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"mikesithole48 asked the Naked Scientists: Is the universe finite or infinite and did it hve a beginning? Plus I'd love to understand about dark energy.What do you think?

paper Draw a large circle this is your FINITE boundary

Dark energy , dark matter, dark anything is basically "dark" because we cannot understand it.

Dark energies and matter are forces added to universal equations to fix the fact that our observable universe is 99.99999% "EMPTY" Space.

oh yeah? 8D

You can do this to infinity

Quote from: njskywalkerYou can do this to infinityThis is not a criticism of the point you were making, this use of the term infinity is very common. My own feeling is that unbounded is less confusing than infinite, because there is no way in which infinity can be reached, even in theory.Pete may well shoot this down, but I see no way in which something that is finite can become infinite.

any finite area has infinite points of information embedded in itself.

Call the distance between me and the finish line L. Let K = 1/L. Then when I reach the finish line K is infinite whereas it started out finite.

I would not be so rash as to argue with the maths, Pete, but can you show me a physical example of any finite object that can actually become infinite?

If the Universe is finite, but expanding, it might expand for ever, but will it reach a point where one can say: "it is now infinite"?

Quote from: njskywalkerany finite area has infinite points of information embedded in itself. Where in the world do you come up with this stuff? If you were tying to say that a point has information in it then you're wrong. Otherwise what information are you talking about tht pertains to this problem?

Quote from: Pmb on 24/07/2013 20:44:18Quote from: njskywalkerany finite area has infinite points of information embedded in itself. Where in the world do you come up with this stuff? If you were tying to say that a point has information in it then you're wrong. Otherwise what information are you talking about tht pertains to this problem?if you have enough space between yourself and the earth the earth will appear as a POINT. As you go closer that 'point' shifts into many 'points'. A grain of sand appears in this dimension as a point. Same principle applies zoom into that sand grain and billions of more points emerge . ALL can thought of as INFORMATION. Infinity exist in every point.

No i wasn't.

Pete, but can you show me a physical example of any finite object that can actually become infinite?

If the universe started out as being zero in size and now has a flat spatial geometry (and observations are consistent with this) then the size went from finite (zero) to infinite.

In fact the term infinite quite literally means without bound or something similar

Have you ever considered the energy in the field of a point charge like an electron. The energy is actually infinite!! The charge density is quite literally a Dirac delta function. That means it has infinite charge density where the electron is located. This is a famous and I believe unresolved problem in quantum theory.

In the hope that you didn’t really mean that you “hold against people [is] their inability to understand…” I shall press on.

"mikesithole48 asked the Naked Scientists: Is the universe finite or infinite and did it have a beginning? Plus I'd love to understand about dark energy.

How can the Universe be infinite if it was all concentrated into a point at the Big Bang? ... ...The Universe was not concentrated into a point at the time of the Big Bang. But the observable Universe was concentrated into a point. The distinction between the whole Universe and the part of it that we can see is important.

Another chance to wheel-out this old link

“I don’t care what your math says. In my opinion the result is not what every scientist or mathematician thinks it is.”

It does suggest that time and space, as well as galaxies, existed before the Big Bang.

It also says that the BB did not trigger the expansion of the our Universe, so there seem to be some assumptions that may not readily be verifiable.

Quote from: Bill S on 28/07/2013 16:47:33It does suggest that time and space, as well as galaxies, existed before the Big Bang. I sort of understood it has saying… If every point in an infinite universe is the centre of its own observable universe, then running the infinite model backwards results in a singularity at every point, in other words, an infinite expanse in a state of singularity. Correct me someone…singularity is a state not a point??That is to say, we can’t understand the spacetime and physics when it’s in a state of singularity. Winging it now… Our present understanding of spacetime and physics pops into existence with the big bang.

The context in which you use singularity matters. Technically, it's a point where equations break down such that your mathematical quantity becomes undefined.

we can’t understand the spacetime and physics when it’s in a state of singularity. ... what happens to spacetime in a state of singularity is beyond current physics... I think.

It's not a true function and one reason for this is that, like the concept of infinity, defining a distribution this way is done in terms of limiting processes.

I was under the impression that if the universe was finite in size (even at the big bang) it would still have to be infinite in size, and if it was infinite in size at the moment of the big bang, it would still be infinite in size.

The big bang is generally called a singularity ...

If there were an instant, at a "big bang," when our universe started expanding, it is not in our cosmology as now accepted, because no one has thought of a way to adduce objective physical evidence that such an event really happened.

Quote from: JP I was under the impression that if the universe was finite in size (even at the big bang) it would still have to be infinite in size, and if it was infinite in size at the moment of the big bang, it would still be infinite in size.Assuming your first "infinite" should have been "finite"; this is a major part of the line of reasoning I have been trying to follow. Namely that (physical) things that are finite, remain finite, and those that are infinite, remain infinite. For a few ecstatic moments I thought Pete agreed with me, but then his “Although I said no at first I'd like to change my mind” dashed my euphoria. Hopefully he will address your “impression”.

Quote from: JPThe big bang is generally called a singularity ...Were you aware that there is no event in the big bang which is actually called "the big bang"?From Principles of Physical Cosmology by P.J.E. Peebles, Princeton University Press, 1993, page 6QuoteIf there were an instant, at a "big bang," when our universe started expanding, it is not in our cosmology as now accepted, because no one has thought of a way to adduce objective physical evidence that such an event really happened.

If there's a good reason why taking that limit doesn't work, I'd love to learn more.

I'd be interested to know what cosmology says as you take the limit T->0, where T is the age of the universe. Does it predict an infinitely dense state we could tall "the big bang"? (This is almost certainly non-physical, but does GR predict it?) I've been led by pop-sci to believe that it does predict this "infinite density." But my biggest question, stated above, is whether a bounded universe could become unbounded or if bounded must remain bounded for all time and unbounded must remain unbounded for all time. This ties into Bill's question on whether a finite universe can become infinite.

Pete gave the example of 1/(distance remaining) as you move between two points becoming infinite. Ligharrow gave the example of a series with infinite terms that sums to a finite number.

Ah yes, that should have been "infinite."

QuotePete gave the example of 1/(distance remaining) as you move between two points becoming infinite. Ligharrow gave the example of a series with infinite terms that sums to a finite number.Absolutely right, undoubtedly mathematically sound, but has anyone adduced “objective physical evidence that such an event really happened”?