiates" light, thus using energy to "propel" something we can see?"

AFAWK the proton mass is zero - so it can travel at c, indeed in a vacuum it HAS to travel at c. VERY light mass particles like neutrinos can get very close to c which explains why there was so much confusion over the CERN/Grand Saaso experiment recently.

SR is a very well tested theory and physical measurements at close to light speeds on particles in accelerators match the theory.

I don't know why people EXPECT the universe to be set up to allow us to explore the stars - don't get me wrong I'd love it -but it doesn't mean it will happen

2. Re: I don't get it ...

"Or is that just too simplistic a view?"

Yup. Even Paris knows it.

And I can't believe no-one's posted this yet: Speed of light in a bottle http://www.youtube.com/watch?v=Y_9vd4HWlVA

3. Re: I don't get it ...

Things would get pretty darn weird, since we use light for sensing our surroundings, but the point is the relation between mass and energy. You can keep adding energy to accelerate a unit of mass (i.e. making your car more powerful). something like

speed = mass * Energy * (some constant).

[I think the real equation, at least for GCSE is e = 0.5*m*v^2 => v = square root of (2e/m), this disregards all losses, like transmission losses and air resistance]

You know that photons have no mass and you also know that photons travel at a certain speed. So you try to work out how much energy it would take to obtain the speed of a photon and you do some algebra and you end up with

(speed of photon) = (mass of photon) * (energy of a photon) [we don't need to care about the constant]

=> (energy of a photon) = (speed of a photon) / (mass of a photon).

You plug in (mass of a photon) = 0 and you realise you need a better equation (and hopefully someone who understands partial differentiation and Maxwell's equations can help you further).

4. Re: I don't get it ...

There are two issues that are counter-intuitive. Firstly, how we all add velocities in a normal common-sense way is wrong. It is nearly enough right if you are dealing with slow things like cars or bricks but it is in fact incorrect, and the proper way to add or subtract relative speeds can be derived in a straightforward way, see Lorentz instead of Galilean transformation.

Second, the maximum speed limit (that the first point relies on as an assumption) actually falls out of the nature of spacetime - it is a fundamental parameter of our universe, in the same way as the strength of gravity or the value of the charge on an electron is.

So, sadly, you can't just strap more rockets on and keep getting faster til you break the limit.

26. Slow

The speed of light does seem rather slow, cosmically speaking. I mean, compared with the distances etc such a slow thing as light seems, well, out of place somehow.

Perhaps soon we will discover a new "light" that runs at a faster speed, this will open up all sorts of comms and travel opprtunities, and have the happy by-product of driving the maths guys potless.

It is the duty of science to keep an open mind, you can't just say that somenting can not exist or be, you have to seek and then observe.

Ok then who's up for it, etc

1. Re: Slow

food for thought ...

If i'm travelling near the speed of light and fire a bullet from a gun i'm holding will the bullet slowly leave my gun because it can't possibly travel faster than the speed of light :)

The speed of light (in my opinion) is the speed at which perceptable light travels based on our point of reference.

If stationary the speed of light is therefore c when moving light is potentially c + my speed is it not?.

another key point ...

because i'm nearly travelling at the speed of light whilst holding my gun would I be incapable of running around in my ficticious spaceship?

1. Re: Slow

AFAIK and this is where it gets weirder.

If you fire a gun, in your local frame of reference ( the ship ) the bullet will exit at it's normal muzzle velocity as far as you are concerned.

HOWEVER an stationary observer relative to you will still only see a slightly increased speed of bullet. This is the same kind of thing as 2 observers approaching each other at 0.55c only being seen to close at ~0.84c relative to a 'stationary' observer.

1. Re: Slow

No, or at least your wording is confusing. To each ship the other appears to be receding at .84c because in each case I have to add the two velocities together and I have to account for relativity when I do so. However, to a stationary observer standing right in the middle the two are separating at a combined rate 1.1c. Note that it is the space between them that is exceeding the speed of light and not the objects themselves. The same is true for a warp drive that compresses space in front of the ship and expands it behind. From the perspective of the ship it never exceeds the speed of light even though the space which it occupies does.

2. Re: Slow

Congratulations. (I'm not been sarcastic.) You've actually clearly stated the major commonsense assumptions that relativity violates.

If i'm travelling near the speed of light and fire a bullet from a gun i'm holding will the bullet slowly leave my gun because it can't possibly travel faster than the speed of light :)

No, because velocities in relativity don't add in that way as described above.

If stationary the speed of light is therefore c when moving light is potentially c + my speed is it not?.

No because a fundamental premise of relativity is that c is the same for every observer no matter how they are moving. This isn't just an assumption but an experimental result (look up the Michelson Morley experiment) that relativity explained. Also there is no such thing as 'stationary'. That's not strictly a result of relativity, but relativity's description of how relative velocity work pretty much put paid to any hope that the universe has some preferred velocity against which all others are measured.

because i'm nearly travelling at the speed of light whilst holding my gun would I be incapable of running around in my ficticious spaceship?

It follows from the last point that you're not really "travelling at the speed of light ". You maybe with respect to say the Earth, but if so it's equally true that the Earth is " nearly travelling at the speed of light " with respect to you. What matters is that if "nearly travelling at the speed of light " is say .999 c and your gun fires a bullet at say 0.002 c the velocity of the bullet with respect to the Earth is still going to be less than c. Counterintuitive, yes but the fact is space and time simply don't work in the way our commonsense tells us they do.

1. Re: Slow

Eh that's hilarious ...

So (by that logic) the speed of light is effectively not constant if no matter how fast something moves it's still in fact moving slowing than this fictitious speed (the bullet)?

"relatively speaking" it makes sense though, something moving very fast then something moving faster than it is still seen to be moving very fast thus difficult to make an accurate measurement of its actual speed.

so for arguments sake lets assume light moves at 1 million metres per second.

Does that mean its impossible to move at 1.1 million metres per second?

All that would mean is that something could happen before it would be observable surely?

1. Re: Slow

Why assume light moves at 1 million m/s - it's KNOWN to move at ~3E8 m/s in a vacuum=c

If you or anyone else set up to measure it, no matter how you or they are moving it will still be measured at c.

You can't just travel at c+ or even c as the energy necessary to accelerate you becomes infinite. I've written the equation for relativistic kinetic energy in a post on this topic

If you are really interested the net is full of information about special and general relativity.

.

2. Re: Slow

> The speed of light does seem rather slow, cosmically speaking.

It has exactly the value it needs: 1

RobotRollCall wrote an excellent piece on the light speed limit over on reddit. It's well worth reading and explains why we can't exceed the speed of light by just going faster and faster, without having to resort to clumsy "it would require infinite energy so it's impossible" type explanations.

this is a brilliant answer ROFL

... I love the response to his answer too :)

28. Light or Gravity?

I've always wondered what would happen if we were to learn that c was the speed of gravity and light was limited to that for some reason.

1. Re: Light or Gravity?

isn't gravity proportional to the mass of an object ...

Therefore, does light move faster when closer to a bigger object, so if I want to appear to lose weight could I look thinner by slowing the light around me?

1. Re: Light or Gravity?

"does light move faster when closer to a bigger object"

No. Worst than that you are now edging dangerously close to General Relativity

2. Re: Light or Gravity?

"Therefore, does light move faster when closer to a bigger object, so if I want to appear to lose weight could I look thinner by slowing the light around me?"

Isn't it time slows down closer to a bigger mass, so wouldn't c be consider slower relatively to an observer further away? Thus you could go faster than that c "over there" because it's slower than your c? ;) Or something obsurdly Douglas Adamesque.

Beats me. Time for breakfast at Milliways I think.

1. Re: Light or Gravity?

"time slows down closer to a bigger mass"

Mass alters spacetime and seriously affects time near large masses, but c is c

2. Re: Light or Gravity?

Downvoted because breakfast is at the Big Bang Burger Bar.

(Mine's a Pan Galactic Gargle Blaster.)

We have already learned this. c is the speed of gravity.

29. FTL - easy-peasy...

Travelling faster than c (as in "reaching a star x light years away in less than x years") is perfectly possible - it's getting back in time for tea that's the problem...

1. Re: FTL - easy-peasy...

"is perfectly possible "

Well potentially possible as you need to go moderately close to c, say 0.95c, but where is the energy to get there coming from ? An (unrealistically ) modest 1000 tonnes ship would need 2E23 J to reach 0.95c - if the propulsion 'fuel' had to be carried on board that would add to the initial mass.

2E23 J is a LOT of energy. It's roughly 400 times the annual energy production of Earth.

1. Re: FTL - easy-peasy...

I don't think it quite works like that (but I could be wrong). Apart from anything else, remember that your propulsion mass is increasing too...

Thought experiment - can the people on the ship measure that they have more mass? If not, how would they explain the sudden need for shed-loads of energy?

30. there is already something faster than light

its called energy. energy doesn't know time, distance or any boundaries. A thought can "travel" a million miles in just one eyeblink. or though can also "travel" in time for instance million years back or million years into the future also in less than a second. it is the limited mind that wants to find proof in physical world to back it up with. but I dont think there is a need for that at all.

1. This post has been deleted by its author

2. Re: there is already something faster than light

"but I dont think there is a need for that at all."

Judging by the contents of your post I imagine that you wouldn't !

3. Re: there is already something faster than light

I down-voted you and el reg said it was sorry I didn't like your post. This is not true. I loved your post. Still chuckling...

31. Four Dimensions Not Three

The explanation that it would take infinite energy to accelerate mass to light speed is a *consequence* of Einstein speed limit, not an explanation why FTL is not possible. Einstein relativity describes a universe in which time is just as much a spatial dimension as our other three dimensions. The important element of the theory is that if an object was standing still in 3d space, then it is moving across the time dimension at the speed of light. The speed of light basically gets pegged to an object's potential energy. This was based purely on the observation that even if you accelerate towards or away from a light beam, you still detect it traveling at the same speed. In order to move through the other threee dimensional then, you have to slow down along the time dimension. All other aspects of Einstein's theory come from this fundamental merging of space and time and the observation that the speed of observed light remains constant regardless of your own speed.

32. c is the speed of light (i.e. of photons) through a vacuum, i.e. space.

Photons have been slowed through other mediums, e.g. sodium and the vacuum of space potentially is not an 'easy' medium to travel through, e.g. potential of dark matter/energy etc. so why couldn't it be theorised that a photon could potentially travel faster through a 'cleaner' vacuum?

A photon is just another particle - potnetially others particles out there that travel faster.

Time is not linked to the speed of a photon, only what we can observe and currently measure.

The maths currently gives the limits - the maths is based on current experiments, thinking and observed results, all of which could be wrong as they have been plenty of times in our past...

1. but c is not the speed of light - it is the speed that any particle with zero rest-mass MUST travel at. Actually, and iirc, it is more complicated than that. In a sense, everything travels at speed c all the time - it's just that massless particles travel at c in 3d space as well as 4d space-time.

In other words, to travel faster than c requires you to behave differently from every other particle in the universe.

33. Imagine what you will know tomorrow

Couple of centuries ago the greatest minds of this planet were absolutely sure that human beings could not survive traveling at speeds of 30mph

34. wishing doesn't make it so

well then, what a bunch of fluff.

sorry guys, it's not happennin'.

and furthermore, humans are limited - what is known as a finite being.

It is a good idea to remember that you are not God.

35. If the universe is expanding faster than the speed of light, then yes it is possible to travel faster than the speed of light. Humans will always have limits until they are broken. It would require a different fuel source since energy levels are different depending on the fuel source and a different type of engine. If their are aliens, which history suggests, then how could they successfully travel to our planet if they are limited to the speed of light. Sure worm holes is possible. Maybe worm holes + faster than the speed of light. One day, not in my life time, if humans will still exist, I believe we will surpass the speed of light.

36. we have yet to understand light

There has been numerous researches on going faster than the speed of light. This is a dangerous experiment, considering our lack of research on light itself. To my knowledge, there has yet to be proven papers done on connecting the visible spectrum to the non-visible spectrum. My own hypothesis would be to take a strip of paper. And starting at the top, start writing red, then below red; orange, yellow, green, blue, violet, ultra-violet, ultra-blue, ultra-green, infra-yellow, infra-orange, and finally infra-red. now bend the paper into a circle so that infra-red, that is at the bottom of the strip, touches red. A circle that connects the known lights together.

But, there has been very little research done on the invisible spectrum of light. Though this appears two dimensional, i believe there to be a third dimension that turns this into an orb. For every action, there is an opposite but equal reaction. For every red, there will be an infrared and so on. And, just like matter and anti-matter, there is an anti-light that turns this illustration into an orb. Our ocular system just catches glimpses of the outer edge of light. We have the technology to build equipment to better understand light, but it has become a lost science after the discovery of infrared and ultraviolet.

All molecules, atoms, etc.. take on an orb shape, but light seems to be treated differently. Also, our ignorance, or lack of understanding of light, has put so much limitations on our search for life on other planets. We define life as things that are carbon formed and fall within our light spectrum.

Until we start fully understanding light, it is dangerous to be experimenting with the speed of it, We should have learned from the speed of sound, and the ultrasonic boom that goes with it, after breaking the sound barrier. There has to be consequences, like the sonic boom, for breaking the speed of light.

I hope, for everyone's safety, that the speed of light will not be broken until we better understand light itself.

1. Re: we have yet to understand light

http://en.wikipedia.org/wiki/Electromagnetic_spectrum

2. Re: we have yet to understand light

Why are so many cranks emerging in this thread, seemingly from before the french revolution considering their state of knowledge of contemporary physics and Lorentz boost operators?

Has someone opened a Portal by testing FTL devices again??

IGOR!!!!

37. This post has been deleted by its author

1. >>> the Earth is only some 10,000 years old or less

Well it is - from the right frame of reference!

38. So if the speed of light is the maximum speed we can occomplish, why cant we reach the speed that allows us to break free from a blck hole that rotates faster than the speed of light, there for capturing it as we are all aware of. The speed of light can be surpassed. Just like lifting a 50 ton rock.

For a tech-site, I'm amazed at the fundamental ignorance shown by many posters of the basics of relativity.

How can people spend what appears to be quite a lot of time dreaming up nonsense when a little reading would at least give a basic understanding of the principles (which have been proved time and time again in the lab)?

1. Re: Am I On Youtube?

Labs are boring some people have a life.

Who cares what "the theory" dictates, everyone has an opinion that "speculates" one way or another.

Either way, speculation is all we have at this point until finite proof is found that it either is or isn't possible.

1. Re: Am I On Youtube?

"Who cares what "the theory" dictates,......"

I think you are reinforcing Tom Melly's excellent point with a post like this

2. Re: Am I On Youtube?

... and apparently they're spending their life talking (and thinking) bollox.

... and that's ignoring the fact that 'boring' in this case is referring to experimental evidence that time and space change their relative dimensions in order to maintain a constant value for c.

3. Re: Am I On Youtube?

"everyone has an opinion that "speculates" one way or another."

So why waste your time posting here - your speculation is obviously as good as anyone's .

I can understand it if you have no interest in this but simply to spout uninformed guff and then claim it's all too boring and anyway 'nobody knows' is juvenile in the extreme. It's clear from your posts that you've never tried to educate yourself about this other than by asking naive questions here and then complaining when you didn't understand the answers

1. Re: Am I On Youtube?

>>> "everyone has an opinion that "speculates" one way or another."

Ummn no, some people are interested and would like to further their own knowledge/education, even if they're not interested in becoming theoretical physicists.

The OP has a point that for the Reg there is evidence of some alarming evidence of science illiteracy amongst the commenters in this thread.

4. Re: Am I On Youtube?

Labs are boring some people have a life.

An unexamined one, presumably.

until finite proof is found that it either is or isn't possible

I don't think you understand what "proof" means. Or "finite". Or, probably, "possible". You seem pretty clear about "either", but it's redundant.

5. Oh the huge manatee!

> Labs are boring some people have a life.

Translation: Too dumb to learn. Will watch Lindsay's arse instead.

> Either way, speculation is all we have at this point

40. Relativity....Whatever...

I'm off to ask the Zeta Reticullans (eben) what they think....

1. Re: Relativity....Whatever...

Good for you. I shall expect your results above (before) this one. Don't cheat by looking at your own message.

41. Wot I Fink

Without a shadow of doubt LightSpeed are the absolute limit with their continued attempts to game the system and demand everyone else pays for the privilege.

Oh, wait. Is that not what we're talking about?

42. There already is something that travels faster then the speed of light otherwise Quantum Entanglement would not be possible.

Interesting eBook about how these tie in with consciousness as well if anyone is interested. www.TheRealityCode.com.

For the world we experience via our physical senses, the speed of light is a absolute limit, but for the reality that is the Quantum, atomic, and possibly even the molecular foundation of our Universe, speed is instantaneous.

43. "Light speed" is not one word.

When writing an article, do try to get the spelling of the item your article discusses correct.

It's "light speed", not "lightspeed".

44. GET OVER IT!

Jesus - people still whingeing about not being able to travel faster than light? In a couple of decades we're more likely to be back riding donkeys than travelling to Alpha Centauri.

45. V = D % T ; and there are no independent measures of D & T

The "speed" of light is not a speed .

Because there is no measure of time or distance independent of it . Thus all measures are ratios , hence Lorentz geometry .

It's simpler to just make c = 1 , then all other measurements are seen as simply ratios .

46. if you travel faster than the speed of light you travel back in time,

so if a bullet left the gun at 13:02 and went back in time then it get to the target at 13:00.

to a observer it appers that it left the target at 13:00 and went in to the gun at 13:02.

it would appear to be traveling slowly into the gun (backward) this might be happening all around use now..

47. what's the point?

What's the point in linking to the Royal Society's article? I mean, the subscription is a bl**p'n 1,6 k€ and the article itself is 26€, only for 1 month, ah the misery!

Hardly convenient. And people wonder about the mounting ignorance of the populace... a peek at Paris usually come for free

48. Which infinity?

Is that the infinity(0) meters per second where infinity is the number of integers on the number line, or is the infinitely faster infinity(1) meters per second where this infinity is the number of points on a line?

1. Re: Which infinity?

Your gathering of infinities serves very little purpose. There can be only One.

This topic is closed for new posts.