Creates more problems than it solves?
Not just Einstein, but Maxwell and others.
I'm not convinced by the proposed "test" either.
Einstein was incorrect about the speed of light being a fixed constant in our universe, a new theory suggests. A team of physicists are backing an idea that the speed of light is not constant and have made a prediction that can be tested. The speed of light is exactly 299,792,458 metres per second, and is a value that is …
I thought the speed of light was a constant by definition.
Only as part of a hypothesis.
Newton did impressively well, Einstein took it further...but the probability that Einstein had it all figured it is....well...vanishingly small. We're just waiting for the next step.
I can solve problems.
Slow it down, speed it up, slow it down, speed it up, slow it.... does light friction exist? This tech. ("light") would work great as a scroll saw in my wood shop. At the gym, could I just increase the speed of my personal light to make it look like I'm doing a hard workout or at least slow the light of everyone else? Also, it would be nice to slow the light of internet ads, tweets and likes to 0mph if possible. How about markup? <light speed="0">You'll never see this</light>
The future looks bright for this "light" tech., I keep an eye out for solutions.
The speed of light is a constant from a given frame of reference. Thus in order for someone traveling near c to see the speed of light as a constant, time must slow down for them relative to an observer in a different frame of reference.
You're always traveling at the speed of light through 4D spacetime, so the faster your travel through 3D spacetime the slower your travel forward in the time dimension. Perhaps inflation is related to the speed of light in a similar manner.
Though if inflation causes the speed of light to be faster as theorized here, that 5th "inflation dimension" must be an imaginary number to work within the x^2 + y^2 + z^2 + t^2 = c^2 framework.
"the probability that Einstein had it all figured it is....well...vanishingly small. We're just waiting for the next step."
The probability that he had it all figured out is precisely zero. Many more advances in cosmology and quantum physics have been made since his days. But of course, many widely studied theories are still untested and therefore not accepted a\s fact. The idea of a different speed of light at the birth of the universe as an alternative to the theory of rapid inflation to explain what we observe in the cosmic microwave background radiation is an interesting one. If it could be proved or disproved by the proposed experiment then that would be a great step in the progress of physics. But it wouldn't invalidate general relativity, my guess is that it would mean that the cosmological constant may not have been constant after all. I for one hope that we'll see an answer to this soon(ish).
No, see for example: "How the Universal Gravitational Constant Varies", http://www.sheldrake.org/about-rupert-sheldrake/blog/how-the-universal-gravitational-constant-varies
Likewise, physical laws are often violated, eg. "NASA's Physics-Defying EM Drive Passes Peer Review", http://www.forbes.com/sites/briankoberlein/2016/11/19/nasas-physics-defying-em-drive-passes-peer-review/#1034b01076e2
Unless, of course, nothing in the universe is constant which leads to an infinitely variable universe which leads to the concept of an infinite universe which leads to the concept that there is no such thing as time - each instant of time is a one-shot configuration of the universe. So to travle in time one would have to reconfigure the entire universe to a previous configuration to travel back in time or reconfigure the entire universe to configuration that has not yet occurred to travel forward in time. That would get a bit difficult with an infinite universe, not to mention an infinitely variable universe.
“Why is geometry often described as 'cold' and 'dry?' One reason lies in its inability to describe the shape of a cloud, a mountain, a coastline, or a tree. Clouds are not spheres, mountains are not cones, coastlines are not circles, and bark is not smooth, nor does lightning travel in a straight line... [b] [u]Nature exhibits not simply a higher degree but an altogether different level of complexity[/u] [/b].” – Benoit Mandelbrot
What Mandelbrot has introduced is the concept of fractional dimensions. And fractions, being infinite, leads to the concept of infinite _dimensions_ on both larger and smaller scales.
> leads to the concept of infinite _dimensions_
Erm, no. That's a pretty fundamental misunderstanding of what fractional dimensions are.
To take the example you mentioned, of coastlines not being circles, the length we measure depends on the length of the ruler we pick to measure it. The fractal part is due to self-similarity at various scales and the overall "crinkiliness" of the thing being measured.
The thing is/things are:
* physical law determines that things have to bottom-out at the Planck scale, so any weirdnesses observed with your set of rulers is merely an epiphenomenon when compared with c/Planck-based metrics
* Mandelbrot's "nature" is not the same "nature" as in the "nature of reality" (whether it be relativistic, string-theoretic or multiversal or whatever); Mandelbrot's "nature" is stochastic and has underlying power laws
* using relativistic rulers is by definition the "wrong thing" when dealing with the fundamental nature of things; it's like measuring how "plaid" the universe is
* something like the fractal/Hausdorff dimension is a mathematical abstraction, not a real "dimension" (again, see power laws)
Besides, just because there are fractions doesn't mean that there have to be an infinite number of numerators and denominators (and associated explanations for them as separate things) in the universe. Unless you want to try to argue that, your argument falls apart.
I thought Trump had shown that taxes aren't either.While taxes are always there, they're never constant. During the election campaign, taxes are going to decrease. After the campaign is over, they increase. I believe some call it Pompous Git's Law ;-)
"Unless, of course, nothing in the universe is constant which leads to an infinitely variable universe which leads to the concept of an infinite universe which leads to the concept that there is no such thing as time"
That sounds infinitely improbable. Would you like a nice hot cup of tea?
the concept that there is no such thing as time
The End of Time (book)Julian Barbour, a British physicist with research interests in quantum gravity and the history of science advances timeless physics: the controversial view that time, as we perceive it, does not exist as anything other than an illusion. The philosopher J. M. E. McTaggart reached a similar conclusion earlier in the 20th C.
THX1138v2= Welcome to the Buddhist Religion..
The Universe has Always Been Here.. and probably goes on Forever..
With actual Infinity, Time is not relevant, any possible numeric system is actually Zero..
and so are we.. Do the best you can and try to do no harm..
IMHO= Becoming Aware is a wonderful experience..
All of our maths and sciences attempt to help achieve.. Nirvana.. RS.
"I thought the speed of light was a constant by definition. If you allow the speed of light to vary, then another measurement would need to be defined as constant."
The meter would need to be defined as a constant. The second is defined separately, the speed of light is defined as a fixed number of meters per secon, and the length of the meter is derived from that.
"The meter would need to be defined as a constant. The second is defined separately, the speed of light is defined as a fixed number of meters per secon, and the length of the meter is derived from that."
Except that defining the meter using the speed of light is a later modification to the definition. When the meter was invented and defined, the speed of light was not known.
When the meter was invented and defined, the speed of light was not known.The metre was invented on 17 March 1791. Ole Roemer estimated the speed of light at 200,000 km/s in 1675 and James Bradley gave the number 301,000 km/s in 1728.
Today of course Merkins know that it's 299792.4574 ± 0.0011 km/sec and the British know that it's 299792.4590 ± 0.0008 km/sec.
The metre was invented on 17 March 1791. Ole Roemer estimated the speed of light at 200,000 km/s in 1675 and James Bradley gave the number 301,000 km/s in 1728.
So the kilometre was used for measurements 84 years before the metre was invented? This relativity business truly is weird.
Yes, estimated. But in km/s? That was clever :-)Hopefully the smiley means you are just being a smart-arse :-)
Roemer never made the estimate in Earth-based measure; the conversion to km/s is so the modern reader can comprehend and compare. Huygens' estimate for example was a value of 110,000,000 toises per second, an amount incomprehensible to most people today (possibly when it was made, too). At El Reg it really should be percentage of maximum velocity of sheep in a vacuum, but I couldn't be arsed to work it out.
speed of light in a vacuum is assumed to be a constant. however, our velocity through time would have to be NOT decelerating for that to work... bremstraelung from tachions? interesting thought experiment.
Anyway, light speed in a vacuum is the absolute maximum speed something can go relative to something else. hence relativity.
light can, and does, attempt to go faster than it's supposed to through a medium and creates cerenkov radiation [did I spell that properly] aka "that blue glow" you see in photos of nuclear reactors operating in open pools of water. Those are various particles being forced to move slower because they hit water [and its speed of light is just a bit slower than the particle].
if our velocity through time is NOT a constant, i.e. is slowing down [or maybe speeding up] then light over time wouldn't be going "the same speed" any more. I wonder if THAT is what they're basing their theory on? yeah ok 'velocity' is time-based, so "changing velocity through time" simply means (by my definition) that the time axis isn't change at the same 'rate'. 1 second may not be 1 second a zillion years ago, in other words. If time flowed differently back then, the speed of light would ALSO be different [being based in time]. It would also mess up relativity calculations like E=mc^2 and so mass and/or energy is no longer a constant. damn them!
now I'll want to know where the mass and/or energy WENT to (or CAME from) when it changed over a zillion years' time.
now I'll want to know where the mass and/or energy WENT to (or CAME from) when it changed over a zillion years' time.I think you spotted the fatal flaw. Although it's "merely" an assumption that mass/energy is conserved, if it's not then there's a whole HEAP of physics out the window. Holy shit, Bob. I seem to have CAUGHT whatever it is YOU'VE got... ;-)
Relativity and classical electromagnetism (JCM got tantalizingly close to discovering special relativity if he hadn't died so young) only assume speed of light is constant for any observer in any frame of reference.
Admittedly it raises problems if it varies day-day but there is no problem with it being different in the early universe.
@Mage - It creates more problems for theoretical physics. However, all theories are our best navel gazing explanation for what we see. They are not necessarily very accurate or even true and when more observations and analysis is done their areas of wrongness and limitations will become more obvious. The fact they are testable means we have an idea of the area of validity.
"Not just Einstein, but Maxwell and others."
I didn't understand half the letter. But it's argument was that gravity and "light" (massless particles) dodn't propagate at the same speed. That's undoubtedly weird, but not necessarily fatal.
And while the author argued it was light that was faster, I saw nothing to say it couldn't be gravity that was slower (it's all relative...). Slower gravity is plausible if gravitons self interact -- they would naturally find the earlier universe stickier than the present day one.
So I read this as yet more evidence we don't understand gravity. Which, yes, means more problems for Einstein (cf dark matters vs MOND). But Maxwell, in as much he survived being mugged by Dirac and Feynman, is fine.
Not if we designate this new, faster light "C++".
Then the sums about "c" still make sense (mostly, for given values of "sense") but Science can still Be Done.
e.g. E=m(C++ - SCF*)
SCF - the Stevie Correction Factor needed to nudge C++ back towards c so the sums work again.
The constant is the sleed of light "in a vacuum". So, maybe we can have a negative vacuum to increase the speed of light.
OK - stupid - but since the constant governs everything we see,
A) I am not convinced their experiment will prove anything and
B) So what that it happened 13b years ago. How will that help anything today (like us getting to the nearest stars before we blow ourselves up).
or perhaps our current "vacuum" isn't a vacuum at all, perhaps it has something that we haven't detected yet, but this "something" was more/less abundant previously. Thus in the same way light is altered by the refractive index, this "something" also has a refractive index that is negative to our eyes (or rather our definition of a vacuum being 1 is wrong)
The Speed of Light in a vacuum is generally held to be constant - but what if the early universe was sufficiently dense that the SoL was reduced enough that matter could move faster than the SoL in that medium without violating our current theories?
Vacuum... the problem is that we really don't understand what we consider to be a vacuum actually is. Traditionally it's considered to be absolutely nothing, nada, nothing there at all. Unfortunately sub-atomic particles have a nasty habit of spontaneously forming in a vacuum can there truly nothing there because by definition they have to have come from something? Or is it the case that there is nothing there that we can currently observe and measure? in which case it's not unreasonable to assume that the speed of light may vary.
So we either have inflation... which would allow communication between primordial space and allow the flattening out of the background radiation...
Or we have the speed of light changing, which would have to have completely reduced itself to zero since, or low enough to be completely unmeasurable despite v = c / lamba being able to cause massive interference patterns at the slightest change
not really, it depends on what you mean by FTL. If it means that you set off at point A and got to point B before a beam of light from point A got to point B then you have travelled effectively FTL but that doesn't mean you went from point A to point B via the same course as the beam of light.
You still cant travel faster than light in a straight line but there are no real boundaries on (say) the theory of folding or wormhole or extradimensional rifts. By their nature these are outside our current laws and understandings.
Odd. When I was first introduced to science, and in the many years I worked in various fields, if an idea was proposed but hadn't been tested yet it was called a "hypothesis". Only AFTER it had been tested, and the tests repeated and verified, would it be called a "theory".
Based on this article, they haven't tested this hypothesis yet. Why does the article keep calling it a "theory"? In science, and presumably science articles, "theory" means "scientific theory" which in turn means "a tested and verified hypothesis".
Looking at the abstract (sadly, I've lost access to many research databases since changing careers. Fucking paywalls on publicly funded research, but that's another rant.) they don't seem to claim it's a "theory". They just claim to have developed a predictive model that might now be tested.
So either the scientists themselves are misusing the terminology in various interviews the author has seen and copied, and they're just repeating that. Or perhaps the author of this article is a scientific ignoramus with zero respect for proper terminology. Or perhaps the rules have changed since I learned this, and the anti-science frauds have won when they claim certain scientific theories are "only theories" and therefore equivalent to their completely non-scientific "theory"?
Which is it?
While I have a degree in physics, I not a physicist. But I find the current state of physics disturbing. For some it seems to have become a religion, where actual evidence is not necessary so long as you have an interesting hypothesis. And if it "proves" Einstein was wrong all the better.
While I'm sure Einstein didn't get it all right, so far his theories have proven remarkably resilient.
> But I find the current state of physics disturbing.
You may get this impression from encountering only mangled snippets of physics in popular media. Anything that involves hand-waving and Einstein being wrong has a chance being reported, no matter how crackpot. But that is something only a handful of people do. The second possibility to be mentioned is ‘It will make magically computers much faster’ or something similar, which is physics + material science -- lots of people do this and it is [usually] real science but then of course comes the nonsensical hype reporting. But even then, most physicists work in other subfields, and as there is little media hype there is also little bullshit.
Maxwell's equations wrong? Nope, they just mean that the electromagnetic constants such as permittivity and permeability of free space were different.
In fact, if space-time was of a very different density/size in the early universe I would be very surprised if the nature of "free space" was identical to now. Its just that physics has always assumed that natural constants are, well, constant over time and space. While it seems a reasonable start, we don't have any direct way to verify that, so observations of things from the early universe are possibly the only way to tell.
Not being an expert, I try to think about this anyway...
If we think about the case of the "singularity" before the Big Bang, it seems likely that the laws of physics we see today would be totally inadequate to describe that universe.
If we think about the case of the "singularity" before the Big Bang, it seems likely that the laws of physics we see today would be totally inadequate to describe that universe.In BBT there is no before the singularity, only after. The universe (everything there is and ever will be) had no prior existence. Make of that what you will. BB theorists claim that the laws of physics only began to come into existence, one by one, after the BB commenced.
"In BBT there is no before the singularity, only after. The universe (everything there is and ever will be) had no prior existence. Make of that what you will. BB theorists claim that the laws of physics only began to come into existence, one by one, after the BB commenced."
I don't think anyone ACTUALLY belives this.
It's just convenient not to have to think about it.
I don't think anyone ACTUALLY belives this.Oh, but scientists tell us it's a "scientifically proven fact". Like "eggs are good for you" when I was a child. And then "eggs are bad for you" from my 20s through 50s. Now they are good for me again. And it's all scientifically proven. Only filthy rotten sceptical denialists refuse to believe absolutely everything scientists declare to be true. ;-)
"I don't think anyone ACTUALLY belives this.
It's just convenient not to have to think about it."
I believe it wholeheartedly. The idea that the Big Bang was the creation of space and of time has a simple beauty to it. Time as we know it began at the instant of the explosion of energy. Thus terms like "before" and (presumably) "after" become meaningless, since they are only valid terms with a frame of reference involving Time. There was no time "before" the Universe since there was no "before" for it be part of.
If you want to argue Cause & Effect, why not imagine running the film of the Universe backwards. As we approach the beginning of Space and Time, causes and their effects appear closer together, until at the point of the Universe's creation all Time and Space exists in a state where any cause and any effect take place simultaneously. So the Big Bang caused the Big Bang, since the Big Bang was the First ever Event.
So the Big Bang caused the Big Bang, since the Big Bang was the First ever Event.And this uncaused cause, was, as everyone agrees, God. To paraphrase St Thomas Aquinas ca. 1270 AD. And to be fair, was itself a paraphrase of what Aristotle wrote ca. 350 BC.
" The idea that the Big Bang was the creation of space and of time has a simple beauty to it. "
If the universe itself is created and then expanding into nothing, not even "space" existed before.
All the mass/energy of the uinverse where nowhere to be seen. Existed nowhere.
I still think that the "all came of nothing" claim is just a convenience and a way of avoiding to admit that we have no clue.
> I still think that the "all came of nothing" claim is just a convenience and a way of avoiding to admit that we have no clue.
Meanwhile, I consider it a tantalising, but otherwise irrelevant, distraction. A barrier beyond which we cannot possibly see. We don't have a clue, and we can never have a clue. So what's the point in worrying about it?
What was "here" "beforehand"? Could be anything. Another universe, noise and light, or just turtle-porn all the way down...
We're on a hard disc that got reformatted >13Bn years ago. Good luck finding your old files from before the reinstall... (Maybe we should be scouring the universe for bad sectors that have been mapped out beforehand.)
When I was a nipper there were four stages: observation, hypothesis, experiment, conclusion. It seems that here they have an observation (odd behaviour in CBR), a hypothesis (c perhaps variable after all), are designing an experim,ent and that will lead to a conclusion (of some sort - possibly that the experiment was flakey)
I think 'theory' is just a nice easy-to-understand synonym for 'hypothesis' to make life easier for Daily Mail and Express readers, whose difficulties with clear analytical reasoning are long-proven.
AFAIK inflation is an explanation for the way in which the early universe evolved into what we see. It does not emerge naturally from the standard model or general relativity. The possibility of a variable-over-time speed of light can offer alternative solutions to the horizon problem. However, there are several predictions which emerge from inflation theory and have been confirmed so as well as the proposed test variable speed would have to generate some explanation for those results. If not we could have two incompatible hypotheses and a lot of astrophysicists pulling their hair out.
Space expanded incredibly quickly for a very short time with a constant speed of light (insert handwaving explanation here...)
The speed of light changed rapidly over a very short period of time with a steady expansion of the universe (insert handwaving explanation here...)
Meanwhile the universe appears to be expanding at an ever increasing rate (mumble, mumble, dark energy, mumble, mumble).
Maybe we really just don't have a clue!
"Meanwhile the universe appears to be expanding at an ever increasing rate "
Maybe the accelerating expansion was all a mistake, down to there being insufficient observational data at the time. Professor Subir Sarkar of Oxford University's Department of Physics has used the larger dataset that is now available. He suggests that "the apparent manifestation of dark energy is a consequence of analysing the data in an oversimplified theoretical model."
I'm an idiot.
If it were me, I would look at that idea and say : "okay, so it might have been different. No way to prove it, why bother ?".
But these guys went on and not only wrote out their theory but claim to have a test that can prove it. And they're putting that up in front of a community of people who are very capable of putting said theory to the test and either thoroughly trashing it or conclusively proving it, or somewhere in the middle where proof is not definite but could be possible if some more intelligent people could be found to find out.
And I, the caveman, can only look on and wonder who will bring an answer to these questions while all I'm capable of doing is wash the dishes.
Kudos to these enlightened people who have questions that I couldn't even begin to ask myself. Whatever the answer, you will have improved Humanity's understanding of the Universe, and that's more than I will ever be capable of.
a community of people who are very capable of putting said theory to the test and either thoroughly trashing it or conclusively proving it, or somewhere in the middle where proof is not definite but could be possible if some more intelligent people could be found to find out.Scientific theories cannot be proven; they can be corroborated, but that's not proof. Proof is only available in the domains of mathematics and logic.
But these guys went on and not only wrote out their theory but claim to have a test that can prove it. And they're putting that up in front of a community of people who are very capable of putting said theory to the test and either thoroughly trashing it or conclusively proving itName one scientific theory that has been "conclusively proven". Consider the following syllogism:
If my scientific theory is correct, then I will make certain observations.
I do make those observations, therefore my scientific theory is correct.
Now let's replace the premisses with different premisses.
If Hilary is pregnant, then Hilary is a female.
Hilary is female, therefore Hilary is pregnant.
This fallacy is known as affirming the consequent. You can believe as fervently as you want this this is a valid argument, but it's not.
Karl Popper proposed the following syllogism that is valid:
If my scientific theory is correct, then I will make certain observations.
I do not observe what my scientific theory predicted I should observe.
Therefore my scientific theory is incorrect.
Just as no amount of observing pregnant females can prove all females are pregnant, there will never be a sufficient number of corroborative observations to "conclusively prove" a scientific theory. We can only disprove a scientific theory.
Changes in gravity travel at the speed of light.
Newton assumed that gravity travelled instantly (he didn't know light had a finite speed) which meant that same classical astronomy observations didn't add up.
When you assume that gravity travels at the speed of light it all works out. Which was the reason for trying to measure a speed of light and was done succesfully pretty much at the end of Newton's life.
Mercury's orbit not matching Newton has nothing to do with the speed that gravity may, or may not, travel at, but everything to do with time dilation close to a massive object like the sun.
Until we can accurately correlated gravity waves (only recently detected) with an optical signature, etc, we won't have any evidence to corroborate the speed of gravity.
To be fair, there are plenty of particles that can go faster than the speed of light in a particular medium, but there are no experimentally observed particles that exceed the speed of light in a vacuum.
The refractive index of a transparent medium is simply the ratio that is speed of light in a vacuum divided by the speed of light through that medium. So light is slower going through glass than a vacuum - the speed used for light going down an optical fibre (like submarine cables) is approximately 2/3 c, so the refractive index is roughly 1.5 (For water, it is roughly 1.333)
So, what you need is a particle that goes through glass faster than light goes through glass. Or one that goes through water faster than light goes through water. it turns out that the speed at which particles are ejected from atoms during radioactive decay can easily exceed the speed of light in glass or water.
So locally, while in the glass or water, particles ejected from a radioactive atoms can exceed the local speed of light (usually electons ie beta-decay). Simplifying a bit, electrically charged particles going a medium faster than light emit light - called Cherenkov radiation, which appears as a blue glow. This is why you get the blue glow around reactor rods operating in water-cooled research nuclear reactors.
"All FTL particles are hypothetical and in theory can't go slower than "c", if they did exist."
Not exactly. FTL particles could theoretically travel slower than c as well as faster. They just can't travel exactly at c, meaning they couldn't slow down through c to subluminal speeds. If they had a way to instantly change speed without going through all speeds in between then they could travel slower than c as well as faster.
light can be "stopped" in 0k rubidium condensate (well, held in an excited state). That being said, your hand would also have issues in the same.
superluminal effects can only be observed and it is probably the observations that are incorrect (incorrect as in there are ways to explain why they appear to be superluminal). Ironically, one of the effects is the expansion of space itself, some objects are moving away from us as at an observable "greater than c"
I thought the whole point was that a tachyon is the name for a particle that travels faster than light. But none actually exist.
Cherenkov radiation is shed by when a particle that would have been travelling faster than light in the medium it finds itself in suddenly hits reality face first. Energy is shed, lovely blue glow, particle travelling at a valid speed, causality is preserved.
The main idea I've read over the years is that the speed of light is constant throughout space but not over time. In other words it is the same everywhere but that "same" value has been decreasing *over time* from an extremely large multiple since the universe came into being/inflated/rebounded/was created/whatever your guess is.
A much higher speed of light in the past would enable the expansion of the universe to have occurred very much (hugely in fact) quicker. If so then the universe could be fantastically younger than currently thought as it's size (which is based partly on today's light speed "constant") affects calculations of it's age and assumes the same speed of light over time.
In addition, there are many dating methods that indirectly include the speed of light in their calculations and whose results could be off by an order of magnitude on an exponential scale projected backwards over time.
These are only hypotheses but if true then the simple fact of a vastly higher speed of light in the past could lead to a young universe with a young Earth and a young fossil record.
In the ultimate, it is very hard to distinguish distance from time. You can say that distance is something that is defined by "how far" something goes in a given time or time is a measure of "how long" something takes to go a given distance. Even things like atomic clocks fall victim to this since they rely on counting the number of oscillations of something that is produced by a transition of the wave function of an electron through a distance. But how long is the distance? Well it is one that produces a given number of waves in a given time. And there you are back to ground zero. About the only potentially independent definition of length is the Plank length, but even there, it is defined in terms of time.
I would continue at length, but I do not have the time.
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The currently-accepted age of the Universe is 13.7 billion years. The age of the Earth is given to be 4.5 billion years. The Earth thus came about in the last third of this Universe's current existence.
If the speed of light was different in the early days of the Universe, it might indeed mean that the Universe could be younger than is currently accepted, but I doubt that would change its age by 50%. It would likely be a lot less than that, if we can find a way to prove anything.
As far as the age of the Earth is concerned, nothing about the speed of light will change anything because the age of Earth's crust is not determined by light but by the degradation of uranium into lead which is a fixed constant. So no, whatever happens to the age of the Universe, the Creationists are not going to be able to twist that into a 6,000-year-old Earth.
1. Design and build a Time Machine.
2. Design and build a Comprehensive Test Harness for the Time Machine.
3. Test the Time Machine.
4. Identify and fix bugs in Time Machine, based on results from running the Comprehensive Test Harness.
- Note to self: depending on the bugs you find, this could prove catastrophic
5. If you recovered from , and are still around, go back to . Repeat until there are no bugs.
6. When the Time Machine is bug-free, travel back in time to the early days of the Universe.
7. Measure speed of light.
8. Come back.
9. Compare results from  with today's speed of light.
10. Let us know when the results of experiment proposed above are published.
No this is how you do it:
1. Get into the time machine you built in step four, taking the plans with you
2. Travel back to the beginning of the universe and measure the speed of light
3. Return to your own time frame, stopping off on the way to drop off the time machine plans to your earlier self
4. Build a time machine
Good idea, but best to drop your bug testing loop into the time travelling loop.
For example, 1) Design and build a Time Machine.
2) Send time machine to the past at a chosen time, if it arrives with bugs, fix as many as you can and send it back further.
3) Once there are no bugs, send it back to the present (1 second in the future from the time machines new perspective).
4) Do your experiments.
This means you get a bug free time machine rather quickly. Now if teaching past yourselves how to bug fix the machines is an exponentially increasing problem (perhaps the laws of physics trying to keep hold of your device!) then just send it to the future for them to bug fix instead...
The correct phrase is "speed of light in a vacuum". But there is no perfect vacuum. Space is full of plasma. Even the least dense areas of space are not a perfect vacuum. So is it possible that a photon could travel 14 or so BILLION years and not encounter some form of plasma ion? And even if it doesn't collide head on with an ion, wouldn't the charges involved modify the trajectory, however minuscule that modification might be? And wouldn't multiple interactions invoke multiple modifications?
And then there's all those neutrinos. We are told billions of them are passing though out bodies every second. We are also told they "rarely" interact with matter, but "rarely" is not "never".
"But there is no perfect vacuum"
That's what I was wondering too. Is the speed of light in intergalactic, or intergalactic-family space faster than in interstellar or interplanetary space where the local density of space is likely to be different?
It ain't my field so I have no idea if I'm talking out of my arse.
Is the speed of light in intergalactic, or intergalactic-family space faster than in interstellar or interplanetary space where the local density of space is likely to be different?I suspect that you'll have to await actual in situ measurement if you are an Aristotelian. If you're a neo-Platonist, it's just a matter of contemplating your navel and then plucking a number out of your arse ;-)
The only thing that can modify the trajectory of a photon is what is called gravitational lensing, and apparently you need a cluster of galaxies to obtain that effect.
So no, I don't think individual plasma ions are going to have an effect on the trajectory of photons.
Interestingly though, we are taught that light (ie photons) "bounce off" of objects, which is what allows us to see them. So you need entire galaxies to bend their trajectory, but a grain of sand can send the off in an entirely different direction. I still have trouble wrapping my head around that one.
There is a theoretical problem/puzzle on how much light you would need to optically lens light via it's own gravitational pull (from it's own energy).
I'd have to look it up again, I cannot remember if it was considered impossible, impractical or if it would happen. Does the early universe have that high a concentration of light/energy? I'd assume no due to expansion and it not becoming a singularity.
"You need entire galaxies to warp spacetime. Light just goes straight"
You do know that one of the first tests of GR was the 'bending' of a star's position by the sun
"The only thing that can modify the trajectory of a photon is what is called gravitational lensing, and apparently you need a cluster of galaxies to obtain that effect"
I have this miraculous device called a 'mirror' that seems to do the job pretty well...
I have this miraculous device called a 'mirror' that seems to do the job pretty well...Trajectory: "The path of any body moving under the action of given forces; by many modern writers restricted to that of a body not known to be moving, like a planet, in a closed curve or orbit; esp. the curve described by a projectile in its flight through the air."
If you have any evidence that the path of photons from your "miraculous" mirror are travelling in curves, please present it. You could be in for a Nobel prize!
A hypothesis is a theory without supporting evidence.No. A scientific hypothesis is an explanation based on limited evidence. A scientific theory is also an explanation, but since it's not possible to amass all possible evidence, is also based on limited evidence, just not as limited. IOW it's not worth making a distinction between hypothesis and theory in science.
It's widely understood that relativity claims that c is a constant, or put another way, the axiom holds that there exists a velocity that is constant in all reference frames: thus 'exceeding' the speed of light (at least for objects with mass (or in the case of photons, with momentum) is not so much impossible, but meaningless. Like 'biting your teeth', or 'measuring' the position and velocity of an electron simultaneously.
What isn't widely known is that the speed of light can be derived from first principles, and had been from the 19th century, from the permittivity and permeability properties of the vacuum.
Since the vacuum is reasonably supposed to be invariant itself, permittivity and permeability should be fixed and so the value of c (in vacuo). But suppose during the earliest periods of the space-time expansion, those two properties were somehow... what?... concentrated? Velocity of a wave in a classical 'medium' is a function of its restoring-force, and if the restoring force is somewhat 'enhanced' by the 'concentration' of the two properties, and excusing my single-quotes, then perhaps the value of c might have been greater in the earliest universe.
Also excuse my calling the spacio-temporal manifold a 'medium', but it seems a fundamental universal in classical, relativistic, and quantum domains is the oscillatory phenomenon required by Newton's classical dynamic of displacement and restoring force.
"It's widely understood that relativity claims that c is a constant"
Not just Relativity. It comes out as a constant in Maxwell's equations, for a vacuum. A medium allows for slower propagation of light, radio, magnetism, electric fields. A coaxial cable slows radio waves, like fibres slow light. Or PCB traces on a multilayer board slow the signals.
Einstein was understandably pleased when he studied Maxwell's work.
I can think of at least one way the speed of light could have exceeded the expected speed within the early universe... if it was re-emitted but due to time length/iteration/quantum uncertainty limits did not interact as often with particles. It could have "skipped" particles, due to them being so close together? Then it would not be limited by re-emission as it is now in water/glass etc... due to the early universe being so dense.
Though it may just be me who is dense.
During the inflationary period the infant universe had to expand very much faster than the current speed of light. However, the universe was so tiny at the time that at the end of inflation it was only a few centimetres across (So I understand from reading, I don't actually have the ruler with the markings.)
The infant universe consisted, too, of nothing but radiation; so the workaround seems to be that it's OK for spacetime to expand faster than the speed of light. Of course, there was no information in the infant universe, so the rule that information cannot travel faster than light, at least, wasn't being violated. But if it was expanding at the current variable speed of light, different parts would still not be in communication with one another, so anisotropy would still be possible.
I don't actually see the problem if the speed of light is related to, say, the logarithmic scale of the universe, since this has effectively been more or less constant for a very long time.
But IANAP, so perhaps someone who is will enlighten me.
Time didn't exist before the big bang, and if the clock didn't start ticking at the very moment matter came into existence, then acceleration would have been infinite and the entire universe scattered to the ends of eternity.
Perhaps there is a force that we have yet to get our heads around, one that isn't constrained by time, and has been expanding from the start at a constant rate, defining the limits of our universe and thus in the moment time didn't exist, act as a break to stop the universe expanding into obscurity.
So. In the beginning the universe expanded at an infinite rate, but infinity was bounded by a force that expanded at a more casual pace, let's say for arguments sake, speed of light squared,
Matter would accelerate at infinite speed from the source of the big bang, yet not breach the bounds of this new force, which I shall name Reality. The effect wouldn't be unlike a balloon inflating, with matter and energy colliding together at this boundary for an eternity and thus evening out any disparities, to create the more or less homogeneous place we see today. Once time came into being the whole process got a little more sedate, and the "inflationary" period came to an end.
Reality is now defining a universe many factors beyond the furthermost particles that we consider to be the boundary, and seeing as Trump has just been elected, proof that is of no relevance to today's universe.
and the link is wiki, but light wasn't around until after inflation
Which would mean that there was no light until the first stars lit 362 million years after inflation and therefore no speed of light. Light is the big boy in measurement terms now but there are 400 million years before it was around and 20 million years when it was openly defied by our wonderfully complex universe.
It seems to me that the universe from big bang to end of inflation existed only as a large bowl of quantum 'soup' that had no respect for Einstein, Maxwell, Lorentz or any one else. Someone getting their minds around what that soup consisted of and it's behaviour is probably not happening in whatever is left of my timeline.
There was plenty of light in the earliest stages of the universe (in fact it was mostly photons) but they were affected by the density of mass. It wasn't until approximately 380,000 years after the Big Bang that the universe had cooled enough to allow atoms to form, releasing the photons we see today as the CMB from the sub-atomic soup.
Yep, since the 1980's the metre has been defined as the distance that light travels in a vacuum over 1/299792458th of a second. This makes it easier to derive your own local metre without having to traipse over to Paris to check your metre rule against their 'standard' metre rule. A side effect of this is that the speed of light is fixed at exactly 299792458m/s.
The distance from the North Pole to the Equator via Paris was originally defined as 10,000 km. Then it was based on a standard pole, then on the wavelength of a particular type of light. The number chosen for the speed of light was used to keep it constant with previous definitions.
The distance from the North Pole to the Equator via Paris was originally defined as 10,000 km. Then it [the metre] was based on a standard pole, then on the wavelength of a particular type of light.
Those who are old enough to have learned Imperial units at school will be delighted to discover that the metre was at one time defined in terms of the rod, pole or perch.
The rod or perch or pole is a surveyors tool and unit of length equal to 5 1⁄2 yards, 16 1⁄2 feet, 1⁄320 of a statute mile or one-fourth of a surveyor's chain. The rod is useful as a unit of length because whole number multiples of it can equal one acre of square measure.
"This makes it easier to derive your own local metre without having to traipse over to Paris to check your metre rule against their 'standard' metre rule."
"Easier" for some value of easier. The kit required costs a bit more than the return business class fare to Paris from anywhere on Earth, with taxis and hotel bill added. The problem would come when you turned up and asked them to let you compare your rod to theirs. This is a case where actually using the primary reference (and transporting yours) is likely to affect its value.
The problem would come when you turned up and asked them to let you compare your rod to theirs.If you were English and turning up to compare your rod with their French rod, surely the problem would be the impossibility of the English rod being anything other than inferior. Les Albions perfides and all that.
Whether or not the speed of light is, was, or will be faster or slower than it is "now", it's kind of like saying time passes slower or faster than it used to--from our perspective, within the system, it's consistent, however much the universe's expansion is accelerating. Kind of like if you were an AI and someone kept changing the clock speed of the system you were running on--without anything external to observe, you'd never know.
It's great that someone devised a brilliant experiment to test this, but I always look at these things from a perspective of "can this be exploited for something cool?" such as FTL or time travel. Unfortunately for now it still appears that you can't win, can't cheat, and can't quit the game. (unless you die)
Of course Einstein was wrong.. but the Big Bang theory is wrong too!
There is no fixed speed of light. The fact that complex mathematical models and equations seem to work correctly with a fixed speed of light at least here on Earth mean absolutely nothing.
Any science claiming to have found "the laws of nature" is deadly wrong from the start.
A mathematical model can seem to be perfect and a law with limited knowledge in a limited area but it doesn't mean that is the law of all universes and it works everywhere.
Possibly not being constant, and no one has mentioned Neal Stephenson's Anathem?
Some day i want to have a meal with that guy.
Recently read that -- there are a couple of assumptions in there that make the physical world shimmer when you read them and the math sets in.
Anathem= Concepts from Roger Penrose's books on math: Eg. "road to Reality"..
YUM, first 16 chapters is a review of Math Analysis to enable reading the rest of his book..
caveiat= had to read the book 3 times, First as a SF Novel, Second quickly to see what was covered, Last to actually answer his test questions and get something out of this exquisit book.. RS.
A gedankenexperiment that's perfectly safe to conduct at home.
Imagine you have a powerful torch like the new LED torch I just received from China. You can focus the light beam such that it's a very small spot onto a nearby wall. Imagine the wall is very long, perhaps ininitely long, but that's not necessary for our purpose. Gradually rotate the torch on its axis so the spot of light moves away from you.
As the beam of light comes close to parallel with the wall, the spot of light will be travelling very fast indeed. Eventually, with a minuscule change in angle, the spot of light on the wall will be travelling faster than the speed of light. Or will it?
Note well that the amount of energy being expended to merely rotate the torch here is very small.
"Eventually, with a minuscule change in angle, the spot of light on the wall will be travelling faster than the speed of light. Or will it?"
The fallacy here is to see the lightbeam as some kind of rigid rod that instantly moves as you move its base.
Think of it instead as water coming out of a hose. As you move the hose, the water bends. So the spot, in this case, will not move instantly at all.
Before the spot "moves" (it's actually constantly a new spot), light has to travel all the way from the torch to the wall.
Well, that's my layman explanation anyway.
@ anonymous boring coward
There's no fallacy here. A fallacy is a deceptive or misleading argument. You did see the problem though. The spot of light we see is not an object; i.e. it possesses neither mass, nor extension. It's a good one for the pub on Friday night. I usually explain the problem by analogy with a machine gun, rather than a stream of water though. You did rather better than a physicist with a PhD I know :-)
You cannot rotate the torch faster than the speed of light. The emission of light is at the speed of light.
So you effectively have a spiral of photons/waves travelling away from you at the speed of light in a spiral (if you span 360 and not just across the wall).
The question is, do any of those photons/waves appear to be travelling faster than light from any perspective/trajectory? Einstein would say no and I assume it holds. I'm just not smart enough to do the maths just now though.
So you effectively have a spiral of photons/waves travelling away from you at the speed of light in a spiral (if you span 360 and not just across the wall).I think you are missing the point. Imagine that instead of a spot of light, that it's a projected image of Phar Lap winning the Agua Caliente Handicap in 1932. Clearly it's not Phar Lap, nor is it 1932 and Phar Lap, while a very fast horse indeed, certainly never ran faster than the speed of light. What we are seeing is in our mind. It's metaphysical, not physical. As I said below, possessing neither mass, nor extension.
You are correct in your instinct though. There is no physical "thing" travelling faster than light.
I have even better gedankenexperiment for you.
Imagine giant scissors hanging in the vacuum of space. They can be as large as you like, even greater than our Galaxy. They are as rigid as baryon matter lets us but it is no problem as they are powered by rocket engines ingeniously placed along them. We can program them to make the scissors cut as fast as we want. The only limit is that the points have to move slower than c.
It is easy to calculate that the Space Scissors can cut much faster than light without breaking relativity or causality. The engines have to be programmed before the cutting stats and the signals along the scissors cannot travel faster than light. But if you start with sufficient time to spare you will succeed in all the segments of the scissors moving in perfect unison.
So it is possible to create an effect moving faster than light without transferring any information with super-luminous velocities.
Lots of the constants just come from the (best current knowledge) maths looking at things as they are now.
e.g. If I had lifespan equivalent to the universe, If I was "sampled" in the human era, things like my waistline, blood pressure, time to run 100m etc would be a lot worse than when I was in my prime (which, on universe timescales would be billions of years earlier), but my current stats would appear constant over the (relatively tiny) timescale used.
Querying constants is nothing new, there's always been people asking "how do we know this constant has always had this value"
.. I remember, as an inquisitive / PITA schoolkid (delete per your preference) asking my physics teacher that at comprehensive (forgotten which constant my question was referring to, might not have been c) and getting the (honest) answer of "we don't".
A huge amount of our physics knowledge is just best guess theories, there's a long way to go before we can really explain the universe with any half decent chance of accuracy.
Theres so many ideas being proposed in theoretical physics (TP), it only tends to be odd one or two that get much media attention though.
It's very difficult / impossible to experimentally prove / disprove an awful lot of TP stuff, so it's an ideas churning out industry (though at least this is potentially disproveable)
Disclosure: I studied some physics / astrophyics to university level but do not work in physics, but I still have an interest & read about the subject (instead of grappling against a crossword setter, try and pit my old addled brain against some hard maths & odd concepts)
So all our efforts to measure the age of things could be incorrect as well? Maybe the earth is only 6000 years old after all.
Which is co-incidentally where I first heard this suggestion:-
Perhaps it's worth checking these chap's agenda before putting too much effort into this?
The big bang was happening 'in parallel' throughout the young universe. If you want consistency between one end of the universe and the other, the light does not need to traverse the entire distance to create adequate influence and uniformity -
For example, if light could only reach 25% of the way across the universe, then every point in the universe could influence a large part that almost totally *overlapped* its neighbour.
As a result there would be a pressure to achieve local uniformity where local was actually something that was interlinked across the whole universe.
Anyway, my feeling (and no, I don't profess to know) is that you don't need to address the horizon problem to explain overall uniformity in a system, particularly where that system is undergoing the same basic process throughout.
Speed of light is our reference since the formulas make out to be simpler that way. It is definitely possible to set up formulas where a changing light speed over history is used.
To explain big bang and inflation we could see it as light speed dropping while the universe stay att the same size. Inside the universe a reduction of light speed would look exactly same as inflation since that is what we use to measure distances.
For me that way of looking at it is useful to understand how big bang could happen everywhere. It did not happen in a single point from which it expanded.
Since It only changes the point of view, I can not imagine any experiments that could prove it one way or the other. What could happen though is that with more observations more complicated formulas are needed to explain them and some day using a variable light speed would make a less complicated model.
For now Ochams razor say light speed is constant.