COVID-19 is pretty nasty but maybe this is taking social distancing too far? Universe may not be expanding equally in all directions

The universe may not be expanding at the same rate in all directions according to a study backed by the European Space Agency – a possibility that has left cosmologists asking themselves some serious questions. The cosmological principle rests on the idea the universe is both homogeneous and isotropic. In other words, it looks …

[Anonymous Coward]

Is it relative to the observer?

If you turned your back on them, and looked in the opposite direction at the sky at the other side of the planet, do you find the opposite effect? Instead of brighter you find darker, instead of darker you find brighter?

Can you find a maximum and minimum for this, and are those maximum and minimums in opposite direction relative to us the observer? i.e. You found ~30% discrepancies, can you find larger discrepancies? As you refine the maximum and minimum does it more and more form a line through the earth? i.e. an effect relative to the observer here on earth?

So you've likely found an effect similar to the CMB cold spot and its ripples, and if you found the opposing effect on the other side relative to us, then you would confirm the effect is relative to the observer.

[Anonymous Coward]

Re: Is it relative to the observer?

The article is somewhat confusingly worded: the people have observed an effect which is dependent on which way you look. 'Which way' being relative to some stable reference frame though, not, say, 'east, on Earth' which rotates once a day.

[bombastic bob]

Re: Is it relative to the observer?

assuming 'big bang' which is likely...

It started at a single point, and everything expanded from there. Using relative velocities it's possible to (more or less) guess where that was.

However...

you have to consider one important fact: When you have an explosion, the energy that is transferred to the things that fly away is not uniform. PLUS, you have momentum and kinetic energy to deal with. momentum (total momentum) is conserved. Kinetic energy is also conserved, and the mass of something is inversely proportional to the square of its resulting velocity [with kinetic energy as a constant in this case]. This is very important for inelastic collisions... which might emit gamma radiation to make up the difference.

Saying that more simply: heavy things won't be going as fast as lighter ones, and if one side has more or less heavy things than other sides, the lighter things on that side may also have different velocities (due to momentum conservation).

So none of this should be a surprise. In fact, 'explosion' kinda implies chaotic results, doesn't it?

It DOES suggest that big bang produced particles of varying mass, from my perspective anyway.

[Gene Cash]

And below this article is one with the headline:

"Cosmology is safe and the Universe is one giant version of the Barbican

Whichever way you look it's all exactly the same, boffins confirm"

[Tom 7]

We're living in a Barbie Universe!

[Eddy Ito]

It's worse than that, we're exactly in the middle of that universe. If you could look forward and see the edge of the universe it would be ~13.8 billion light years away and if you turn around 180 degrees and could see the edge of the universe in that direction it would also be ~13.8 billion light years away. The same would be true if you look up, down, left, or right the edges of the universe would all be ~13.8 billion light years distant. Naturally, the same would be true regardless of where in the universe the observer is. Just proof that we're all in that same Barbie boat together.

[Wzrd1]

It's worse than that, we're exactly in the middle of that universe.

It's worse than that, really. *Everywhere* is exactly in the middle of the universe.

Meanwhile, this could be from magnetic polarization or even gravitational effects of an extremely large object/structure, the sample size is way, way, way too small.

[BrownishMonstr]

It's obviously because of 5G.

BURN THE MASTS.

[KittenHuffer]

I 'Upped' you cos I thought it was funny, NOT because I agree with you.

You should have used a joke icon cos I'm sure there will be those that 'Down' you cos they think you're serious!

[Sgt_Oddball]

This the register...

For the removal of doubt, sarcasm should always be assumed as it is the primary communication method around here.

Also, you can tell the sarcasm is implied as otherwise less straight forward language would have been employed as well as a more thorough strategy than just burning the towers. Say immolating the towers and basestations, extra points for destroying upstream fibre optic nodes.

Points deducted for attacking staff/firefighters/leaving the whole lot salvageable.

[Peter2]

Re: This the register...

Can I suggest that people refrain from posting even what our industry calls upstream nodes or where they are always located?

The sort of ignorant dick who understands the logic of "a mobile phone masts transmits radio waves, which is radiated energy (OMG; RADIATION! BURN IT)" probably understands just enough to be dangerous and no more.

If somebody here posted industry standard names of descriptions of those upstream nodes then it's possible that idiots might be reading this site and could use information almost everybody reading this knows to google the locations of the upstream nodes and then wreck large parts of the countries internet and telecoms connectivity in the name of protecting people from radio waves.

And yes, that's as stupid than trying to ban water because somebody pulled out the old dihydrogen monoxide scare story but it is unfortunately about the level of general education that most of the public have, excepting that they think because they can google something they are now the worlds foremost expert in it.

[Anonymous Coward]

Re: This the register...

I might like to first make a point of whilst this site proudly has a redtop, the IQ of readership is normally assumed to be into 3 figures thus making it somewhat far and away departed from the regular gutter press who's readership would revel in setting fire to stuff (if only because it meant they'd finally managed to work a lighter).

They can Google this site all they want but the likelihood of them firstly finding the site (based off a Google profile showing a preference towards knuckle dragging and smashing rocks together) is somewhat remote. Even more that they'd read and furthermore understanding anything past the first paragraph is fleetingly remote... Final step would be to enter the bearpit comments section.

Or.. Or do you know something different from the rest of us here? Enquiring minds and all that..

[Blitheringeejit]

Re: This the register...

Your intellectual arrogance might carry a little more weight if you demonstrated an ability to use the apostrophe correctly. "Who's" above is linguistic knuckle-dragging.

[Anonymous Coward]

Re: This the register...

Ahh, apologies for that slip of the mobile keyboard.

Blame a mixture dyslexia, council estate public education and lack of effort in the written form caused by pure apathy on my part.

Next you'll be writing in the corrections email over gross over-use of the grocer's apostrophe...

[sean.fr]

Apostrophe Rules

Thats a bit strong.

To quote John Richards, the founder of The Apostrophe Protection Society:

"We, and our many supporters worldwide, have done our best but the ignorance and laziness present in modern times have won! "

If people are doing it "wrong", in large numbers, wrong becomes acceptable. Few of us are confident in the Apostrophe rules, or particularly care.

This is no Académie Française for English. In school there may be a school exam board. But this is not school, it is an informal context.

If you want a spell/grammer button added to the posting screen, I am Ok with that.

[ILLQO]

Re: Apostrophe Rules

This bit of high brow sarcasm, useless argument, and general comradeship building between geeks is one of the reasons that I have fallen in love with this site over the last 2 years.

[Tom 7]

Re: This the register...

Sarcasm? Pphhth!

[Danny 2]

I wouldn't even have thought to burn down a mast, I would have just pulled it down and smashed the gear. Kudos to the brains there taking out all the 5G and 4G and 3G kit. That will save our emergency services a lot of calls in these covid times.

Joke Icon.

[Steve K]

Timecube

It's tIMEcUBE

[Anonymous Coward]

Lets play 'suppose'

1) Suppose that the mechanism of motion of light, and the mechanism of motion of matter is one and the same.

2) So the electron apparently dancing around, is actually just the same motion as light dancing around, it is dancing in the same field, only the electron returns to the same place over and over again, whereas the light traverses that field. It's a different dance steps, but the beat is the same.

3) But now due to 2), the size of the electron is related to the speed of light. If this field was 2x bigger, then so would the electron be 2x bigger and light would travel twice as far across that axis too.

4) And when you measured the speed of light with a electron based measurement, if the speed was 2x faster, and the electron is 2x longer, the you would get the same measurement. It would appear to be a constant.

5) Which implies the speed of light is not a constant, but when you measure it, you will always get the same answer if the equipment, and the light, are subject to the same field motion, you'll simple measure the same ratio.

So light comes across the galaxy across some sort of unspecified field. That field won't be orientated relative to us, we are not special, and yet in any direction we measure light, it appears to be coming at us at the same speed, as if the field IS somehow orientated relative to us. So you can see how 2) is the cause of our confusion.

So, lets suppose that light isn't a constant, and its only a constant ratio with respect to the equipment measuring it. You'd expect to be able to find anomalies like this. Estimate things by red shift and you'd get one result, estimate it across our viewing axis, and you'd get another.

And wouldn't you then expect those anomalies to be the opposite when viewed from the opposing direction? i.e. they'd be relative to the observer.

You might dismiss these as measurement errors.

But then again, a penny might drop.

[KittenHuffer]

Re: Lets play 'suppose'

Your number 1 supposition is flawed.

Particles with mass are affected by the Higgs field, particles without mass are not. The mechanism of motion of both is different.

Please correct this flaw in your argument and then see how this affects the rest of your post.

[Anonymous Coward]

Re: Lets play 'suppose'

Causality and motion are both limited by the speed of light limit. However, that is different from the "speed a photon travels at" effectively.

Either way, without data or experimental process and tests, and musings are chasing after the wind on ones dreams.

So while a theory of quantum gravity, or a theory of quantatised movement/inertia/etc could be proposed by the OP, it's not wrong because it's wrong. It's wrong because it does not match the data or observations or experiments.

Nothing wrong with thinking up new ideas for new tests. Very much wrong for thinknig up new fairies to live in the pot of gold.

[Brewster's Angle Grinder]

As always, neutrinos are left out the mix.

Point 1 is the only point that's fine - at least as I parse it. Photons and other particles experience identical "mechanisms of motion" (geometry) which is why light bends round stars and black holes. But, obviously, without a quantum theory of gravity we can't be certain.

[AlanS]

Re: As always, neutrinos are left out the mix.

IIRC, photons and matter are different under gravity. That was why the eclipse experiment was done during WW1, to check the displacement of star images near the sun during a total eclipse. Einstein's general theory of relativity predicts twice the displacement of Newton's theory of gravity.

[bombastic bob]

Re: Lets play 'suppose'

yeah, light motion occurs at C and is more of an energy field only where the mass is implied [or imaginary, based on what math you like to use], whereas particle motion has REAL mass and is always less than C.

Momentum and kinetic energy still apply in both cases, of course, but when you travel at C you become light, and so the rules are a *tad* different.

Light has 'rest mass' and is affected by gravity. Einstein proposed it and it was later proved.

Particles without mass like neutrinos are not *entirely* massless, but their probabilities of interaction are so small that they might as well have no mass [for the most part]. But they still have energy, and therefore velocity, and therefore momentum, so go fig.

"not such an easy thing" to explain, eh?

as far as sub-atomics go, there may be actual massless ones, but without mass they can have no momentum, so how do we detect them [even theoretically] since there is no kinetic energy either...

[detecting a mismatch in momentum would detect 'undetectable' particles]

there are other balances, too, like particle vs anti-particle.

[Pascal Monett]

Re: Lets play 'suppose'

It's the Universe that is getting bigger, not the particles.

If everything including matter was getting bigger, then we wouldn't be able to notice.

[Rich 11]

Re: Lets play 'suppose'

Lets play 'suppose'

Let's not.

[EBG]

Re: Lets play 'suppose'

Word for word my intended response, but you beat me to it.

[bombastic bob]

Re: Lets play 'suppose'

in reality electrons exist in a probability 'cloud' that (as I understand it) exhibits some "now you see it now you don't" behavior as well as other unpredictability. My opinion, it's waltzing about through different dimensions, including time, just to make quantum mechanics more difficult for us, heh.

nuclear reactions are all about probabilities, so it's not surprising.

[A Non e-mouse]

It's because in the direction of Earth's orbit the Aether is being compressed, so making it denser and harder for the light to travel through and behind the Earth, the Aether is thinner so it's easier for the light to travel through.

SImples.

[Anonymous Coward]

If you look at the picture carefully, it's obviously because the cosmic chicken is developing in the cosmic egg,which is why the middle bit is yellow.

[Stoneshop]

the cosmic chicken is developing in the cosmic egg

The deeper into space you look, the farther back in time are the things you observe.

So it's more likely to be some saurier, or even one of its ancestors.

[KittenHuffer]

This needs a bigger better study

There is a phrase coined by Carl Sagan that "Extraordinary claims require extraordinary evidence". And since the current cosmological thinking (and prevailing evidence) is that the Universe is flat to within 0.5% then this claim needs to be supported by some pretty extraordinary exidence, which doesn't appear to be there yet.

Summary of the current cosmological thinking:

https://medium.com/starts-with-a-bang/ask-ethan-87-the-shape-of-the-universe-bce004916a33

If the Universe wasn't expanding evenly then that would suggest that it isn't flat (to within 0.5%) and I would have expected this to show up in the analysis of the CMB.

[bazza]

Re: This needs a bigger better study

It’s not clear that this an extraordinary claim. It seems that homogeneity of the universe was a bit of an assumption rather than carefully measured, re-measured and peer reviewed fact. At least, not measured to the accuracy possible today.

Given that, there’s no particular intuitive reason to suppose that the universe is homogeneous.

[KittenHuffer]

Re: This needs a bigger better study

Huh? I didn't consider the homogeneous aspect. I saw that they were claiming a different Hubble constant for different areas of the Universe. Doesn't fit with a flat Universe, and there is plenty of evidence of that.

[davenewman]

Since the universe is finite, could it be we are nearer one edge?

[Anonymous Coward]

The universe is not believed to be finite. In particular we believe that is flat (because observations show that it is, to within the accuracy of the observations), which means that, barring some weird global topology, it is spatially infinite, and has always been so, right back to the big bang.

Even if it were finite it would not have edges. A decent mental picture of a finite universe is the surface of a balloon which is being blown up over time: the surface is finite, but has no edges.

[Anonymous Coward]

You don't seem to know what an edge is. You seem to think it has to be sharp.

The edge is the outer limit, thicko.

[Anonymous Coward]

There is no outer limit. There are parts of the universe we can't observe because they're outside our past light cone (and assuming the universe is spatially infinite there is infinitely more of it that we can't see than we can), but there is no physical distinction between those two parts any more than there is a distinction between what I can see through my window and what I can't.

And yes, I do understand this stuff, although I am not current on it any more.

I'm not going to respond to further anonymous comments: in my experience there is almost always a reason for anonymity when pseudo-anonymity is so easy, and it's never a good one.

[Anonymous Coward]

You could say the OP doesn't think edges have to be sharp because he thinks he's edgy, but obviously not the sharpest tool in the box.

[Arthur the cat]

There is no outer limit.

Then what were those old black and white TV programmes I watched? Maybe there was something wrong with my television set after all.

[Version 1.0]

So the Universe is a Klein bottle? Well that explains a lot.

The only certain statement that we can make about the universe is that, while we think we understand the universe, all we have to go on is things that we think exist like the Hubble Constant - what's our best guess for a possible value of that today?

[Anonymous Coward]

AFAIK

From what I can tell of the math, the universe, due to the limit of the light cone/age/photon sphere (edge of observable universe) is "finite" in size. Even the observable universe, would have a limited number of variations of the particle/wave positions and energies within each light cone (14 or so billion light years, adjusted to 30 odd with the expansion rate of the universe).

That's a truly astronomically large number of possible "space" to fill up, and obviously as flat as can be. But still infinitely smaller than infinity. ;)

(What I am saying is that, given any volume of space, the possible number of configurations of matter and energy inside that space is never, ever "infinite", thus given a non infinite size of observational/casual interaction in a universe, it's possible "size" is always non infinite, though given time, will approach infinity as time does. I guess the space could be infinite, but the matter inside it, would necessarily be less than).

[Anonymous Coward]

Re: AFAIK

A lot depends on what we mean by finite.

The number of integers is the smallest infinite number; it was shown (by Cantor) that the number of real numbers is a bigger infinity. Unless we believe that space is actually quantised, space is infinite - because there is always room between any two objects no matter how close they are, and the scale we choose for the universe is arbitrary. On the other hand, if the particle model is correct then the number of particles in the universe can only approach the smallest infinity - ℵ₀ - since particles are in theory countable (even if their number is varying due to interactions, it does so in discrete steps).

If the universe is flat, conceptually it doesn't have boundaries; unlike the surface of the balloon, if we walk far enough we don't return to where we started. It is therefore infinite in extent. If it is quantised in some way, it may be infinite in extent but not in configurations. If it is not quantised, it is infinite (ℵ₁ probably) in spatial configurations, but may only approach ℵ₀ in number of actual particles.

I hope this clarifies the matter, but take leave to doubt it.

[Anonymous Coward]

It says something bad that a comment which describes completely standard current cosmological understanding is getting more downvotes than upvotes, doesn't it? There are a lot of people who live under bridges it turns out.

[Anonymous Coward]

@"It says something bad"

Current cosmological "understanding" doesn't account for these results or this would not be news

[Anonymous Coward]

Re: @"It says something bad"

All our previous cosmological models have been wrong, no doubt the current one is as well: observations like those described in the paper might even be the start of the end for it.

Someone disagreeing is obviously fine: the silent downvote thing is generally not that though, I think. It's one step lower than people who, say, put scare quotes around "model" or "understanding" to try and imply something bad ... oh.

(And the current model being wrong is absurdly unlikely to mean the universe has an edge, whatever that would even mean.)

[Mike 137]

The galaxy has edges though

According to Capt. Kirk the galaxy has edges though, and they're a sort of rippling magenta colour - quite pretty really. So why not the universe? Maybe they're even prettier.

[mr.K]

flat = infinite ?

Okay, this interests me. I have never understood why a flat universe equals an infinite one, or believed to equal at least. I do not see the link. I would really welcome a feedback on this and feel free to correct my assumptions below.

As I understand it, if it is flat the parts that we currently can see can't be all of it, because that would mean that we are in the centre given that we see an equal distance in every direction. Also we do know that it is expanding and stuff should keep falling outside the "visibility edge" (in lack a of a better term), so if it is what we currently see then we have reached a point in time where we see exactly to the edge. Both of which is possible, but so unlikely that it can be disregarded.

However, why can't there be a number between one and infinity? Why can't the universe be one point eleven trillion times bigger than what we can see?

Second question: The surface of a balloon mental picture, isn't that reserved for a curved universe?

[Anonymous Coward]

Re: flat = infinite ?

[Caveat: as I said elsewhere I'm not current in this – the last time I was people had no idea if the universe was flat or not. People who are current should correct me!]

You are correct that flatness on its own does not imply infinite (where by 'infinite' I technically mean 'infinite or topologically odd': for instance the universe could be topologically a torus, which can be flat, but we assume it is not like that). However there are some strong reasons to believe that flatness does imply infinite.

First of all, flatness and the cosmological principle really do imply infinite. One way of phrasing the cosmological principle is that we're not in some special place in the universe (we may be at a special time: what's called the perfect cosmological principle would say that we're not, but we don't think that's true). What that means is that, for everyone, the universe should look about the same, and that means that it seems to be flat for everyone, everywhere, which can't be true if it is finite.

So, well, the cosmological principle is just a principle, and although it seems extremely compelling it could be wrong. So if we assume it is flat, but the cosmological principle is wrong, then here is some kind of 'edge'. And then there's a question about what that edge would be like, which is a whole other thing which I think is problematic. But we can avoid thinking about that, because, if we believe that the universe is expanding, then, if it's finite, then once it was a lot smaller. And in fact, once upon a time it was as small as we like. Now I have to think hard about the geometry but I am almost sure that this means that, whatever we mean by the 'edge', if we look back far enough then it appears in our past light cone: we can see it, in principle. But we don't see it: the CMB is extremely isotropic for instance. Well, perhaps it's so far before the time where the CMB originated that not only is it not visible to us but that whatever trace it left has got lost.

Well, that could be, but this is all looking like special pleading: in order for this idea to work we have to make a whole series of assumptions which, if we just did not make them, would make things hugely simpler and explain what we observe just as well. So, well, let's drop those assumptions and assume it's infinite, which is the simplest case.

(You can ignore the following two paragraphs: I got sidetracked.)

So the other option is that the cosmological principle is true, but the universe is not, quite, flat: it has very small, positive curvature. There's a parameter, Ω, which describes the curvature of the universe, and if it's flat, then Ω = 1. But, if we're right about the universe expanding, then one thing that happens is that (1/Ω - 1) (which is 0 if Ω = 1) gets scaled enormously during the expansion. It gets scaled by about a factor of 10^60 since the 'Planck era' (which is very, very close to the big bang). So if Ω is very close to 1 now, it must have been extremely close to 1 in the early universe: in the early universe Ω must have been 1 to within 1/(10^62) or so.

This is known as the 'flatness problem', and there are various answers to it. One is the anthropic principle: we only happen in universes where Ω is close to 1. That's not very satisfactory. The traditional answer is inflation, which can be used to drive Ω to be very close to 1 even if it didn't start that way. A third answer is to say, well, the universe really is flat for some reason we don't know.

(Start reading again here.)

So, I've got a bit side-tracked here: the last two paragraphs aren't actually very relevant. I think the text before that is really the answer: if the universe is flat, but finite, then the cosmological principle is false (which is OK), and we need some kind of model of what the edge would be which we don't have, but even without such a model we would expect to see artifacts of the edge in the early universe, and we don't.

To answer your other question: yes, the expanding-balloon model works for universes with positive curvature. It's just useful to show that an object can both be finite but not have an edge in this case.

And finally note that I've probably said 'we know that ...' &c above. What that really means is that 'if a whole bunch of current theory and observation is correct, then ...'. All of those things could be wrong. We just don't currently think they are (the paper this is all about might, of course, be a hint that they, or some of them, are wrong!).

[Anonymous Coward]

Re: flat = infinite ?

I've realised two things since writing the above: a flat but topologically toroidal universe is not globally isotropic, and I'm not sure that a topologically non-trivial flat universe can be globally isotropic (but I'm not sure about that); and I'm not convinced by my argument about traces of the edges being visible to us in principle.

[Claptrap314]

Re: flat = infinite ?

S1xS1xS1 is a flat isotropic torus.

[Anonymous Coward]

Re: flat = infinite ?

See other reply: I don't think it is, globally: it has preferred directions. So do things like R^nxS^m (certainly R^1xS^1 and I'm pretty sure all of them).

[Claptrap314]

Re: flat = infinite ?

No, really. I majored in algebraic topology. I did my oral on Coxeter groups. S1xS1xS1 is the flat 3-torus. And it is isotropic.

[Anonymous Coward]

Re: flat = infinite ?

OK, can you explain what is wrong with my argument? Remember that this is not just a topological space: it's a Riemannian manifold with a metric. It is certainly received wisdom in GR that Tn (which is I think S1x...S1) is not globally isotropic (see, for instance https://arxiv.org/abs/gr-qc/9605010v2) as a manifold, so if you know otherwise, well, you should say.

[Anonymous Coward]

Was there a big bang?

Not my field.

If big bang is true, the implication is that everything is expanding and moving away from everything else.

Is the background radiation the same in every direction from our observation point?

If not, why not?

Where is our observation point, actually?

I need a recent book, not a text, but written for a 1%er with interest.

[Anonymous Coward]

Re: Was there a big bang?

There are two answers to this.

The first is 'no, it's not, but we would not expect it to be'. The reason we would not expect it to be is because we have no reason to think that the Earth is stationary in the rest-frame of the CMB: it turns out to be moving at around 370km/s relative to it, and this gives what's called a 'dipole' pattern: the CMB appears hotter and brighter on one side and darker and cooler on the other.

Well, that's to be expected: there's no reason to assume that the Earth, is stationary: the Earth is orbiting the Sun which is orbiting in the galaxy and the galaxy itself is presumably moving.

So what we can do is simply use the data about the CMB dipole pattern to compute how fast we're moving and in what direction (this is called our proper motion) and just factor that out.

And this gets us the second answer which is 'very nearly'. The CMB's temperature, once the dipole moment is removed (and you also need to remove a lot of crud from things like the Milky Way, which is full of hot gas) is 2.725K, with a variation of about 0.0005K: about 1 part in 5,500.

Some of this (perhaps all of this) is predicted by existing models: you would expect some variations, some of which may have originated as quantum fluctuations in the very early universe. But there are tempting hints that there may be variations which are not well-explained by existing models.

[Claptrap314]

I'm not at all certain that I agree with this claim. "Flat" does not mean what you might think. I read an article a few years ago that there is a weak harmonic in the CRB which is consistent with what topologists call a "flat torus" (S1 x S1). I'm pretty sure that S3 is still preferred over R3 as the global geometry. All three of these are isotropic.

Note that even if we are in R3, that does not imply that the energy is infinite. If the energy were distributed at a density of e^(-x^2) from some center, it would be finite. Of course, this is anisotropic, but there is no requirement that there be a noticable deviation from flat within, say, 40bly from center.

[Claptrap314]

I mean S1xS1xS1. We are physically 3-dimensional. ;)

[Anonymous Coward]

I'm fairly sure 'flat' means what I think. In particular I talked about 'barring some weird global topology' by which I meant things like a torus.

What I think of as a flat torus (Some rectangular area of R^n with its edges identified suitably) is certainly not globally isotropic (it is locally isotropic): there are geodesics in it which are closed and ones which aren't (I think I can convince myself that there are countably many closed ones, and uncountably many non-closed ones because you can map them onto the rationals & irrationals in the obvious way), and even though it's not quite obvious that there are shortest closed geodesics (because there could be a sequence which doesn't have a limit) there are in fact, and those define privileged directions. Geometrically those geodesics are the ones that are orthogonal to the edges. So such a thing violates the cosmological principle. I'm fairly but not very sure that any similar structure does as well (it's hard to think about things in more than R^2).

Your topologically-R^3 with a globally varying energy density would not be flat from dynamical considerations as you say, and would also violate the cosmological principle of course. I'm not sure if such a thing corresponds to any plausible cosmological solution though: it could well do.

Note that as I've said in some other comments that the cosmological principle doesn't have to be true.

[Claptrap314]

I checked my definitions...

I was thinking "homogenous", which is weaker, as you point out, than isotropic.

Having said that, I have a REALLY hard time with the idea that we can claim to have evidence that the Universe is isotropic as a mathematician would understand the term. So far as I know, due to the limitations of quantum mechanics, we believe that the Universe as the lowest level is a foam, which means that it is trivially NOT isotropic. If you say, "well, sure, but..." you really don't get very far--because the CBR is NOT uniform. This is not a surprise, but it pointedly means that there ARE differences in density in the primordial universe. Moreover, those differences increase with time.

So isotropy in the cosmological sense really is an informal term. Moreover, it is a consequence of the geometry of the universe, which is itself constrained by the physical laws, not the other way around. Given the discussions I read some years ago about the weak harmonic in the CBR, S1xS1xS1 would appear more likely than S3 or R3.

[Anonymous Coward]

Re: I checked my definitions...

Sorry I had not read this before posting my other comment just now. I hope it wasn't rude: it was not meant to be anyway, and I can see we now agree on the global (an)isotropy thing of T3.

So I think there are two things to say here (note: I have a background in this stuff and I did understand some of the maths, but I'm not any kind of academic now so take all this with suitable salt).

One is that we really have no idea about what spacetime looks like at the quantum level because we simply don't have a theory of quantum gravity which works, at all. But yes, some kind of foam or spin network or whatever, and yes, probably not isotropic (whether they can even get these things to be Lorenz-invariant I'm not sure). However, we also know that on larger scales the structure either needs to be well-approximated by the theories we currently believe to describe those scales, or those theories need to be experimentally wrong at the scales they purport to describe. It could be that this is wrong, and that the very small-scale structure shows up on large scales, and that would be very interesting because it would mean we could test QG theories without requiring absurd experiments. In particular a nice thing is this idea that artifacts can show up in the CMB, as you say.

The other is that the whole cosmological principle thing can be wrong (which I think I've said in some other comment here and should have done if I have not). It's pretty much 'let's make the simplest set of assumptions we can – the most symmetry we can have – and see how far it gets us'. And they get us pretty far, because, for instance, the CMB is actually really extremely uniform: 2.725K +- 0.0005K or whatever it is. But obviously not quite uniform! And that itself is a problem of course because we would expect things to get blown up as you say, and yet they don't seem to have been and inflation is meant to be the answer with that and I've never been happy with inflation as it seems like a deus-ex-machina answer to things although I'm sure it's not because people win prizes for it.

So I haven't been trying to argue that the 'cosmological principle must be right and therefore x', but rather 'if the cosmological principle is right then x, so lets look at x and if it turns out to be wrong then so does the cosmological principle'. And yes, all these things should be a consequence of the laws of physics, not the other way around.

I think that globally S3 or R3 seems much more likely to me than T3, but (a) my opinion is worth nothing and (b) this is something we should go out and look for obviously.

[Chris G]

Dark energy

Since we can't detect it directly, or touch it, feel it ,or measure it. I was wondering I f I could blame it the next time I get caught speeding.

":I was dring along minding me own business yer honour when suddenly my car went faster sndvfaster of it's own accord, I think I passed through a band of Dark Energy".

Think I'd get away with It?

[Anonymous Coward]

Re: Dark energy

Hopefully not. Slow down, you murderous P. O. S

[mr.K]

Re: Dark energy

Nah, you should try to change the point of reference.

"Yes, I was driving 85 mph in reference to this state, but I believe this is an interstate highway and thus I should use Washington DC as a reference frame. So according to this bit of trigonometry and factoring in that DC also is further north thus moving slower and I was moving against the rotation of the earth, I would like to point out that..."

[John Brown (no body)]

Re: Dark energy

Is Dark Matter/Energy the new Aether?

Archeologists usually use "ritual purposes" when they don't know.

As for the expansion difference, is it not just that our universal bubble has just bumped up against another universal bubble in the multversal foam?

[Anonymous Coward]

Re: Dark energy

Ahh, I see you have taken recourse to the protective ward against downvotes. And is that a clove of garlic behind the incantation? Double the protection!

[Anonymous Coward]

Re: Dark energy

Is Dark Matter/Energy the new Aether?

No, they're more like the anti-aether: aether was something people expected to be there but then turned out not to be. Dark matter & energy are something people didn't expect to be there, but there turns out to be increasingly compelling evidence that they are there.

For a classical GR person like me, dark matter is the interesting one: in terms of classical GR dark energy looks just like a non-zero cosmological constant and then the question, really, is why did we assume so strongly that it must be zero for all those years when there's no reason at all do do that, since it's just a constant of integration really? (Of course, people who want to predict dark energy based on vacuum energy find it a whole lot more interesting.) Dark matter, on the other hand is much more interesting because it's not just some parameter of the theory we got wrong, and in particular the nice other possibility – that 'dark matter' just tells us that GR is wrong – seems increasingly unlikely to be the case.

[MarkET]

Quantum Mechanics?

Does not the entropy of a quantum system alter with observation?

"If the isotropy hypothesis was correct, the properties of the clusters would be uniform across the sky. But we actually saw significant differences."

[Grikath]

Re: Quantum Mechanics?

Ummm... This is stuff at the macro scale. Very much macro.

So definitely not a quantum effect, whichever way you look at it.

[Anonymous Coward]

Re: Quantum Mechanics?

A neutron star is pretty macro but what goes on in it is strictly quantum.

[Anonymous Coward]

Re: Quantum Mechanics?

What goes on in any object at all is strictly quantum: you can't explain, really, anything without quantum mechanics. You need QM to understand how the matter of which they are formed works, in both cases. You need to understand the various forces which work, in both cases: you only need electromagnetism for the chemical structure of the apple, but if you want to understand the nuclei of its atoms you need the strong (& probably weak?) forces; you don't need (classical, not quantum) gravity to understand the structure of apples, but you do need it to understand the structure of neutron stars.

So if you want to understand the properties of the matter of which these objects are made, you need QM. Some of those properties, in the case of neutron stars, may be odd to us (superfluidity in their cores for instance).

But none of this means you need to start worrying whether, say, apples, or neutron stars have some weird global quantum properties: they're too big and too hot.

[Anonymous Coward]

Dark energy & the cosmological constant

If these findings are correct (which, sadly, they probably are not I suspect) then they could have very profound consequences. I think we know that the CMB is isotropic to very good accuracy & hence the universe was isotropic at the time that the CMB light started out. If it's not isotropic now then something drove that, and the thing that has become dominant in the dynamics of the recent universe is dark energy. If dark energy is the cosmological constant of GR then it would not drive anisotropy, so it can't be that, if the observation is correct. That would be very interesting, I think.

(They at least allude to this in the paper but I have not read all of it.)

[Arthur the cat]

Here's a bug report for cosmology

I've tried filing bug reports for the universe, but all I get back is

WILLNOTFIX - remember which one of us is omnipotent, you ungrateful oik!

[Androgynous Cupboard]

Re: Here's a bug report for cosmology

Better than "it's an open universe, you can always fork it and fix it yourself"

As an aside, I can't get past the notion that trying to divine the shape of the universe from earth is like trying to work out the shape of Albert Hall by peering through the keyhole.

[vtcodger]

Re: Here's a bug report for cosmology

Better than "it's an open universe, you can always fork it and fix it yourself"

Not a bad idea ... But the documentation seems to be sadly deficient.

[Anonymous Coward]

Re: Here's a bug report for cosmology

Typical Open Source project.

[Anonymous Coward]

Re: Here's a bug report for cosmology

You need to submit your bug reports in old Enochian if you want them to be listened to. But you probably do not want them to be listened to given who, or what, might be listening. You definitely do not want That Which Fixes Bugs to start paying attention to your bugs, still less fixing them. T̴̴͡r̴̨u̷̴st̴͠҉ m͟͢͝e͘͟ ̷͡͠o͡ņ͘ ͟͢͡t͠his̶͢.̛̀

(Now, seriously, why is there no 'Great Old One' Icon? What were they thinking about?)

[Arthur the cat]

Re: Here's a bug report for cosmology

Upvoted for the Strossian reference.

[Paul Shirley]

Strangely matches other observations

The range of Hubble values in that map is similar to the range of values different groups using different measurement methods are still coming up with for the constant.

Maybe a clue that there really isn't a single correct value and our patch isn't quite as flat as believed.

[Denarius]

state of play

There appear to be slight evidence of concentric shells of galaxies and galactic clusters, with 2000 million light year spacing. Yes this challenges the isotropic concept. So more data analysis from whatever sky survey is relevant. Given the fudges to make Big Bang theory appear workable perhaps it is time for a new model. And no, I have no idea of what that might be. It is just a model where most of what is claimed to exist, but cant be seen or directly measured seems a kludge.

[Doctor Evil]

constant?

"The Hubble constant, an indicator of the rate of expansion, is lower for the observed galaxies on the right side of this diagram compared to the left."

Wouldn't that make it more of a Hubble variable, then? Not really constant, is it?

[Claptrap314]

Re: constant?

Back in the '90s, I used to annoy physicists by referring to the "Hubble variable"--where variable in this sense actually referred to our changes in what we thought the Hubble constant is. Maybe I was more correct than I anticipated...

[Anonymous Coward]

That's just the CMB anisotropy dipole due to the solar system moving with reference to the rest of the universe.

[Anonymous Coward]

I really hope they corrected for that: they're goong to be embarrassed otherwise!

[Stoneshop]

when viewed across large enough scales.

Do they have a duck on one side, and a purported witch on the other?

[Tictactaylor]

It seems similar to doppler effect. Maybe the bending of time like a sound wave is a basic interpretation.

[Tictactaylor]

It looks similar to doppler shift. We may not be one universe, but many layered over each other, parallel universes, but visible simultaneously similar to how individual frames make up a movie. Each frame being a considerable time period though.

[briesmith]

I'm sorry, excuse me

I think those other universes should just get out of our way. We're the humans and our universe is the best. They should know their place.