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Author Topic: What is the evidence that the Universe is expanding?  (Read 12768 times)

Offline barneyboy

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Apart from the red shift, what other evidence is there for saying the universe is expanding at an ever increasing rate please as you could get the red shift from a shrinking universe as well. please keep the answers fairly simplistic as im no prof ;D
« Last Edit: 11/11/2013 19:20:12 by chris »


 

Offline Pmb

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Re: proof for the expantion of the universe.
« Reply #1 on: 03/11/2013 22:56:07 »
Apart from the red shift, what other evidence is there for saying the universe is expanding at an ever increasing rate please as you could get the red shift from a shrinking universe as well. please keep the answers fairly simplistic as im no prof ;D
The only evidence that the universe is expanding comes from cosmological redshift
 

Offline evan_au

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Re: proof for the expantion of the universe.
« Reply #2 on: 04/11/2013 08:13:58 »
A century before Hubble, Olbers' Paradox* was an early indicator that something was wrong with a steady-state model of the universe. The most widely-accepted explanation of this paradox also refers to redshift.

*Why doesn't the sky glow with a uniform intensity of the surface of the Sun?
« Last Edit: 04/11/2013 09:00:20 by evan_au »
 

Offline evan_au

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Re: proof for the expantion of the universe.
« Reply #3 on: 04/11/2013 09:05:21 »
In formulating his theory of relativity, Einstein realised that the steady-state universe was not a stable solution to his equations.

The universe could be contracting, or expanding. Without a carefully tuned cosmological constant, a steady-state universe would be at best a passing phase in the life of the universe.
 

Offline woolyhead

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Re: proof for the expantion of the universe.
« Reply #4 on: 09/11/2013 13:44:16 »
Apart from the red shift, what other evidence is there for saying the universe is expanding at an ever increasing rate please as you could get the red shift from a shrinking universe as well. please keep the answers fairly simplistic as im no prof ;D
A shrinking universe would produce an increase in the frequency whereas the change observed is a decrease, showing that whatever is looked at is moving away from us. This happens in very direction where we look.
 

Offline Pmb

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Re: proof for the expantion of the universe.
« Reply #5 on: 10/11/2013 12:42:29 »
Apart from the red shift, what other evidence is there for saying the universe is expanding at an ever increasing rate please as you could get the red shift from a shrinking universe as well. please keep the answers fairly simplistic as im no prof ;D
A shrinking universe would produce an increase in the frequency whereas the change observed is a decrease, showing that whatever is looked at is moving away from us. This happens in very direction where we look.
There is a difference in the fact that things moving away are redshifted and things moving toward us are blue shifted. Doppler shift is a different phenomena than cosmological redshift. The former means that objects emitting light are moving away from us where as the later means that the distance between us and the object moving away from use is increasing because the size of the universe is increasing.
 

Offline Ethos_

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Re: proof for the expantion of the universe.
« Reply #6 on: 10/11/2013 15:40:52 »
The former means that objects emitting light are moving away from us where as the later means that the distance between us and the object moving away from use is increasing because the size of the universe is increasing.
If I understand you correctly then, you are saying that the Metric, "space-time fabric" is expanding and the expansion is not only the result of changing distance between material objects within the universe???
« Last Edit: 10/11/2013 15:43:28 by Ethos_ »
 

Offline Pmb

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Re: proof for the expantion of the universe.
« Reply #7 on: 10/11/2013 20:02:17 »
The former means that objects emitting light are moving away from us where as the later means that the distance between us and the object moving away from use is increasing because the size of the universe is increasing.
If I understand you correctly then, you are saying that the Metric, "space-time fabric" is expanding and the expansion is not only the result of changing distance between material objects within the universe???
Yes. To be more precise - The distance between galaxies is increasing because space is being created between them continuosly.
 

Offline Bill S

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Re: proof for the expantion of the universe.
« Reply #8 on: 10/11/2013 21:57:23 »
Quote from: Pmb
The distance between galaxies is increasing because space is being created between them continuously.

Is space (spacetime?) being created or is it "stretching"?

Is there a difference?

If so, how would we know which was happening?
 

Offline Ethos_

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Re: proof for the expantion of the universe.
« Reply #9 on: 10/11/2013 22:12:46 »
Quote from: Pmb
The distance between galaxies is increasing because space is being created between them continuously.

Is space (spacetime?) being created or is it "stretching"?

Is there a difference?

If so, how would we know which was happening?
Good question Bill. I'm not sure we can know at this juncture with our present technology. The difference between "stretching and the creation of new space" may be difficult to define anyway. What do we mean when we speculate that space-time has been stretched? Is there really any difference between that notion and the creation of new space? Very curious indeed!

« Last Edit: 10/11/2013 22:20:15 by Ethos_ »
 

Offline Ethos_

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Re: proof for the expantion of the universe.
« Reply #10 on: 10/11/2013 23:47:03 »
After thinking a bit about your question Bill, it appears there may be a difference after all.

Adding new space would probably not effect material objects present before the addition of the new space. However, if we consider the consequences of stretching the Metric, we discover a flaw with that reasoning. This is true because; If every dimension is strecthed, and BTW,  that would include the space within all  particles too, every dimension would appear to remain the same to us, the observer. We would never see any change. Because we do observe the expansion, it would be safe to say that it is only an addition of new space-time that is occurring.
« Last Edit: 11/11/2013 00:12:14 by Ethos_ »
 

Offline Pmb

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Re: proof for the expantion of the universe.
« Reply #11 on: 11/11/2013 04:05:53 »
Quote from: Bill S
Is space (spacetime?) being created or is it "stretching"?
My first reaction is to why bother asking since it seems nothing more to me than mere semantics. In the end we must be able to perform an experiment to determine which is which and from what I’ve gathered so far this won’t get us anywhere.

What is important is what it all means in the end. The universe is said to expanding because there is more and more room being created. In essence all that really means is that we have more places to put things. Nothing else.

Quote from: Bill S
Is there a difference?
No. It’s useful to think in terms of analogies such as the balloon one which is of the surface area of an expanding sphere. Just make sure you don’t take that old adage of “the fabric of spacetime” and think it’s some sort of “fabric” that’s being manipulated. Just like the cheese between my toes. :)
 

Offline Pmb

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Re: proof for the expantion of the universe.
« Reply #12 on: 11/11/2013 07:14:50 »
I came up with a simple model which will illustrates the ideas behind an expanding universe and the idea that space is being created. I call this model The Circle Universe and it has a radius R which parameterizes the size of the Circle Universe. Let theta represent the relative angular displacement of two “observers” on the circumference” of the Circle Universe. The metric which determines the distance between two such points is L = g(theta) = R*theta. If the two observers remain at rest then the rate change of the distance between them is dL/dt = (dR/dt)*theta.

Notice that when R = 0 then size of the universe was also zero and all points were at the same point. Also there is no point in the Circle Universe that can be said to be at rest. Does this mean that there is space being created/is expanding in my model of a Circle Universe or does it mean that the distance between the two observers is being stretched? Notice that it really doesn't matter which is the most correct. It only matters that we know how to describe it to others.
 

Offline barneyboy

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Re: proof for the expantion of the universe.
« Reply #13 on: 11/11/2013 19:39:06 »
thanks for the replies, but if the universe was shrinking surely you could also have redshift in all directions, stretching/more space being created and an increase in the speed that galaxy's moving apart. When matter is pulled towards an event horizon it speeds up in a similar way fluid speeds up the closer to a plug hole it gets. As it does, it stretches away from the surrounding matter as its accelerates so from the view point on any piece of matter all other matter is moving away as space stretches.
so if the universe is collapsing from the centre outwards (like a collapsing star) you would not need to use dark matter to explain the speeding up/expanding universe. ???
 

Offline Pmb

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Re: What is the evidence that the Universe is expanding?
« Reply #14 on: 11/11/2013 21:26:00 »
Quote from: barneyboy
thanks for the replies, but if the universe was shrinking surely you could also have redshift in all directions, stretching/more space being created and an increase in the speed that galaxy's moving apart.
I don't understand where this is comming from. Are you now changing the subject totally around to be something entirely else?

"surely"? Why "surely"? A shrinking universe would be a contracting universe and the result would be a cosmological blue shift, not a cosmological redshift. What's leading you to believe that it would still be a redshift?

Quote from: barneyboy
When matter is pulled towards an event horizon it speeds up in a similar way fluid speeds up the closer to a plug hole it gets.
But there's no event horizon here and no cosmological contractions/expasions in that case. Where did you all of a sudden bring up event horizon's?
 

Offline spartaman64

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Re: What is the evidence that the Universe is expanding?
« Reply #15 on: 15/11/2013 03:06:19 »
The red shift from other galaxies show that other galaxies are moving away from us so the universe is expanding.
 

Offline barneyboy

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Re: What is the evidence that the Universe is expanding?
« Reply #16 on: 15/11/2013 23:16:40 »
I asked the original question like I did first to see if there was any other indicator that the universe was expanding other than just the red shift. I apologise if this has annoyed anyone but I know that I would be shot down if I just said "how do you know that the universe is shrinking". so :
 If the universes was contracting from its outer regions back to the centre point then there would be a blue shift as galaxy's would be "squashing" back together but if the universe was collapsing from the centre outwards the distance's would increase as the nearer to the centre they were, the faster they would go, as I said, like water getting pulled towards the plughole or like matter falling into a singularity.
if you don't like my analogies im sorry but its the simplest way I could think of to ask my question
 

Offline barneyboy

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Re: What is the evidence that the Universe is expanding?
« Reply #17 on: 16/11/2013 00:27:06 »
Sorry pmb I though my first reply was clearer than it was, I was using the event horizon analogy just to show that things can shrink to a central point yet accelerate away from us and stretch the space between two points yet still be collapsing.
 

Offline yor_on

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Re: What is the evidence that the Universe is expanding?
« Reply #18 on: 17/11/2013 12:23:04 »
Nice thought. Are you imagining a universe in where everything (of matter?) sort of are becoming 'black holes', although as you include the 'space' around it possibly make it keep a equilibrium? Then you will need a lot more dimensions for it, I think? Or you can possibly use (non-classical) 'locality' to define it. Alternatively described it's the idea in where everything are shrinking in a fixed 'volume' of a container-universe, giving us a redshift. If the universe can be defined as a 'container' then the last is as possible as one in where that 'container' is expanding producing a redshift. From my point of view (non classical 'locality') 'c' is communication, and although a shared 'constant', theoretically observer dependent. To see that one just think of how light always will be measured at 'c', doesn't matter how or on what you measure, as long as we're not discussing accelerations/decelerations. That's what makes it a 'constant', and to my eyes, observer dependent. And from such a view distances becomes a very fluid definition, as well as speeds.
=

Observer dependent relative the idea of a 'commonly shared universe' that is. Doesn't mean I envision a 'universal container' filled with 'time dilations and Lorentz contractions'. Such a universe that I'm considering here is just a way of communicating, defined through commonly shared principles and constants (always locally defined). The 'container' we see is of our own making, defined through those local experiments.
« Last Edit: 17/11/2013 12:32:33 by yor_on »
 

Offline barneyboy

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Re: What is the evidence that the Universe is expanding?
« Reply #19 on: 18/11/2013 21:42:09 »
Thanks for that, Yor-on, but rather than all matter becoming singularity's, I meant that if the universe came from a single point and "the big bang" event was able to fling out all the material that makes up this universe, why not have a big crunch.
I know that this theory has been looked at already but under the premise that the matter at the furthest most reaches of the universe will start to collapse inwards.
My thought is that at the same point that the big bang occurred so to could the big crunch, a point in space that is pulling all matter back to its origin therefor stretching space back towards its origin, keeping the redshift intact. Like you said, all matter from a single container but now the container is pulling it all back.
 The outer edges of the universe could be still expanding or even stationary as long as every thing else is moving back towards the original start point, the nearer to the original start point the faster they go, distances increase even as the universe decreases.
At the point that the universe came into being the laws of physics as we know it did not apply did they? The matter thrown out exceeded the speed of light, vast quantity's of material appeared and exotic forces came into being, even if it was only fleetingly, all impossible in our understanding of physics so maybe at that point in space/time where it all started, physics still do no apply, as they do not in a singularity, and all matter is being pulled back to its original state, at its original point.

please see my other post for my explanation why I do not ask questions in the manor that you are probably accustomed to  :I
 

Offline yor_on

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Re: What is the evidence that the Universe is expanding?
« Reply #20 on: 18/11/2013 22:04:00 »
hmm :)

Are you suggesting a shrinking container, with a even faster shrinking matter content? Or that the matter content stops shrinking at some time while the container itself keeps on shrinking?

The first case will produce a red shift, but it can't become a 'big crunch, as the container always must be bigger than its matter content to keep a redshift.

The second should mean a blueshift.
 

Offline barneyboy

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Re: What is the evidence that the Universe is expanding?
« Reply #21 on: 18/11/2013 22:14:19 »
I was actually meaning that the container is a fixed point, the original container that held all matter infinitely small and that all matter that has escaped is now being pulled back into it, increasing in speed as it approaches (and if ive got this right, the closer to the speed of light matter travels at the smaller it becomes) cramming its self back into the container that it originated from.
the increase in speed the closer to the container matter got would continue to stretch space the closer it got and this would account for the red shift  :o)
 

Offline Pmb

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Re: What is the evidence that the Universe is expanding?
« Reply #22 on: 18/11/2013 23:14:28 »
Quote from: barneyboy
Thanks for that, Yor-on, but rather than all matter becoming singularity's, I meant that if the universe came from a single point and "the big bang" event was able to fling out all the material that makes up this universe, why not have a big crunch.
The universe coming out of a single point is not part of the big bang theory (BBT). The BBT can only traced back so far and then we don’t know what happened before that.

Physicists used to believe that the universe might stop expanding and reverse to a big crunch. That was only one of the possibilities. Now that it appears  that the universe is expanding at an accelerating rate that does not seem possible.
[/quote]

Quote from: barneyboy
I know that this theory has been looked at already but under the premise that the matter at the furthest most reaches of the universe will start to collapse inwards.
The matter everywhere is expanding or collapsing at the same time regardless of how far away it is.

Quote from: barneyboy
My thought is that at the same point that the big bang occurred so to could the big crunch, a point in space that is pulling all matter back to its origin therefor stretching space back towards its origin, keeping the redshift intact.
There is no place in the universe like that. People get the wrong idea quite often that the big bang occured at a particle point in spacel which is not true.
« Last Edit: 18/11/2013 23:17:02 by Pmb »
 

Offline yor_on

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Re: What is the evidence that the Universe is expanding?
« Reply #23 on: 19/11/2013 12:20:11 »
Barney, I lose you there. Either you define the universe as a container, containing it all, matter, light and energy and .... Or you define a universe as a result of local experiments, sharing common principles and constants. To do both simultaneously becomes a very tricky proposition as you now on one hand define a 'empty container (universe)' with what, outside it? Another container containing those stars etc 'rushing back' into this original container?

Why would they need to do that?
=

Are you considering some 'center'? That somehow 'calls back' all matter? Then that's not a 'container' as I'm thinking of it. A 'container' is to me just a universe, and all it contains. And there is no center to it, using the model we have today. The universe expands equivalently from all fixed positions, aka planets, you measure that expansion from. And that is also a very strong argument for this 'container' to be considered 'infinite'. As it otherwise should be so that at some position xyz and time you would find a 'uneven expansion', if the universe has borders. That doesn't necessarily mean that the universe can't be 'contained' as described from some 'outside', only that it to us inside is 'infinite' and 'seamless'.
=

What such a reasoning does is bringing us back to what a 'infinity' consist of? Using a 'one to one correspondence' to define it, can a infinity expand? Isn't all infinites the same? Or put in another manner. If the universe has a 'outside', being a 'container' of us/it all measurable. Is that a 'real' infinity, using a one to one correspondence?
=

(A 'one to one correspondence' is you putting one thing beside another, ad infinitum, comparing them (their position) with each other. If you have no end to that, you should have yourself a infinity... As taking all primes, placing them aside all natural numbers... In a 'system' limited by your defined 'borders, cut offs' there will be less primes than natural numbers, but as both, each by itself, seem to be able to be counted up 'ad infinitum', you should be unable to end a 'one to one correspondence' placing numbers aside each other. In reality making them equivalently 'infinite', if you see how I mean.)
« Last Edit: 19/11/2013 13:08:01 by yor_on »
 

Offline barneyboy

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Re: What is the evidence that the Universe is expanding?
« Reply #24 on: 19/11/2013 21:51:45 »
Yes I did mean a sort of centre, the original expansion point and I see what you mean about my container usage, sorry  :I
what I meant was that at the moment of the big bang, all matter in the universe today was released (all be it in a different form). for a very small period of time, there was an unimaginable force that flung all the matter outwards. it flung it so hard that it expanded outwards faster than light (impossible within our {yours more than mine :o)} understanding of physics) until matter slowed and the laws of physics came into play.
so expansion started fast then slowed and now is speeding up again?
whats to say that that unimaginable force is not now drawing all matter back.

Please bare with me on this next bit.
one theory of the big bang, so ive read, is that two "wavy branes" of a multiverse touched and at the point that they touched our universe was created. two ultra massive bodys with masses of energy released matter and energy in an instant to create our universe. now the branes are pulling apart again and their drawing their energys and matter back out at the point that they first touched.
an unimaginable force inflating then deflating our universe.
now whether its two wavy branes separating, an uber super massive black hole or just GOD with a big vacuum cleaner whats to say that the generally accepted unimaginable force that blew us apart isn't now drawing us back in, ever faster the closer to original start point you get.
« Last Edit: 19/11/2013 22:01:26 by barneyboy »
 

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Re: What is the evidence that the Universe is expanding?
« Reply #24 on: 19/11/2013 21:51:45 »

 

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