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What is at the center of the universe? after the Big bang?
I believe Balloon and ant example is a poor analogy. In this analogy, ant would see only other ants moving away in two dimensional space. But in actual universe, you would see matter moving away in three dimensional.
The earth! We can't see that now, because, I believe, the universe is in a temporary state, so it is not now obvious.What is at the center of the universe? after the Big bang?
If there is no center, all the galaxies would be attracted equally by the surrounding galaxies. So there won't be any net gravitational effect on any Galaxy on a large scale (Ignoring short distance ones like Andromeda). But still
most of the astronomers believe in a big crunch due to gravitational attaction provided the matter density in the universe is less than critical density and also Dark energy is said to be of overcoming gravity. So here we are clearly accepting gravity on large scales which is not possible if the universe doesn't has a center.
I am not saying that there is a center to a universe but still its not clear.
there is no centre, or you can say everything is at the centre.. Because the universe began in a single point, the whole universe and its centre where the same point, so now everything is at the centre of the universe.
This is also why no matter where in the universe you place yourself every thing seems to be moving away from you, like you were at the centre. Because of the expansion of the universe...
Does that mean that the Universe is constant? Does that mean while the outer shell is expanding ... the Universe is also contracting at the center?
Also, Isn't ther violation of conservation of mass during Big bang?
Sorry but this is all wrong. The solution to the equations of general relativity describing a homogeneous, isotropic and infinite are perfectly happy with the current observations. You do not need to have a center of the universe that everything else is moving away from. There is no net gravitational force on anything in the universe, since in general relativity gravity is not a force. Instead all the matter in the universe follows geo-desic paths determined by solving the equations. The solutions tell us that everything moves apart even though the infinite universe is homogeneous.
It all boils down to initial conditions. The Big Bang caused everything to begin moving apart and hence they continue to do so. It is a common misconception that the Big Bang happened at a point. This is not the case. It happened everywhere. There is no one point you can trace all the matter in the universe back to if you run time backwards.
By the way, the Big Crunch is not thought by anyone to be a reasonable prediction of the universes future. It is not supported by the observations at present. Even if it was, it dosn't require a center of the Universe to exist in order to occur. A Big Crunch is NOT where all the material in the Universe moves to a single point. What it is is that density of the universe goes to infinity, but there can still be an infinite (or indeed finite) distance between points in the infinitely dense universe.
I wouldn't argue with general theory of relativity. Here you are considering universe as infinite. So many things are possible under infinite universe. If the universe is infinite, no one would dare to say that there is a center to the universe. But how can anyone be so sure that universe is infinite ? and not finite ?. Is there any sound practical evidence that universe is infinite ? Infinite universe would also mean infinite energy which is beyond my grasp. Please explain.
You are saying that Big Bang happened everywhere. How can this be ?
Can you give brief explanation or direct me to some link ? I never heard of this..
You are saying that under big crunch, density of the universe goes to infinity.
We know that there is nothing higher than infinity. How one can measure distances in an infinitely dense universe ? Please explain.
Infinite density means zero volume.
How can one measure distances in zero volume ? Are you talking about extra dimensions ?
Those questions are irrelevant, since the universe does not need to be spatially infinite to lack a center. That's one of the things that the balloon analogy tells us.So many things are possible under infinite universe. If the universe is infinite, no one would dare to say that there is a center to the universe. But how can anyone be so sure that universe is infinite ? and not finite ?.
The Big Bang was not an explosion and the universe looks pretty much the same in every direction.Whats at the center, well, first answer whether universe in restricted to some expanse or not ? The point of bigbang needn't be the center (how do we know if the explosion was symmetrical in all dimensions)
PS: Sorry if this sounds unconvincing,i am a novice in this field. I am just sharing my views.
Those questions are irrelevant, since the universe does not need to be spatially infinite to lack a center. That's one of the things that the balloon analogy tells us.
"It is a common misconception that the Big Bang happened at a point. This is not the case. It happened everywhere. There is no one point you can trace all the matter in the universe back to if you run time backwards."
"You are saying that Big Bang happened everywhere. How can this be ?
Can you give brief explanation or direct me to some link ? I never heard of this.."
Visualizing it isn't really possible because our eyes (and thus our brains) are limited to seeing in 3 dimensions, but in 1 dimension (the edge of a circle), the perimeter has no center, but finite length and is curved in a second dimension. In two dimensions (the surface of a sphere), the surface has no center, but a finite area and is curved over a third dimension. In three dimensions, then, the space would have no center but finite volume and there must be a curvature in higher dimensions. The three concepts are the same.
You can't visualize why/how, but if you fly far enough in one direction, you'll end up back where you started, just like if you were flying around the earth.
All the above looks fine but is there any evidence for fourth dimension which is beyond human perception ?
How can you be so sure that if someone travels in some direction in the universe would reach the same starting point ?
Those questions are irrelevant, since the universe does not need to be spatially infinite to lack a center. That's one of the things that the balloon analogy tells us.
Our space-time manifold is already four dimensional. It can be embedded in a single space of some higher dimensionality, but this fact is usually regarded as mathematical trivia rather than something physically meaningfull.
Some people confuse the "local observable area" of the universe, with the entire thing (As I did until recently). This makes the Earth appear as the center.
The Big Bang was not an explosion and the universe looks pretty much the same in every direction.
Talksabcd,
The evidence for a 4th dimension is gravity and time dialation(though there may be more to it that we are unable to observe.
Maxwells Demon,
I'm sorry the last part of my post was so vague. We are in agreement. My point was that an observer on Earth sees everything moving away from him and if he disregards the background radiation, the fact that space and time began with the "Big Bang", and the observations from other places, it would be natural for him to think that he was in the center. Even though this is incorrect.
If there was a center of the universe, then we would find the cosmic background radiation stronger in one direction than another. This is not the case. While NASA's COBE satelite found variations, that is believed to be the beginning of the first structures in the universe, it found the background radiation to be the same in all directions.
The phrase "BIG BANG" leads one to think of the expansion of the universe as an explosion. This is incorrect. An analogy I use is to consider the universe as a loaf of raisinbread expanding as it cooks. The raisins being the galaxies. An observer on one raisin sees all the other raisins moving away. While an observer on a distant raisin sees the same thing. This analogy is 3 dimensional and the universe is expanding in 4 dimensions. This is why it is so difficult for our minds to comprehend.
Some people confuse the "local observable area" of the universe, with the entire thing (As I did until recently). This makes the Earth appear as the center.
If the cosmic background is same in all directions then it doesn't mean that
there is no center to the universe. We see the cosmic background from the
point of last scaterring. If the point of last scaterring is within the finite universe then we should see homogenous cosmic background in all directions irrespective of whether there is a center to the universe or not.
We are not talking abt Time as fouth dimension but abt spatial fourth dimension. Is there any evidence for a spatial fouth dimension ?