Centre of ?

[Brian W (Brian)]

Every-where is the 'centre' of the universe. I certainly can not follow the math and I find the logic of it difficult but believe it I will, by faith if nothing else. (sorry, I know, a cheap shot).

However if I understand things correctly, our solar system and our galaxy, both have centres. The view from one location is not the same as from a location very far away.

Now here comes the question, please note I do say question; Is the centre of the universe 'everywhere' because of its size or ? Part of the answer might also touch on the problem (at last for me) that if the various parts all have centres then why doesn't the whole?

Brian

[supernova1965 (Warren)]

I suppose the question is, is the Universe spreading out evenly from the big bang ie, in a circle from the initial point. If this is true then the big bang point of origin would be the center of the Universe

[bojan]

(Geometrical) centre (of something) is defined as a point from which everything else (of that something) is at equal distance... or from which everything (of that something) looks the same.

There is no centre of the universe, because it is the metric of the space-time that expands.

However, if we try to apply the above definition of centre to Universe, then the centre of universe is everywhere.... because Universe looks the same from every point inside it.

[Robh (Rob)]

Brian,

Here's my take on it.
In the "beginning", a singularity came into existence that had no dimensions of space nor time. After the Big Bang and a short period of rapid inflation, space, energy and time were formed. The universe is extremely large and possibly infinite in size. If infinite in size, there can be no centre.
Otherwise, the universe as we see it is not a simple three dimensional environment, whereby if you travel from A to B it is a straight line and the time taken is simply a matter of distance divided by speed. As we look in any direction, we actually look back in time. Eventually, we reach a point close to the Big Bang where no matter has yet formed, no galaxies, no stars. So we are near to the origin of the Big Bang. But this point is in every direction in the sky.

Although our observable universe is fairly flat, we cannot tell if the universe is actually like this on a much larger scale. Our time as we measure it is actually an illusion of a local environment whereby close observers appear to pass time at the same rate. Space inherently contains a dimension of time and on a larger scale time passes at a different rate due to expansion.
Eventually, all objects that are receding at close to the speed of light will seem to freeze in time at what is known as the cosmological event horizon.
In a weird sense then we actually become the centre of our observable universe.

Regards, Rob

[Brian W (Brian)]

Originally Posted by bojan

(Geometrical) centre (of something) is defined as a point from which everything else (of that something) is at equal distance... or from which everything (of that something) looks the same.

There is no centre of the universe, because it is the metric of the space-time that expands.

However, if we try to apply the above definition of centre to Universe, then the centre of universe is everywhere.... because Universe looks the same from every point inside it.

Hi Bojan, there must be something I am missing. I am not saying that I am right with what follows but I do not understand where it is wrong.

According to scientific consensus, to use your words... because universe looks the same from every point inside.

Yet our solar system, at least in the photos sent back from various explorations, looks very different depending upon where you are.

I am tempted to extrapolate from our solar system to our galaxy but that would just be a guess.

But in my mind, if the view of the parts (ie solar systems) change as we move through them we should also see a change in the universe if we were able to move through it at a real fast clip.

Now Bojan if the proof that I am wrong needs serious math to understand it and cannot be explained in English then please just say so and you will get no argument from me.

I just can't seem to get my head around the concept.

Brian

[bojan]

Brian,
If you take into account that 99% (or close to that) of mass of Solar system is concentrated in the Sun (see here) then you can safely say that Solar system looks the same looking from the centre of the system (Sun). The rest (planets) are just statistical dispersion, pretty insignificant for the big picture.
This is the meaning of words "looks the same". You can do some reading on the subject here.

[Brian W (Brian)]

Originally Posted by bojan

Brian,
If you take into account that 99% (or close to that) of mass of Solar system is concentrated in the Sun (see here) then you can safely say that Solar system looks the same looking from the centre of the system (Sun). The rest (planets) are just statistical dispersion, pretty insignificant for the big picture.
This is the meaning of words "looks the same". You can do some reading on the subject here.

Hi Bojan,
I am getting better I actually understood most of the big words. If I am getting the picture 'looks the same' means not an ocular similarity but a similarity in 'physics'. (more or less)

Now the quote below takes us back to my first post...(bold print is mine)

"The cosmological principle is usually stated formally as 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' This amounts to the strongly philosophical statement that the part of the Universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this in a sense says that the Universe is knowable and is playing fair with scientists.[1]"

Does anyone care to put a number to or describe just how large a sufficiently large scale is?

Brian

[bojan]

Much more than local group of galaxies... 1000x + more

[Brian W (Brian)]

Ok then the fact that our solar system changes as we change our location in it is really irrelevant to this discussion cause it is way to small.

We are talking about something like the Hydra - Centaurus Supercluster.

Brian

[Brian W (Brian)]

[QUOTE=Robh;709122]Brian,
Hi Rob, for some reason my earlier response to you got lost?

Here's my take on it...

Although our observable universe is fairly flat, we cannot tell if the universe is actually like this on a much larger scale. Our time as we measure it is actually an illusion of a local environment whereby close observers appear to pass time at the same rate. Space inherently contains a dimension of time and on a larger scale time passes at a different rate due to expansion.
Eventually, all objects that are receding at close to the speed of light will seem to freeze in time at what is known as the cosmological event horizon.
In a weird sense then we actually become the centre of our observable universe.


Rob I actually have no problem with your last statement. I have no problem with the beginning and as you describe it the ending makes sense too.

I just have trouble with this in-between time slot.
Brian

[renormalised (Carl)]

Let's do a little thought experiment here, Brian...try and follow me. Put yourself into the surface of a balloon. Now as it expands when the "big cosmic guy" blows it up (and ignoring where he is because you can't see or even know about him), look out into the space you occupy. What do you see??. Space is expanding away from you in all directions. Now, leave a beacon where you are now and then move a distance "x" away in any direction you care to go within that space. Look around you and also look at the beacon you left behind were you once were. What do you see??. Space moving away from your new position in all directions, including the direction looking towards your beacon.

That is what's meant by the "centre" of expansion is everywhere. Because you and every point in space is moving away from one another due to the expansion of that space. It's not only an expansion of physical dimensions, it's also an expansion in time and that's why it's difficult for some to visualise what's happening. Time, in this case, has to be visualised as an actual physical dimension like length and breadth in order for you to be able to see the results of the expansion.

[Brian W (Brian)]

-

Originally Posted by renormalised

Let's do a little thought experiment here, ---Brian...try and follow me. Put yourself into the surface of a balloon. Now as it expands when the "big cosmic guy" blows it up (and ignoring where he is because you can't see or even know about him),

Ok that's my first problem... I do know about the cosmic big guy. The big guy is the Big Bang and BB is right smack dab in the middle of the balloon.

-look out into the space you occupy. What do you see??. Space is expanding away from you in all directions.

Now for my second problem... Space is indeed expanding away from me but not in all directions. As the balloon expands it brings what is above me closer to me.

-Now, leave a beacon where you are now and then move a distance "x" away in any direction you care to go within that space. Look around you and also look at the beacon you left behind were you once were. What do you see??. Space moving away from your new position in all directions, including the direction looking towards your beacon.

As long as I only think of the surface of the balloon I have no problem. But my mid keeps moving to the interior and to above the surface... sorry I do have a focus problem.

-That is what's meant by the "centre" of expansion is everywhere. Because you and every point in space is moving away from one another due to the expansion of that space. It's not only an expansion of physical dimensions, it's also an expansion in time and that's why it's difficult for some to visualise what's happening. Time, in this case, has to be visualised as an actual physical dimension like length and breadth in order for you to be able to see the results of the expansion.

By an expansion in time do you mean that time itself expands as in a second is of greater duration or do you mean that there is a way to measure the expansion other than by how much space is occupied?

Brian

[renormalised (Carl)]

The latter, Brian. A second is a second, but that space has expanded in time....so that at time A, space was X size. At time B, space was Y size. Space is not occupied....it's space itself which is expanding. It only occupies itself at whatever time you happen to measure it at. At one time it will be smaller than it will be at another.

[Brian W (Brian)]

Originally Posted by renormalised

The latter, Brian. A second is a second, but that space has expanded in time....so that at time A, space was X size. At time B, space was Y size. Space is not occupied....it's space itself which is expanding. It only occupies itself at whatever time you happen to measure it at. At one time it will be smaller than it will be at another.

That I understand.
Brian

[renormalised (Carl)]

That's good to hear...progress

[bartman (Bart)]

Originally Posted by renormalised

Let's do a little thought experiment here, Brian...try and follow me. Put yourself into the surface of a balloon. Now as it expands when the "big cosmic guy" blows it up , look out into the space you occupy. What do you see??. Space is expanding away from you in all directions.

Sorry if this adds any confusion Brian, but Carl, if I am on the surface of the balloon ( attached) when it is inflated and look toward the inside, left, right, up and down - yes I see all expanding away from me. However when I look behind me, wouldn't things get closer to me (if the balloon surface was permeable) or move at the same distance (if the surface of the balloon was solid.)?
Or ... when the balloon is inflated do I detach from the surface? cause then I would understand.
Or am I taking the whole balloon thing too literally?

I've seen this explanation ( the balloon one) before and couldn't work it out.
So thank you Brian for posting this and I hope to understand more as I read more explanations

Cheers
Bartman

[bojan]

Originally Posted by bartman

Sorry if this adds any confusion Brian, but Carl, if I am on the surface of the balloon ( attached) when it is inflated and look toward the inside, left, right, up and down -

Bart, the balloon analogy is valid for 2D space - the surface only. It would be very hard to imagine 4-dimensional balloon expanding in 4th dimension (much better presentation of the expanding Universe) so we are forced to go one dimension lower, to make things simpler or easier to visualise.
So, for your world (as a being on the 2D balloon surface) the "inside " of balloon doesn't exist.. or it is higher, un-observable dimension.

The inflation of the balloon by air pumped inside (do not confuse this with inflation of the Universe) means the balloon surface is increasing and the distances between the points on the balloon surface are therefore increasing as well.

[renormalised (Carl)]

You're being too literal about the balloon analogy

It's only meant to be an approximation representing how the expansion is occurring, not a literal example.

[Brian W (Brian)]

Bartman, my pleasure and don't worry about adding to my confusion I seem to have a never ending capacity for it. Perhaps it is best to remember that with discussions such as this one it is always advisable to suspend some of your disbelief and rationality. The balloon example is for only one part of the picture (at least that is how I view it) and it is possible to push it too far.

Brian


Brian

[avandonk]

Get over it folks. The rest of the Universe does not care.

Bert