Where is the center of the universe?

Genx63

first you say the universe spread out from a single point and then you say that point don't exist. I don't buy the ballon analogy. That would indicate that all matter is spreading out on a 2 dimensional plane. When a star goes supernova does the star all of a sudden not exist? Why is everyone so dead set against a point of origin for the universe? Maybe it's because it would punch too many holes in your theories. I'm no genius I'm not even very smart but even your balloon theory has a center.

minio

Balloon analogy is called analogy because it is not exact description. For start try to imagine that balloon has 3D surface and its expadnig in 4D space.

Spourk

Do a google search for Hypersphere. You're not quite grasping the balloon analogy the way it's meant to be presented, if you are still trying to say there is a center of the balloon. A hypersphere is a little easier to look at and see how you can actually travel and never reach a center, or an edge, it just keeps looping back on itself in higher dimensions.

Try this thought experiment: If you were 1 dimensional, and lived on the outside of a circumfrence of a circle, where would the center be? As a 1 dimensional being, you can only traverse the line on the outside of the circle, you'd never be able to reach the "Center" because that is in the 2nd dimension. You could go forward, or back, nothing else. Where is the center?

That being said, how well did the "Earth is the center of the universe" theory work out for Cosmology?

(Forgive me if this has all been presented to the OP already)

Drakkith

Of course. That's why it's and analogy. Extrapolating the same principles into 3 dimensions instead of two would give us a hypersphere. Currently the standard model doesn't care whether we are on an actual hypershpere or not, it simply says the universe is expanding.

The material that made up the star still exists. Whether you could call it a star or not is debateable.

You are correct. A point of origin for the universe would be a big glaring hole in our current model of the universe. A model which is the best fit to observations and theoretical work by far. Punching holes in the theory is akin to not believing gravity exists and saying that fairies hold everything together. You would have to make up stuff that isn't even observable in both cases.

It isn't a theory, it's an analogy. A way to visualize and a tool to help people understand the basic concepts. Don't take it for more than it is. Arguing against it is like arguing that students shouldn't start learning physics with blocks sliding on frictionless surfaces because they don't exist. They do that because it's easier to learn the basics that way.

ynot1

Yes the observable universe becomes bigger. Point being you can observe more with better telescopes. Why would the universe get bigger, except for expansion?

Drakkith

The observable universe wouldn't increase in diameter no matter how many telescopes we built or how big we built them. We simply can't see past a certain point because there isn't anything to see.

ynot1

Certainly. I should have said the observed universe. Maybe a distinction without a difference?

ynot1

I can define the center of a circle - every point on the circle is equidistant from the center - pick the closest one. I presume such can be said of a sphere except you only have one choice. But there is no point equidistant from every point on the surface of the earth, as well as the universe, ergo the earth and the universe technically have no center according to my understanding of the definition of center. This assumes the universe has a surface, but that is debatable.

Drakkith

Certainly as we get more telescopes and they get bigger and better we will be able to see dimmer objects or get better resolution, but I wouldn't say the observed universe becomes "bigger". But I'm not one of those philosophers you were talking about either.

ynot1

I meant the telescopes get bigger, not the universe.

phinds

So, you figure that when folks learned how to sail around the world, and could therefore see more of it, it got bigger?

I think you misunderstand the term "observable universe". It is NOT based on what we CAN see, it is based on what we COULD see, and it is at present 13.72billion light years in radius and if we had the most amazingly wonderful telescopes that could possibly be built, and that could see throughout the electormagnitic spectrum, it would STILL be 13.72 light years in radius.

Fredrik

That's the number of years that the oldest light has been traveling towards us, but due to the expansion of the universe, the actual radius in significantly larger. I don't remember exactly, but I think it's about 45 billion light-years.

phinds

Yes, I agree, and I knew that but got sidetracked by the silliness of the concept of the OU getting bigger because of telescopes so I fixated on the photon age, not the current diameter (which of course IS getting bigger, but not because we have better telescopes)

ynot1

So our telescopes only show us the universe in its past. Wouldn't it be nice if we could see the present? In fact we're building them right now - the gravitational interferometers. But you say even gravitational waves take time to propagate, so we really couldn't see the present even if we wanted to. Yes unfortunately this planet is being accelerated so we can't see anything in the present. However we sure could see a lot more considering all matter created during inflation is now in gravitational communication since the universe was very small at that time. The trick is when objects accelerate the changes in their gravitational fields propagate only at the speed of light. However note static gravitational fields are in instantaneous gravitational communication.

Cosmo Novice

Yes it would be nice if we could see the present but unfortunately we cant, the Universe speed limit forbids it. There is no such thing as instant gravitational communication on a static field, this is more to do with observation than instantaneous propogation, in fact gravity propogates at the speed of light.

Please see a relevant wiki extract:

The consequence of this, is that static fields (either electric or gravitational) always point directly to the actual position of the bodies that they are connected to, without any delay that is due to any "signal" traveling (or propagating) from the charge, over a distance to an observer. This remains true if the charged bodies and their observers are made to "move" (or not), by simply changing reference frames. This fact sometimes causes confusion about the "speed" of such static fields, which sometimes appear to change infinitely quickly when the changes in the field are mere artifacts of the motion of the observer, or of observation.

In such cases, nothing actually changes infinitely quickly, save the point of view of an observer of the field. For example, when an observer begins to move with respect to a static field that already extends over light years, it appears as though "immediately" the entire field, along with its source, has begun moving at the speed of the observer. This, of course, includes the extended parts of the field. However, this "change" in the apparent behavior of the field source, along with its distant field, does not represent any sort of propagation that is faster than light.

ynot1

Good quote. Note static gravitational fields do not propagate.

Drakkith

True, but a static field permits no communication either.