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Are we at the centre of the Universe?


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I've looked but can't find an answer to this. I've read from lots of sources that 'we' believe that the edge of the Universe is 13.7 billion light years away. But in which direction? I can't see that mentioned anywhere.

Steve

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Hi Steve,

this is a common mis-interpretation of astrophysics, yet understandable.

The 'edge' of the universe (at some 13.7 Billion light years away) as we call it is the 'visible edge' of the universe. However, this is not the confines of the universe and the best way I can describe it is to use the view out to sea from a beach.

Your stood on the shoreline of a tiny island and you can see the horizon clearly circling 360 degrees (this is the visible edge), however the ocean doens't stop at the horizon does it, it continues for many more miles around the whole circumference. However in space the universe expands in every direction so in effect the visible edge is represented by a sphere 13.7 billion light years in radius.

BUT and there is a massive but here.........this is not how the universe works, there is no direction in space or an edge, you are quite right to think that if there is an edge then there is a centre and because we can see the edge at an equal point in every direction then we must be central. This is not right though. The universe is not expanding from a central point, it is expanding in every location in every direction.

Now this is quite difficult to not only explain (some of the best astrophysicists and cosmologists struggle) but to also understand and the most commonly used expression is the 'rising current bread' theory. Now imagine a cake or bread in the oven, dotted throughout with raisins/currants, the currents represent individual galaxies and as the cake heats up (i.e. as time goes on and the universe expands) the raisins become further and further apart from one another, yet there is no centre and each raisin suffers the same expansion as another one.

Its hard to explain (personally I hate the 'raising bread' example, its lame for such an important suject!) and understand as I have said but you have to understand that uniformly each galaxy (with some exceptions!) is moving apart from every other one which is proving universal expansion. It just so happens that the visible edge of the universe (13.7 billion light years) is the same unit as the age of the universe (13.7 billion years old).

Hope this clears things up a little.

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Excellent, thanks. But I had heard that the speed (relative to us) of the stuff at our visible edge is approaching that of light, thus making it almost the actual edge of the universe. Since if there was any stuff further than that, it would need to have travelled (or be travelling) faster than the speed of light to get there, no?

I've a feeling my brain might begin to hurt in a short while. :hello2:

Steve

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The short answer is no. And your brain will hurt if you try and take it on board. But it's a good pain, like the pain of having a snowball in your hand for too long or when you are spanked with a soft leather............................

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I think these claims of 'objects expanding away at the speed of light, or near it' are coming from the redshifts seen (might be wrong here).

For all its success, I think there is a flaw with the use of it, now I aren't an expert, far from it but I think that there may be an illusion slipping into place with redshift. We use it for distance marking objects and I believe that at large distances it doesn't work as it does in a more local vacinity. I aren't the only who who believes this, there are others (the people escape me atm, shall have to read up on it), but there is questions over how redshift theory works at very large universal distances, almost as if something interferes to give the illusion of distance.

I may be wholly wrong here, but its what I think.........no expert tho, so perhaps take this with a pinch of salt!

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Excellent, thanks. But I had heard that the speed (relative to us) of the stuff at our visible edge is approaching that of light, thus making it almost the actual edge of the universe. Since if there was any stuff further than that, it would need to have travelled (or be travelling) faster than the speed of light to get there, no?

"approaching" is ok. Physicists have been making electrons go at "almost" the speed of light for decades now. 95%, then 99%, then 99.9%, then 99.99% and so on. It's the nature of special relativity that there's a whole infinity of energies between 99.99% and 100% of the speed of light.

And it doesn't make it the "actual" edge of the universe because, according to theory, one would observe the same phenomenon no matter where one is in the universe. That just codifies our expectation that Earth is not privileged over any other bit of the universe. So, go to the apparent edge and you'd see other apparent edges and so on.

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I think you guys are over-thinking this. All you have to do is come on over to my place and meet my two year old. He will dispel every myth these astrophysicists have imposed upon us as to where the center of the universe is.

:crybaby: :whip2: :hello2:

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If the "apparent" edge is the same distance away in all directions doesn't it mean your essentially at the middle... A gross over simplification I know... but its a thursday morning haven't had clear skies for weeks and what little "brain" that I had is shutting down rapidly...

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The following is my understanding but I could have misunderstood what I read....

The Universe is infinite - it was immediately infinite at the time of the big bang 13.7 billion years ago. In all places within the Universe, space itself is expanding so that objects appear to be moving away from us. In fact, red shift at cosmological scales reflects the rate of expansion of space rather than the speed at which objects are moving away. Galaxies in our local group are gravitationally bound, so some are moving towards us and some away. All more distant galaxies ie outside our local group appear to be moving away due to this expansion of space.

The furthest we can "see" is 13.7 billion light years. So, if we look in one direction we can see galaxies 13.7 billion light years away - likewise if we look in the opposite direction. However, observers in those two extremes could not see each other because there has been insufficient time for light to have travelled between them. Our galaxy would appear to be at the edge of the Universe for both of them.

HTH

Mike

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So, is there is more stuff beyond the apparent edge, why can't we see it?

Steve

Because the light from it hasn't got here yet. The universe is expanding at one light year in every direction each year from our perspective, because that's the bit that we can see. If we could suddenly move several million light years, we'd see further in the direction that we had moved in, but the bit behind us would have gone.

Kaptain Klevtsov

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But how did the further away bits of the universe get there faster than the speed of light? Is this inflation coming in? In other words, in the early stages of the universe, the space in between (for example) our galaxy and those which are now over 13.7bly away, inflated faster than the speed of light?? And the light still hasn't managed to catch up? Will it ever?

Ah, we seem to be digressing a bit. :oops:

Funny, seems to be cosmo-theory day for me. :?

Andrew

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i But how did the further away bits of the universe get there faster than the speed of light?

a) they didn't have to "get there" because they didn't start from the same point as us.

:hello2: recession velocities can exceed the speed of light without the theory blowing up, they are "fake" velocities anyway.

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Because the light from it hasn't got here yet. The universe is expanding at one light year in every direction each year from our perspective, because that's the bit that we can see. If we could suddenly move several million light years, we'd see further in the direction that we had moved in, but the bit behind us would have gone.

Kaptain Klevtsov

If I've understood this correctly, what we consider to be the edge of the universe is merely the furthest we ourselves can see, but that will change relative to (dependant upon) our location, right?

Ok then, that means if someone was way out at the edge of 'our' known universe and they were looking back in our direction, we'd be at the edge of 'their' universe. And since they'd be at the center of 'their' universe, their opposite edge would be as far from them as we are, right?

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Because the light from it hasn't got here yet. The universe is expanding at one light year in every direction each year from our perspective, because that's the bit that we can see. If we could suddenly move several million light years, we'd see further in the direction that we had moved in, but the bit behind us would have gone.

Kaptain Klevtsov

If I've understood this correctly, what we consider to be the edge of the universe is merely the furthest we ourselves can see, but that will change relative to (dependant upon) our location, right?

Ok then, that means if someone was way out at the edge of 'our' known universe and they were looking back in our direction, we'd be at the edge of 'their' universe. And since they'd be at the center of 'their' universe, their opposite edge would be as far from them as we are, right?

Same horse different jockey...?

If the "apparent" edge is the same distance away in all directions doesn't it mean your essentially at the middle... A gross over simplification I know... but its a thursday morning haven't had clear skies for weeks and what little "brain" that I had is shutting down rapidly...

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Because the light from it hasn't got here yet. The universe is expanding at one light year in every direction each year from our perspective, because that's the bit that we can see. If we could suddenly move several million light years, we'd see further in the direction that we had moved in, but the bit behind us would have gone.

Kaptain Klevtsov

If I've understood this correctly, what we consider to be the edge of the universe is merely the furthest we ourselves can see, but that will change relative to (dependant upon) our location, right?

Ok then, that means if someone was way out at the edge of 'our' known universe and they were looking back in our direction, we'd be at the edge of 'their' universe. And since they'd be at the center of 'their' universe, their opposite edge would be as far from them as we are, right?

Yup.

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Because the light from it hasn't got here yet. The universe is expanding at one light year in every direction each year from our perspective, because that's the bit that we can see. If we could suddenly move several million light years, we'd see further in the direction that we had moved in, but the bit behind us would have gone.

Kaptain Klevtsov

If I've understood this correctly, what we consider to be the edge of the universe is merely the furthest we ourselves can see, but that will change relative to (dependant upon) our location, right?

Ok then, that means if someone was way out at the edge of 'our' known universe and they were looking back in our direction, we'd be at the edge of 'their' universe. And since they'd be at the center of 'their' universe, their opposite edge would be as far from them as we are, right?

Same horse different jockey...?

If the "apparent" edge is the same distance away in all directions doesn't it mean your essentially at the middle... A gross over simplification I know... but its a thursday morning haven't had clear skies for weeks and what little "brain" that I had is shutting down rapidly...

You would be in the middle no matter where you were.

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>they didn't have to "get there" because they didn't start from the same point as us.

>Separate points, but the distance between them tends to zero as time goes to back to big bang

Can you reconcile these two for me. I'm just getting confused, now. Doesn't a zero distance mean the same point?

>recession velocities can exceed the speed of light without the theory blowing up, they are "fake" velocities anyway

Could you expand any on this?

Thanks,

Steve

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Can you reconcile these two for me. I'm just getting confused, now. Doesn't a zero distance mean the same point?

Mathematically speaking, not necessarily. The point is that nobody knows exactly how we should model spacetime, especially for a model that would include the moment of the big bang. There are "semimetric" spaces where there is a well-defined distance measure but zero distance does not imply coincident points.

But this is not the meat of the point, as I see it. Our models only make sense as we evolve the equations backwards in time. Points in the universe get assigned an ever closer distance. Mathematically, at the point of the big bang, they seem to coincide, but we would be foolish to assume that the equations retain their familiar form to the last. So I don't really care what they say about the origin itself, we already know that they are incomplete and inconsistent ("wrong", in other words).

Could you expand any on this?

only with decreasing confidence but the way I understand it is that relative velocities make sense at one space time point. That is like a collision event, say, particle A comes from direction x with speed v and particle B comes from direction y with u. The recession velocities are attached to separate events, billions of light years apart: galaxy A over HERE and galaxy B way over THERE. If we saw a galaxy collision event where the pyrotechnics imply greater than light speed velocities, that would be a different thing, as they would be happening at the same point in space and time and that WOULD be a violation.

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zero distance does not imply coincident points.

At this point, I'm going to have to throw my hands in the air and give up. I can't see me ever getting my head around that :hello2:

Its a strange world indeed.

Thanks anyway,

Steve

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Would it help if you visualised a pair of lines crossing? You can say that there is a common point to both lines or that each line has a point that is at zero distance from a point on the other line. It looks to me like you would not lose anything by the second description.

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