As in, how does the universe expand, through another spatial dimension, etc?
see my blog and the references.
It's true that the universe is 'apparently' expanding faster than the speed of light, right?
the accepted theory uses post-1850 geometry and this allows expansion without anyone needing to fantasize another spatial dimension. the systematic increase in distances just happens internally (no exterior needed)
the word apparently indicates that you may be misunderstanding what is being talked about. Faster than light expansion is real.
Note that expansion refers to the systematic increase of distances according to Hubble Law which in brief says that largescale distances are increasing at present by about 1/140 of a percent every million years.
it is based on empirical observation. if you work it out, it means that any distance which at this moment is bigger than 14 billion lightyears is, at this moment, increasing faster than c.
since most of the objects in the observable universe are farther away than 14 billion lightyears, MOST distances to things are increasing faster than light speed.
Expansion of distance is real, it is routine and, in some sense, it is required by Einstein relativity. General Relativity is essentially the only theory of gravity we have that works precisely and has passed all the observational tests---it is also our only theory of spacetime geometry. That is GR is our only theory of how distance behaves. If you derive a model of the universe based on GR and fit it to the data then you see that distances HAVE to be expanding in the way Hubble Law says they are observed to expand.
If we didn't see distances increasing faster than light, that would in effect violate General Relativity (as specialized to fit the data) and would be terrible news. The bottom line is: faster than light increase in most distances is both what we EXPECT based on the accepted theory of gravity, and also what is consistent with observational data.
So take out the word apparently and ask the question again
The answer is you got it right! Yes! In the sense of spatial distances increasing faster than light.
It is a bit vague to say the universe is expanding. You should focus on spatial distances. there is no Hubble Law expansion of time! the expansion is not about the whole 4D spacetime history of the universe. so people say the universe is expanding just as a quick vague shorthand when what they mean is the on-average increase in very largescale spatial distances
It is really a sloppy thing to say the universe is expanding because it gives the impression that the universe has a known SIZE and that this size is increasing. that is not strictly true. We don't know the size of the universe. It might even be spatial infinite. Or spatial finite but much larger than what we see.
It would be better to every now and then make clear that what you really mean is that the present distances to remote galaxies are increasing by a certain small percentage every year. (so naturally the longer ones are increasing faster)
If both an expanding universe and SR are correct, couldn't we use length contraction to explain the expansion? Say the universe is continuously expanding at an apparent length, L', but if the universe is expanding at a velocity greater than c, then the length of the universe in its rest frame is imaginary, or undefined, which then suggests....?
In the distances getting further apart faster than the speed of light theory, is Lambda (dark energy) expanding faster than light, if it is and Lambda is treated as normal energy/mass, has gravity, would that not be a problem?
cosmology is based on GR, and GR uses SR as a local approximation that fits an immediate neighborhood. But in GR we generally acknowledge that SR does not apply the whole schmeer. It applies locally but not globally.
So there is no reason to assume that SR is correct on a global scale. It's destiny is to be used as the basis for a huge number of local coordinate systems, like the maps in an Atlas.
No one flat map fits the whole thing. But separate individual flat maps, like the map of your city or state, fit pretty well.
That was the essential thing about Riemann's 1850 break-through. The idea of an Atlas of local maps, local frames, local coordinate patches. For him the local patches were Euclidean, and what was patched together could be wildly non-Euclidean, but the idea is there: local maps.
Einstein used SR for the local coordinate patches, and the GR thing patched together could be wildly NON-SR. It could totally disobey special relativity.
So your problem is with your premise---globally speaking, why assume that SR is correct?
The other things you say in your post seem to evoke the idea that the universe is in a moving frame? Or we are moving relative to it???
That is not how cosmologists normally view it. We usually study the universe from the standpoint of a universal rest frame. The observer is not moving relative to the Cosmic Microwave Background.
If the observer were moving relative CMB then there would be a doppler hotspot ahead of him and a doppler cold spot behind. But we look at the universe from a non-moving standpoint. And the distances are increasing at the same rates in all directions---not slower in one direction and faster in another.
So the UNIVERSE AS A WHOLE IS STATIONARY from our point of view, and we are stationary with respect to it. that is after some corrections have been made for the sun's motion in the galaxy and the galaxy's motion in the CMB.
SO THERE IS NO LENGTH CONTRACTION from the universe being in a moving frame.
and in fact what velocity would you propose to calculate a length contraction with?
the recession speeds of distant galaxies are all different---the rate of increase of the distance is proportional to the distance---long distances increase at a faster rate.
so there is no one speed that one can say the universe is expanding at this speed.
and even if there were, expanding is not moving.
in fact, as we study it in cosmology, the universe as a whole is not moving and there is no Special Rel effect.
I was simply saying that anything traveling faster than the speed of light, be it 2c or 3c, calls for an imaginary contraction/dilation.
I don't really understand this. The universe is making more space, and as it expands, our size in comparison to other masses stay the same, while our size in comparison to the universe gets smaller. How can it be stationary under these terms?
I meant stationary in the sense of not moving relative to us. Growing of course but it's not as if it has a center of mass that is going right or left or north at 37 miles per hour.
When we are stationary with respect to the CMB we are at rest with respect to the universe and it is at rest with respect to us.
It is still growing of course. I didn't mean static. distances are increasing at a great rate.
sorry if I didnt make it clear, epkid. Maybe we have different notions of what it means to be stationary.
Here is something to get your mind around: maybe the most important thing we observe in astronomy is the CMB. light that was emitted from thin hot gas at about 3000 kelvin, same temp as the surface of some stars----as the gas was cooling down just enough to stop being ionized and become transparent
that light was emitted from gas that was 40 million LY away from the material that eventually formed us, and that matter was receding from our matter at about 57 times c
(at the time the light was emitted)
the light has been traveling for about 13.6 billion years, during which time distances have expanded by a factor of 1100, and the wavelength of the light has become longer by a factor of 1100. and we are now receiving the light.
the matter that emitted it is now some 46 billion LY away from us
all the while the light was traveling, it was going at a speed of c in terms of the local coordinates of whereever it was. cause that's how fast light travels
so it started out coming towards us when it was only 40 million LY away from us
but it took 13.6 billion years to get here
and when it arrived its wavelengths are longer by a factor of 1100
(that's the factor by which distances increased during the 13.6 billion years the light was in transit, and it's what is called the redshift---actually z+1, the redshift plus one is the expansion factor.)
You asked about what is the accepted theory in expansion cosmology. I am giving you a concrete example of what the accepted story is, in this case, with some approximately right numbers. the accepted theory is built into the online cosmology calculators like the one at Ned Wright's website
and the Morgan calculator in my sig. You should play around with standard model cosmology calculators and get used to the numbers. assimilate the numbers.
to use Morgan's, put 0.27 in for the matter fraction, put 0.73 in for Lambda (the dark energy fraction), put 71 in for the Hubble constant and then you are ready to go.
Put in 1100 for the redshift and see what you get.
or put in some other redshift, like 7. lately people have been finding galaxies with redshift 7 and up.
Here is the url for Morgan's calculator that I keep in my sig
Here's Ned Wright's calculator
Here's Ned Wright's cosmology tutorial website
I'd suggest you get some hands-on experience with the standard cosmology model
Forget about special relativity for a while (its speed limit doesn't apply to expansion) and get used to cosmology
Good luck! Hope this advice helps.
I think what you're saying is that at any point in time, there isn't a center, suggesting a balloon analogy, but my question is, given it's like balloon, how does it expand through another spacial dimension? Why can't we travel through that dimension etc? Isn't that what a balloon model suggests?
Hi Wolram, I don't understand what problem you see. Maybe you can say on what basis there's a problem.
People keep trying to apply the Special Rel speed limit! It simply doesn't apply to recession speeds. Recession speed is different from relative motion in SR. Recession speed is the Hubble Law rate of increase in large distances---it is not relative motion in a local frame.
What SR speed limit says in a nutshell is that nothing can catch up with and pass a photon. Absolutely true!
But galaxy can be receding from us at 3 times the speed of light and it still will not be able to catch up with a photon. Because the photons will be receding even faster.
So Special Rel is kind of harmless, in the context of recession speeds. The SR speed limit doesn't concern us.
You bring up dark energy. The space around the galaxy contains dark energy. We can consider that too. As having a mass equivalent. So both the dark energy and the galaxy are receding from us at 3 times the speed of light. Since the Special Rel speed limit is not being violated, either by the dark energy or the galaxy, just as in the previous case it doesnt concern us.
Nobody is catching up with and passing a photon, not the galaxy, and not the dark energy.
So bringing up dark energy doesn't really change things as far as I can see.
G'dya from the land of ozzzzzzzzzzz
Its seems so logical the Big Bang Theory and the expansion and faster than the speed of light.
But! Something is missing.
Scientific evidence. If you can test it once and is able to be repeated time and time again.
Take any evidence and try to prove it.
Better still, by observations.
There is an abundance of precise direct and indirect observational evidence for both the BBN theory and superluminal recession of matter at large spatial distances. Is this what you meant? Check out Ned Wright's Guide http://www.astro.ucla.edu/~wright/cosmolog.htm" [Broken] and do a little reading, I assure you the evidence for each phenomenon is clear! Marcus could probably provide more direct links if you ask nicely...
G'day from the land of ozzzzzz
I do quite a bit of reading and I have read
Welcome to Ned Wright's Cosmology Tutorial
I do not take it as evidence,
I have not seen one observation that shows that super clusters are moving away from each other.
Not only that, no scientific explanation has been given to explain the formation of more than a 100 billion galaxies forming in just 500 million years. Not only that, their formation at the same time. Yes you can use ad hoc ideas to make it work, but! thats not the answer that I want.
We cannot go to these super clusters to see things from their point of view, neither can we run tape measures to see if mutual distances between them are increasing, however under the Copernican principle, and given that further clusters do exhibit a greater red shift than nearer ones, (where the further galaxies subtend smaller angles), then it is as reasonable a conclusion that they are moving away from each other, as is the conclusion that local galaxies are moving away from the Milky Way.
The increasing red shift with distance of the light from these super clusters is the observation you are looking for.
G'day from the land of ozzzzzz
Local galaxies are not moving away from the Milky Way. If you have evidence to support that, I'm all ears. As for redshift of the super clusters of galaxies, I would like to see the links that give the evidence that the super clusters are moving away. The Big Bang theory states that the Bangs occured evenly throughout at the same time. The complication that we have is the recycling process that we can observe through black hole jet formation and ejection of matter reforming the galaxies.
You hit the nail on the head. If I took someones word for it, I would not do justice for science. The evidence that I'm looking for will not be available for another maybe 4 yrs.
Yes I have read links day in day out, I understand the problems with redshift and the ability for objects to produce the redshift without moving away, particularly super clusters.
Please do not think that I'm a trouble maker. This has been on my mind for the last 40 years.
After reading these links and many others, I think redshift data is in question:
Separate names with a comma.