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Wondering something about the expansion of the universe


smulx
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I've wondered this for a while but I've never got around to trying to find out the answer. Firstly, people say that the furthest distance we'll ever see would be 13.7bn light years because the light from anything beyond this wouldn't have had time to reach us. But with the universe being estimated at 13.7bn years, wouldn't that mean that there isn't anything to see before this time?

I hope that makes sense. The next part feels a bit harder to explain. I also understand that this 13.7bn light year limit applies to all directions. I read that there's an imaginary sphere that extends 13.7bn light years from us and we couldn't observe beyond that for the reason I just stated. But what I don't understand is why this distance is the same in all directions. Since all the matter of the universe began at a single point in space 13.7bn years ago, why can we at this point in space see that far in all directions? Surely nothing existed in certain directions all that time ago.

This is probably a stupid question and I have a feeling I'm just misunderstanding something, but hopefully someone will be able to explain.

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I think that although the "Universe" might be 13.7 Bn years old, space-time expands so that the furthest objects from us are actually more than 13.7 Bn light years away. It is a bit of a struggle to imagine this sort of thing.... Einstein's Telescope by Evalyn Gates is an interesting read on this subject.

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the obvious flaw in the concept of our universe being 13.7billion years old and that we cannot see further that that point is that ........ if the start point was the centre of a sphere 13.7 billion years ago, why can we not see the other side of the sphere which in theory reaches out to 27.4 billion years.the other obvious flaw is that it is assumed that we are at some point within that sphere on on its surface.

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I'm not convinced on being on the skin of anything at the moment and i'm sure the 13.7bn yr life of this universe will be revised over and over as time passes until we will find out anything more.

For me so far I see a bubble, us inside somewhere .... kinda like the bubbles in this video LiveLeak.com - Water Bubbles in Space

Lawrence Krauss's Universe From Nothing is a good one for this :)

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I think there are quite a few misconceptions here, not surprizingly given the nature of the beast. I may well add to them in what follows!!

-The 13.7 billion years is the light travel time for the photon sent out by the distant object. The distance to that object is now far greater than 13.7 billion lightyears because during the 13.7 billion years flight time the universe has been expanding.

-So what is the distance now? This is problematic because of the relativistic issue of simultenaity. Different observers cannot agree on when 'now' is... Great, innit! There is a conventional way of agreeing on the distance. But I've forgotten it. Sorry! (Get 'im off!!)

-The observable universe has a limit, a 'horizon', because at a certain distance the accumalated expansion of the universe means that objects beyond this point are receeding faster than light so their light never arrives.

- The moment you start talking about seeing from one side of the universe to the other you are doomed because it does not have sides. Nor does it have edges or a centre.

This can be dealt with by the balloon analogy. A balloon has a centre and a suface so you can look from one side, through the translucent skin, to the other. The universe is NOT like that. The universe is considered to be like the SURFACE of the baloon ONLY. You must remove all other dimensions in the analogy and keep them out of it. No one point on the surface is different from any other. There is no centre to the surface, no edge, no boundary. When the surface expands it does not expand from a centre but everywhere at all times.

Most conceptual problems regarding the big bang come from thinking of it like an expanding balloon when in the BB theory the universe is only like the surface of the ballon. If you mis-read this aspect of the analogy you will never get it. In fact I doubt that anyone really 'gets it' in the way that we can conceptualize our more local circumstances... That is where our brains evolved. Local brains for local people!!

Where's the Christmas pud?

Olly

Edited by ollypenrice
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If that is the case then Olly, this is what I can't get my head around.....

From the beginning point, the first expansion, by theory, would have expanded from a single point, therefore there is surely a single point which is exactly the center. If everything is expanding and accellerating away then that single point would still exist, just be extremely hard to pinpoint lol.....

Finding it is a different beast lol.

As I said earlier, where my head is at at the moment, I'm currently thinking the Universe is a Bubble, we are inside the bubble, the bubble is expanding in all directions and this bubble, probably is part of another bubble or one of many bubbles. Kinda like a load of biodomes floating around in the greater nothing. The odd collision here as in the latest CMB data showing possible contact rings.

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I myself love reading about this. I have trouble picturing the shape of our universe and where we are in it. I can't not get my head around the fact there is no edge. If we are expanding I question what are we expanding into. ??? I cant get my head around .... No centre ...

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Re: Expanding into .... nothing. Space and Time, the universe is expanding as a whole, apparently there was nothing to expand into, this expansion created everything we know, anything outside, is currently classed as nothing, which is something haha.

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If we are expanding into nothing that's fine. I just can't get my head around the fact the big bang was from something. So where did all that material come from. ?? Therefor could there still be something ?? Sorry if that sounds poor but hard to explain what I mean

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The whole 'expanding' concept seems to be based on the idea that people have in their heads of an explosion, exploding into something.

Statements like.....after 'x' milliseconds the universe was the size of (insert everyday object) seem also to me to be misleading.

If all of space and time came into being at the moment of the big bang, then to use the concept of size is clearly wrong. The universe itself has always been the same size....the size of the universe.

What we regard as expansion is the change in relationship between the stuff that the universe contains, not a change in the size of the universe itself, as you can't give it a size as there is no relationship to anything outside it by which it can be measured.

Oooh....my head is hurting :):D:D

Cheers

Rob :p

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From the beginning point, the first expansion, by theory, would have expanded from a single point, therefore there is surely a single point which is exactly the center. If everything is expanding and accellerating away then that single point would still exist, just be extremely hard to pinpoint lol.....

No. I think that's the most common misconception when trying to imagine this. It is that point itself that expanded. The expansion of the universe creates space (and time). There is no "outside" that point. We are inside the expansion. If that makes any sense... :)

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There are many clever arguments about the 13.7bn light year thing, plus the universe being 78bn light years wide (If it is, then something is moving faster than the speed of light at some point). Add to that, the big bang (if they don't want us to think of it as an explosion then why oh why call it the big bang????). I keep thinking that the big bang is explained in such a way that it sounds plausible, but then again, perhaps not.

The simple truth of the matter here is that a lot of it is pure speculation no matter how much science they try to draw on. As this speculation is delivered by minds far superior to most of us, it quickly becomes embedded into the human psyche as fact, when in fact, it's not fact......

What nobody can explain is how can a massive object, or a huge pile of dust materialise from nothing. The catch them out question, is "what was there before the big bang?". They can't anwer that one other and will never be able to.

The speculation is entertaining. Certainly plausible of course, perhaps even right. Einstein and others are quite clever guys. Bit one thing fellas, please explain to me how a massive object can perhaps move faster than the speed of light? If the universe is so big and the big bang happened, the maths don't stack up. 78bn light years cross is a hell of a lot older than the max age we are quoted of 13.7bn light years. Just doesn't do it for me, no matter what the explanation is.

We'll all say worm holes exist next.

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There are many clever arguments about the 13.7bn light year thing, plus the universe being 78bn light years wide (If it is, then something is moving faster than the speed of light at some point).

That is not a violation of Einstein's "speed limit" by the way. 2 objects that are so far apart that they are behind each others observable universe horizon can have no causal relationship with each other. Therefore you can't say they are moving away from each other with a speed greater than that of light.

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Nope you're all wrong - the Universe is shaped like the end of a tuba - there was a picture of it in Sky at Night last year lol :p

So that's where that horrible noise is coming from....and I thought it was the kid next door with his new keyboard :)

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I thought the observed superluminal motion of very distant galaxies was not in violation of the cosmic speed limit. This is because that it isn't the galaxies themselves that are moving but the space between them expanding, and the larger the distant between the observer and the galaxy the higher the observed speed.

The redshift value of galaxies travelling at the speed of light is around z=1.4, where z is redshift. The deeper you look, the higher the redshift and the quicker it increases per unit of distance, it's like an ever steeping slope. It can be compared to approaching light speed, you can keep on accelerating but will never quite get there. The redshift of the Big Bang is z=∞

Have a look at the bottom part of this message where it gives examples of high redshift galaxies and their light travel distance.

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Yes Yes has it. Yes yes indeed!

Let's just say this again; the universe did not expand from a point. The universe was a point and the point expanded. You absolutely must get this for anything that follows to make sense.

Why is it called the Big Bang if it is not an explosion? The name was invented by Fred Hoyle, who did not believe in the theory but had an elegant Steady State theory in which slow expansion was allowed. The name is intended to satirize the expansion theory but Hoyle's irony is now turned into a double irony by believers who continue to use the term.

The theory is not pure speculation. It has massive observational evidence in its favour and originated in observations started by Vesto Melvin Slipher (the best name in astronomy??) and continued by Hubble and Humason. But that does not make it correct, of course. The more extreme the physical circumstances (as in the inferno of the early universe) the less we can rely on the physics of here and now.

The question 'what happened before the BB' does not, in fact, catch anyone out and will never be answered because it is, itself, self contradictory and meaningless. Why? In order to ask the question you have to believe in infinite time. If you do, then you don't believe in the BB. You cannot insert the BB theory into a theory of infinite time because in the BB infinite time does not exist. It is philosophically impossible to consider both BB and infinite time in the same model of the universe. It is like sayiing, 'If unicorns don't exist, what colour are they?'

It is, however, quite possible to talk about something 'outside' the BB but such talk must be speculative. Lee Smolin's Life of the Cosmos is a gloriously seductive piece of speculation along these lines.

Matter moving faster than the speed of light? It does and it doesn't. There are two kinds of 'movement' here. Imagine coins resting on the surface of a balloon. You can slide them around. That is movement in the usual sense. Now glue them onto the surface of the balloon. The surface (again, the surface only in the analogy) is space. Blow in the baloon and the galaxies (which can't 'move' because they are stuck down) still move apart. It is only this second kind of 'movement' which can exceed the speed of light. No violation of Einsetein.

The problem is time. No one understands it and the great physicists know better than all the rest of us that they don't. Feynman discovered that a positron cannot be distinguished from an electron travelling backwards through time. And vice versa.

Firing photons one at once through two slits produces interference. Maybe the photons don't know they are supposed to be fired one at once??? Maybe time for them is not what it is for us?

Who started all this??? Gerrim!

Olly

Edit Excuse me Hypernova, we crossed in the post. We make the same point.

Edited by ollypenrice
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In simple terms.

Everything happend everywhere and is expanding from everywhere.

thats how i see it anyhow.

For any observer anywhere the expansion is the same.

we only look at things naturally from an observers view, but it helps to look at the observer and other relative observers view to get a better picture

Edited by Earl
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Yes Yes has it. Yes yes indeed!

Let's just say this again; the universe did not expand from a point. The universe was a point and the point expanded. You absolutely must get this for anything that follows to make sense.

I get that point, that's not what i'm talking about.

What I am saying here is that if the universe was a point and it expanded in all directions including time. Then firstly, what was the shape of this point, if it was in fact a point (small infinitely small round blob itself, then it would have had a central point inside. Even if it expanded internally in all directions to become what we would now, there still should be a measurable center point, probably not for us due to distances and all the other universal hullaballooo lol....

Haha, this is too damn confusing, i've drawn out loads of different little idea's and gone over and over it. I can accept pretty much most theories other than god creating it a couple of thousand years ago lol. But accepting the theory and actually making it work in the constraints of the human mind is a bit of a mind bender lol.

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In simple terms.

Everything happend everywhere and is expanding from everywhere.

thats how i see it anyhow.

For any observer anywhere the expansion is the same.

It's true to an extent only that the initial expansion happened everywhere but the current observed expansion isn't happening everywhere. The galaxy clusters may be getting further apart, but the galaxies local groups like ours are bound to each other and are getting closer to each other. So I wouldn't say "Everything happened everywhere and is expanding from everywhere".

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I get that point, that's not what i'm talking about.

What I am saying here is that if the universe was a point and it expanded in all directions including time. Then firstly, what was the shape of this point, if it was in fact a point (small infinitely small round blob itself, then it would have had a central point inside.

If you have an infinitely small point, how can it have another point inside? :) A point is a point.

Also, don't imagine this as an expanding ball / balloon which would of course have a centre. It's more like the stretching of a rubber sheet (as a two dimensional representation). If you ignore the edges of that sheet for a moment, when you strech it, the stretch itself has no centre. It stretches equally at all locations.

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Where is the centre of the surface of a balloon? (not where is the centre of a balloon.) There isn't one.

You are imposing on the universe the idea of its having a shape. But - this is a new line of thought for me so bear with me - it seems to me that a shape is defined as a form within space. Sit inside a cube, in the middle. Send out rays in all directions until they hit a wall (a boundary) and cut them off there. So if you know how long each ray is you can define the size and shape of your cube. (Well, if it is a cube it is a cube, but the point is clear, I hope.)

If you did the same from the inside of a giant rugby ball then the rays would be cut off at different lengths when they met the leather boundary and now your rugby ball shape and size would be defined and measured.

Now then, now then, if the rays are never cut but go on forever, what shape do they diefine? They don't, because they are never cut. A sphere? No because the rays never reach the surface of a sphere to be cut. So only something finite can have a shape. By definition something infinite cannot. Actually, in cosmology the term infinite alone will not quite do. You can have a model universe that is infinite, or one that is finite but unbounded. But I think my point will work for both. You only meet a shape when you meet a boundary. If you don't meet a boundary you never encounter a shape. The universe does not have a shape.

If this is unpalatable, here are two great quotes. Einstein; 'Common sense is just the name given to that set of prejudices accumulated by age 18.'

And better still, Neils Bohr to Einstein when Einstein said, God does not play at dice.

Bohr; Stop telling God what to do.

(The God in question was not, I think, God in the usual sense but rather more like 'reality.')

We see the universe in human terms with human minds in human language. The Universe, however, can be whatever it wants to be and if we don't get it, tough!

This was Bohr's point, I think, and it is very, very deep.

Olly

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