# Does this contradict the expansion of the universe?

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Expansion happens everywhere, the universe is already too big to traverse at the speed of light in the time it's existed and bits are receding from other bits 'faster than light' - so we can consider it infinite in size, well at least until we invent that faster than light speed drive...

I love this stuff but unfortunately am not the sharpest tool in the box. Light speed is a speed limit according to our current understanding. So presuming we could get to that limit, would we not be breaking that limit as we traverse the expanding space from the aspect of the observer? We observe the limit being broken, so in essence it can be broken? I understand that this is more like light laying down extra tracks behind it rather than going faster as such, but, essentially it is going faster against the backdrop of the container space occupies. When I say container I am presuming that is an infinite body (for want of a better word) that space can expand into because if space itself were infinite (without the container) surely it would not be expanding as it would already occupy everything?

Sorry, that probably makes no sense to educated minds, please be gentle with me, yes, I am out of my depth

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I love this stuff but unfortunately am not the sharpest tool in the box. Light speed is a speed limit according to our current understanding. So presuming we could get to that limit, would we not be breaking that limit as we traverse the expanding space from the aspect of the observer? We observe the limit being broken, so in essence it can be broken? I understand that this is more like light laying down extra tracks behind it rather than going faster as such, but, essentially it is going faster against the backdrop of the container space occupies. When I say container I am presuming that is an infinite body (for want of a better word) that space can expand into because if space itself were infinite (without the container) surely it would not be expanding as it would already occupy everything?

Sorry, that probably makes no sense to educated minds, please be gentle with me, yes, I am out of my depth

- I draw a line with a pen on a piece of paper and it takes me 1 second to draw that line.  I next measure the length of the line and it is 10cm long.  So the speed of the pen was 10cm per second.

- I draw a line on an elastic band moving the pen at exactly the the same rate as above.  Again it takes me 1 second to draw that line.  I now stretch the elastic band, and then measure the length of the line and find it is 20cm long.

- In both cases I moved the pen at a speed of 10cm per second, but because I stretched the elastic band, and then measured the length of the line it looks like the speed of the pen was 20cm per second, but it wasn't, it was 10cm per second.

That is pretty much what is going on with light speed and the expansion of the universe.  The maths is more complicated because the elastic band was stretching as I drew the line, and continues to stretch even after I stopped drawing, but nonetheless it is a good analogy.

Edited by IanL
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Steady state and bouncing universes are different and certainly the steady state theory is very obsolete now, no recent evidence supports that and most contradicts it, it's essentially been abandoned as plausible.

Which is a pity. I rather liked that idea as a boy. Then again I just liked Fred Hoyle's maverick style

There is something alluring about the Steady State theory. No need for an origin. It is and will continue to be! I found that more acceptable than a Big Bang.

Maybe it's just gone out of fashion and like all fashions come back round again

So long as there's no Strings n'things in a Steady State universe It'll continue to have a place in my heart

Edited by Paul M
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- I draw a line with a pen on a piece of paper and it takes me 1 second to draw that line.  I next measure the length of the line and it is 10cm long.  So the speed of the pen was 10cm per second.

- I draw a line on an elastic band moving the pen at exactly the the same rate as above.  Again it takes me 1 second to draw that line.  I now stretch the elastic band, and then measure the length of the line and find it is 20cm long.

- In both cases I moved the pen at a speed of 10cm per second, but because I stretched the elastic band, and then measured the length of the line it looks like the speed of the pen was 20cm per second, but it wasn't, it was 10cm per second.

That is pretty much what is going on with light speed and the expansion of the universe.  The maths is more complicated because the elastic band was stretching as I drew the line, and continues to stretch even after I stopped drawing, but nonetheless it is a good analogy.

Yeah I understand that (well...I think I do ) my thought was more that; while the band is stretching and the pen is moving, to the back drop the pen is doing 20cm per second. So if space is expanding into a container that is infinite, from the container point of view light is breaking it's limit. Also, if space IS the container then it has nothing to expand into as it is already infinite, if it is infinite how can it expand?

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Sorry, I am really not academic, can't stress that enough. I am however extremely curious about this subject. As I realise I may be asking questions that are purely academic and can be answered by methods I would not understand I will welcome any comment but would prefer not to derail a great thread

So feel free to sigh, roll eyes and move on

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I can see what you are thinking.

How do we really know how big the universe is? It's being measured by the furthest objects that we can see / detect all based on their distance which takes us back to the beginning of the universe. But as we can't see dark matter / energy, we only know that it is there as the stuff the fills all the spaces, how do we know how far beyond those objects that we can see in the far distance that the dark stuff actually goes? We are only treating the size of our universe as the stuff we can see and not what we can't see.

I suppose another way to ask the question is say that the entire universe that we can see and measure sits on the size of my coffee table, that coffee table sits in my living room, how do we know that the whole living room is not the dark stuff which is all part of the universe, how do we know that the universe of dark matter doesn't take up my entire house, street, town, county or country? I don't think we can really give a measurement when there is the dark stuff we can't see, so we can only give a measurement on what we can see.

Yes the universe is expanding on what we can see, but is it really expanding or is it just spreading in to the dark space that we can't see.

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I love this stuff but unfortunately am not the sharpest tool in the box. Light speed is a speed limit according to our current understanding. So presuming we could get to that limit, would we not be breaking that limit as we traverse the expanding space from the aspect of the observer? We observe the limit being broken, so in essence it can be broken? I understand that this is more like light laying down extra tracks behind it rather than going faster as such, but, essentially it is going faster against the backdrop of the container space occupies. When I say container I am presuming that is an infinite body (for want of a better word) that space can expand into because if space itself were infinite (without the container) surely it would not be expanding as it would already occupy everything?

Sorry, that probably makes no sense to educated minds, please be gentle with me, yes, I am out of my depth

AIUI the point is that while nothing can travel through space faster than the speed of light there is no limit to how fast space itself can move.

An analogy would be throwing a cricket ball. You might be able to throw a ball at 100km/h which for the purpose of our analogy is the speed of light. If you throw the ball toward me I would Measure its speed as 100km/h. What would happen if you were on a train moving away from me at 50km/h? The train here is analogousto expanding space. Now I would measure its speed as 50km/h even though you threw it at 100km/h. In the wierd world of relativity and light that would equate to a redshift. Now what would happen if you threw the ball away from me while you were on that train? Classically I should see it recede at 150km/h and so break our universal speed limit. But how would you get information from the ball on the train to us? You can only send information at 100 km/h so we could never see the speed limit being broken. At no point has anything moved faster than 100km/h.

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AIUI the point is that while nothing can travel through space faster than the speed of light there is no limit to how fast space itself can move.

You can only send information at 100 km/h so we could never see the speed limit being broken. At no point has anything moved faster than 100km/h.

Then in that case I didn't throw the cricket ball away from you at 100km/h +50km/h train speed? Are you saying that we can break the speed of light but never observe it or that the limit of information will somehow shave that extra 50km/h off my cricket ball? Or is this where time kicks in and I start to hum the theme tune to the chuckle brothers?

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Then in that case I didn't throw the cricket ball away from you at 100km/h +50km/h train speed? Are you saying that we can break the speed of light but never observe it ...

Compare it to the difference between the size of the observable universe and the size of the universe. Just because the observable universe is 14 billion ly in radius doesn't mean that it couldn't be much much larger. We can't seethose regions because the space between those two point is growing faster than light and we can only communicate at light speed.

If you want to see how light speed might be overcome then look up alcubierre drives (essentially a pocket bubbleof space time that expands locally faster than light while anything in the bubble moves belowlight speed

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Thank you for bearing with me jnb, Langy and IanL, really appreciate the replies. jnb, I think I'm grasping what you are saying, I will go away and check out your recommendation.

Sorry for jacking the thread temporarily

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Thank you for bearing with me jnb, Langy and IanL, really appreciate the replies. jnb, I think I'm grasping what you are saying, I will go away and check out your recommendation.

Sorry for jacking the thread temporarily

I shouldn't worry as I was asking questions too.

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Yeah I understand that (well...I think I do ) my thought was more that; while the band is stretching and the pen is moving, to the back drop the pen is doing 20cm per second. So if space is expanding into a container that is infinite, from the container point of view light is breaking it's limit. Also, if space IS the container then it has nothing to expand into as it is already infinite, if it is infinite how can it expand?

I see what you are struggling with here.  Two things:

- There is no "from the container's point of view".  Everything that can be observed and everything that can do that observing is in the container.  Or to keep my original elastic band analogy going, you and the line are both on the elastic band.  You are imagining the situation from the point of view of a 'god like' observer looking down on the band from above.  Theological questions aside, there is no possibility of you 'getting off' the elastic band to look down on it, you can only ever observe from your position on the elastic band.

Once you grasp that, I hope you can see that the only way for you to deduce that the elastic band has stretched is that the line appears to have been drawn faster than the speed limit of the pen will allow.  If you accept that the pen cannot move faster than 10cm per second (which you must), then the only way you can create a 20cm line in one second is if the elastic band stretches whilst you are drawing it.  That is one of the things relativity demonstrates.

- The whole 'what is the universe expanding in to' question is hard to get one's head around.  Again, forget the notion that you can 'get outside' and look down on the universe.  The universe is all there is*, it doesn't have to expand "in to" anything.  It just is.

* Ok so there are lots of theories about multiverses, branes and so on that try to explain how the universe came in to being, but the point is we can't get outside the universe to test them.  Nor can the "outside" (if such a concept is even meaningful) get in to affect us, so to all intents and purposes there is no "outside".

Edited by IanL
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Thanks for taking the time to explain further, I actually understand this now, or rather, I understand the points you are conveying

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I love this stuff but unfortunately am not the sharpest tool in the box. Light speed is a speed limit according to our current understanding. So presuming we could get to that limit, would we not be breaking that limit as we traverse the expanding space from the aspect of the observer? We observe the limit being broken, so in essence it can be broken? I understand that this is more like light laying down extra tracks behind it rather than going faster as such, but, essentially it is going faster against the backdrop of the container space occupies. When I say container I am presuming that is an infinite body (for want of a better word) that space can expand into because if space itself were infinite (without the container) surely it would not be expanding as it would already occupy everything?

Sorry, that probably makes no sense to educated minds, please be gentle with me, yes, I am out of my depth

Hi,

sorry missed there was more activity on this thread.

I think it's best to think about c, the speed of light as a limit for velocity that can't be crossed (or even reached for anything with rest mass).

The expansion of the universe is not really speed or velocity, it is a stretching of the fabric. Two points far enough on the fabric can be (apparently) moving due to this stretching at a rate at or faster than light without contradicting Einstein's relativity and the limits on local velocity limited by the speed of light.

What it means though is.

a) there's a limit on what part of the universe we can see. Centred on us (or any observer in fact in any location) imagine a sphere that is the observable universe, you can see to the edge of the sphere that represents points receding at the speed of light from us - the observable universe. Interestingly the light from those points still travels and arrives to us at the speed of light, it's just red-shifted further and further to longer wavelengths, until eventually it stops being a detectable light wave.

even if you can see it, you can't get there by conventional travel (sub light-speed) - if parts of the universe recede faster than light you'd need more time than the length of the universe to get there and since they continue to recede from us (currently believed to be at an ever accelerating rate of expansion) that's always going to be the case.

So in summary, there are parts of the universe unreachable to us and worse still, un-observable to us! and the universe is stretching, expanding at an ever accelerating rate, so what is contained in the observable universe is likely to thin out on the grand scale (on the smaller scale galaxies and clusters will remain gravitationally bound) - so you could imagine an ever thinning, wispier sponge being ever and increasingly stretched out over time.

Nothing with rest-mass can travel with peculiar velocity above c (peculiar, which is the proper name, think of it as relative to the underlying fabric of space). Parts of space can however be expanding away from us (and carrying galaxies contained there) much faster than c (as observed by us) with no contradictions at all.

The standard analogy is the balloon model. You're on a balloon's surface and can move around (peculiar motion), but if at the same time that balloon is being inflated then it will appear that where you are things are moving away and points furthest away on the other side of the balloon might appear to move faster than your physics allows...

If it is a balloon, lets hope it doesn't pop any time soon...

Edited by LouisJB
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So in summary, there are parts of the universe unreachable to us and worse still, un-observable to us! and the universe is stretching, expanding at an ever accelerating rate, so what is contained in the observable universe is likely to thin out on the grand scale (on the smaller scale galaxies and clusters will remain gravitationally bound) - so you could imagine an ever thinning, wispier sponge being ever and increasingly stretched out over time.

This expanding/stretching is another thing I cannot get my head around. If gravity can overcome the effect of expansion then how can galaxies be moving away? Gravity is exerting a force on all matter everywhere (albeit incredibly weak at distance but still a tangible force?) so unless we are saying that expansion has a force to counter gravity, why is stuff moving apart? If expansion has a force and is not just space stretching or more nothing coming into being then it is, something? My brain is approaching BSoD

I just don't get space.

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I think it is the dark unseen stuff that is actually expanding, pushing everything apart. Now that dark stuff also has it's own gravitational pull on things as it is that which keeps the galaxies etc together.

For example our galaxy is orbiting around the inner part (which I believe is a black hole) now everything else around that is orbiting at the same speed regardless of mass. In theory if that was to happen in our own solar system then the heavier or objects further away would shoot off as they would break orbit.

Outside our galaxy the dark stuff is keeping all those objects stuck in our galaxy.

Now we don't know what makes up the dark stuff but that is just getting bigger, it maybe that what is making it up is either just expanding in size like the rubber band theory or it could be like something we know grows in that the unknown stuff is growing in size to expand it.

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well that's what gravitationally bound is, galaxies close enough together will feel force of gravity due to their masses that will keep them from drifting apart. Similarly even stronger forces keep atoms bound and sub-atomic particles bound, so the expansion happens but things with stronger binding force don't get ripped apart or stretched directly.

Why is there expansion - well that goes back to things like dark energy and so on as discussed earlier in the topic.

In the beginning (so some interpretation of the big-bang theory says) everything was driven apart by pressure, pressure caused by extreme temperatures and radiation pressure which literally caused a big explosion. Now much later that sort of driving force is not dominant. Gravity is the main player at large cosmic scales even though it's by far the weakest force.

Since gravity is so weak and current theory (a theory attempting to explain accelerating expansion) suggests some constant repulsive force is pushing things apart at the large scale (not you or I or the solar system or galaxy etc). Some sources of this include vacuum energy (which can actually be seen/measured) and some unknown other energy (like dark energy) - but the exact nature of these things is not known (so we don't really know if these ideas are correct).

Some of this was sort of discussed at the start of the thread in response to the OPs questions. There's quite a few aspects to consider really, more than a few words here can really do justice to.

Out of all the things it's worth reiterating two important concepts.

1: expanding universe does not imply more "stuff" is being created

2: expansion due to dark energy etc is thought to be constant i.e. same amount per cubic meter today as when the universe was just 1 cubic meter, or any time in-between or in the future. You can see from this intrinsic property of energy in space that it becomes dominant as time progresses, matter gets less dense and there are vastly more cubic meters for repulsive energy to come from.

Hope that helps a bit. There's many ways to interpret this stuff and undoubtedly things will change as more discoveries are made. That's the thing, we keep asking and observing/experimenting and gradually more properties of the universe are uncovered...

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I think it is the dark unseen stuff that is actually expanding, pushing everything apart. Now that dark stuff also has it's own gravitational pull on things as it is that which keeps the galaxies etc together.

For example our galaxy is orbiting around the inner part (which I believe is a black hole) now everything else around that is orbiting at the same speed regardless of mass. In theory if that was to happen in our own solar system then the heavier or objects further away would shoot off as they would break orbit.

Outside our galaxy the dark stuff is keeping all those objects stuck in our galaxy.

Now we don't know what makes up the dark stuff but that is just getting bigger, it maybe that what is making it up is either just expanding in size like the rubber band theory or it could be like something we know grows in that the unknown stuff is growing in size to expand it.

not sure that's really quite right. There are two distinct types of dark stuff.

Dark energy is thought to be the primary cause of expansion.

Expansion affects everything (dark or otherwise, but some things are tightly bound so don't get affected).

Dark matter is matter i.e. something with mass obeying gravity (but maybe _not_ baryonic) that is needed to account for the characteristics of matter seen at large scales like galaxies, where we see rotation not exactly in-line with what you can explain by gravity and the visible matter we can observe alone.

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So can we see what makes up dark matter and dark energy?

If we can't then how do we really know that they are two different things other than that they behave in two different ways.

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no, not really, that's one of the big unknowns really. There are some things that are candidates for them, but nothing to account for all of it.

it might be it doesn't really exist and actually our best theories are wrong...

we "think" they are different because they must have distinct properties, one like matter causing gravitational contraction and the other like energy causing outward pressure

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Ok, thanks for the crash course I actually get what you are saying and feel happier knowing that we don't really know for sure, at this point I look over to people like you and say "sort it out"...job's a good'un.

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Think this documentary will explain a lot.

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I have some more questions which are all related to the expansion of the universe.

Since taking up astronomy this year I spend a lot of free time watching YouTube videos (preferably documentaries) on anything from the Solar System, Comets, Asteroids, Black Holes, Universe and some of the scientist like Einstein and much more.

With the expansion of the universe the best viewing that I have seen to explain this was having a room with chairs evenly spaced out in their rows and columns. As the room (universe) expands the chairs all get drawn apart so that they stay in their tidy columns and rows being equal space apart. I know that objects in the universe are not equally spaced apart but the point of the explanation was that the gap between each item increases at the same rate. Basically in a few hundred billion years if life is still about we will have difficulty seeing anything other than our own galaxy as everything else will have drifted further away due to the dark energy.

With watching several videos on our solar system they all talk about our sun formed nearly 5 billion years ago and it will be around another 5-6 billion years before it finally runs out of energy and dies. Quite simple that one.

Now when I watched videos on our galaxy and covering some of our neighboring galaxies I got a good tour around our galaxy as to how insignificant we are within our galaxy alone. In at least one of the videos they covered Andromeda which is supposed to be heading towards our galaxy. Predictions are given that in another 2.5 billion years Andromeda will finally collide with our galaxy. Initially it will rip right through our galaxy from one side to the other and then the gravitation pull between the two galaxies will pull them back together and eventually form one new larger galaxy.

So these different documentaries covering information on different aspects of the universe then make me ponder on new questions.

Firstly if the universe is expanding at an ever increasing rate making the objects all drift apart further how is it that Andromeda will still collide with our galaxy? Is it that the expansion rate even increase over the next few billion years will still be far slower that the rate at which the two galaxies are moving towards each other?

Secondly relating to life of the sun. If the two galaxies do collide what will that chances of our sun even surviving these next 5-6 billion years thus ending its life as a star?

What would be interesting if we were a fly on the wall aspect as to what will actually happen to our own solar system if and when the collision actually happens. Will everything just be wiped out back into small particles and consumed by the highest gravitation object? Should the sun and planets survive the collision will the earth end up the other side of the newly formed galaxy to our own star? I would guess that if this were to ever happen that being so far away in the future that no computer could even calculate the location of the objects as this happens with so many different factors that could change before and during the collision.

Now a different question relation to the dark matter keeping our galaxy together. At what rate is our galaxy spinning around its core? I know that the dark matter is keeping all the objects in place meaning that the outer objects of our galaxy take the same amount of time to do a full rotation as the center objects (with maybe the exception of the very closest objects to our black hole core) but how long is one rotation?

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Paul as I understand it   our galaxy takes 225 million years to do a turn.  The boss Sir PM told me that

As for the collision it seems to me that there is such a high percentage of nothingness in both Andromeda and the Milkyway that very little will actually collide.  And if my search for eternal life works out, currently based on consumption of real ale, I'll let you know in a few billion years

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Firstly if the universe is expanding at an ever increasing rate making the objects all drift apart further how is it that Andromeda will still collide with our galaxy? Is it that the expansion rate even increase over the next few billion years will still be far slower that the rate at which the two galaxies are moving towards each other?

Secondly relating to life of the sun. If the two galaxies do collide what will that chances of our sun even surviving these next 5-6 billion years thus ending its life as a star?

What would be interesting if we were a fly on the wall aspect as to what will actually happen to our own solar system if and when the collision actually happens. Will everything just be wiped out back into small particles and consumed by the highest gravitation object? Should the sun and planets survive the collision will the earth end up the other side of the newly formed galaxy to our own star? I would guess that if this were to ever happen that being so far away in the future that no computer could even calculate the location of the objects as this happens with so many different factors that could change before and during the collision.

Regarding your first question, you are correct.  Gravity will keep the 'local' universe together on a pretty large scale - there will be lots of galaxies in this local area but it will become isolated from other areas as the universe expands.  Using your chair analogy, the chairs get further apart but the atoms making up the chair stay together (different forces involved, but the idea is the same).

Regarding galaxy collisions, you might imagine two clouds of smoke crashing in to each other.  You end up with one cloud of smoke, but the atoms/molecules in the smoke don't annihilate each other in some massive crash-fest as it is still mostly empty space.  I once heard someone describe it like this:  The chances of two stars colliding during a galaxy merger are much smaller than two moths flying randomly around in a football stadium crashing in to each other.

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