Possibly, but the question is certainly not settled.
It's not possible to have an expanding Universe if the Universe is infinite
Oh yes it is In fact, the classic big bang cosmology, before all this accelerating expansion confusion was known, had three classic variants, two of which were infinite.
It's not possible to have an expanding Universe if the Universe is infinite - the concept of relative size requires discrete quantities.
This is wrong, expansion is not about size it's about the distance between points.
As a simple mathematical analogy consider the function f(x) = 1.5x, evaluated across the real entire number line. If you take any two point on the line, they end up further apart after the transformation, yet the space convered by the output is the same infinite size as the original space.
This thread is not about what came before the Big Bang, and it is not about atheism, and it is not about cause and effect, and it is not about God. These are all valid topics for discussion, but please raise them in threads where they would be on-topic.
Bare links with no supporting discussion should be avoided. Make the argument in your own words and use links as supporting references.
In other words, even if your video were on-topic, you should still use it only as a supporting reference, not as your entire argument.
I'm participating in this thread under my Percy alias, but I am not going to recuse myself from further discussion just because of a single hand grenade lobbed in by someone who's been absent for over six months.
It's a deep and complex topic so really deserves a thread of its own. Why not propose one, and I'll join in. I was thinking of starting a thread on 'what is matter and energy?', but that may well be best placed in your thread.
BTW, this thread is about what came out of the Big Bang, not what may or may not have gone into it
I agree with cavediver. Can you propose a smart thread please? What I mean is, do show the video, it's delightful. But also summarize what seem to be the best arguments from it in your own words, so that people have things to argue for and against and build their own posts out of.
The brilliant posts this current thread is acting as a vehicle for need to be somewhere with a less shallow beginning than Why is stuff round?
If I understand Son Goku correctly, he's talking about the observable universe.
I asked the question because I would think physicists would say 'visible universe' when they wanted to talk about the visible universe, and univers when they wanted to refer to the universe. Hence my question, if the universe is supposedly Euclidian (therefore infinite), then how can you measure it's size ?
Actually as a physicist I usually use the phrase "our universe" or even "the universe" for the observable universe. The actual entire universe is usually called spacetime or the "present hypersurface". This is confusing on my part though, so I've changed the post to be less confusing, using observable universe instead.
slevesque writes:
if the universe is supposedly Euclidian (therefore infinite), then how can you measure it's size ?
Well, there is nothing to say that the universe is definitely infinite. Recent WMAP measurements show that space is essentially flat (Euclidean). However this is just consistent with it being infinite, we'd need something more solid to make the conclusion of it being infinite more solid.
How does an infinite universe fit with the big bang? I mean, if it could be condensed into an infintisamely small point, then grew larger, it certainly wasn't infinite, right?
I hunt for the truth
I am the one Orgasmatron, the outstretched grasping hand My image is of agony, my servants rape the land Obsequious and arrogant, clandestine and vain Two thousand years of misery, of torture in my name Hypocrisy made paramount, paranoia the law My name is called religion, sadistic, sacred whore. -Lyrics by Lemmy Kilmister of Motorhead
In the Big Bang model, if the universe is infinitely large now it was infinitely large in the past. The expansion means that any "piece of space" that was some size 10^(-36) seconds after the Big Bang, is now vastly larger.
Huntard writes:
if it could be condensed into an infintisamely small point
General Relativity breaks down at this point. The infinitesimally small singularity is an artefact of General Relativity being no longer applicable. In truth we can trust General Relativity up to a certain point in time, at which point it says that any given region of the universe today was extremely small. Going beyond this, back to the time when General Relativity predicts everything being infinitely small, is trusting the model beyond its own limits.
An analogy can be found in some models of ice. There are statistical mechanical models of ice, that describe ice very well up to about 0 degrees. The models predict that ice becomes more and more brittle as you increase the temperature. However they predict that ice becomes infinitely brittle at 0 degrees. Of course this is incorrect, what really happens is that ice becomes water at 0 degrees. Just like General Relativity the model works perfectly fine up until it develops a singularity (in this case infinite brittleness), to go further you need to add new details. In the case of the ice models, you need to make the model less simplistic and add more properties of water to it. In the case of General Relativity, we don't know.
In the Big Bang model, if the universe is infinitely large now it was infinitely large in the past.
Yes, that's what I figured. My understanding however was that the big bang model meant that it couldn't have been infinite.
The expansion means that any "piece of space" that was some size 10^(-36) seconds after the Big Bang, is now vastly larger.
Yes. Infinite spacetime can expand, like the hotel with the infinite rooms and infinite guests that fits one more guest in there. Infinities aren't a set number.
General Relativity breaks down at this point. The infinitesimally small singularity is an artefact of General Relativity being no longer applicable. In truth we can trust General Relativity up to a certain point in time, at which point it says that any given region of the universe today was extremely small.
Can something being extremely small be infinite? It's more a case of coordindates and their proximity to eachother, relative to today, isn't it?
Going beyond this, back to the time when General Relativity predicts everything being infinitely small, is trusting the model beyond its own limits.
Well yes. If it can't tell us anything about something, then I guess it is stupid to expect it to be accurate about it.
However they predict that ice becomes infinitely brittle at 0 degrees. Of course this is incorrect, what really happens is that ice becomes water at 0 degrees.
Would that not infact constitute infinite brittleness, being liquid and all (or am I misunderstanding brittleness)? Or does even liquid have something "solid" to it? (I know about molecules and stuff, but can we really call them "solid")?
I hunt for the truth
I am the one Orgasmatron, the outstretched grasping hand My image is of agony, my servants rape the land Obsequious and arrogant, clandestine and vain Two thousand years of misery, of torture in my name Hypocrisy made paramount, paranoia the law My name is called religion, sadistic, sacred whore. -Lyrics by Lemmy Kilmister of Motorhead
are you saying that in your opinion, matter is a field and that means that matter is not also stored energy(defies college text books)? Whatever the case, matter is definitely stored energy(dormant) that can be excited. E=MC(Einstein, 1879-1955). The "metal spring" in your example is a good example here. A depressed "metal spring" has a potential amount of energy stored and it takes a certain KEY to release that stored energy(chemically or in the depressed metal spring). Just like it takes a special KEY(stimulus) to open a locked storage compartment. The energy in matter is simply locked up/rendered or dormant and requires a key(stimulus) to release it. Another example is a plant. Plants absorb energy all day long from the sun and that energy is released when digested via the key/stimulus of enzymes in the digester(a stimulus). FYI: Energy is in a constant state of conversion. These conversions typically require a KEY(a stimulus) for the conversion to take place.
Thanks Sasuke
Edited by Sasuke, : format edit and additional context
everything in our universe is done via chemical reactions(Nivaldo J Trio, Introductory Chemistry 3rd edition, 2009). The plant in my last post is a good example. Plants absorb energy from the sun and eventually are digested by human beings in order to harness the stored energy that is dormant. Just like Einstein preached even, E=mc^2.
The depressed metal spring in your example, The depression of the metal spring requires energy to do it, well the energy that is depressing that metal spring also requires a stimulus to depress the metal spring. The stimulus that causes the compressor to depress the metal spring also requires another stimulus and this cycle never ends. Energy is in a constant state of conversion. If matter is not stored energy, are plants not made of matter? and if plants are made of matter, why do we eat them?
Thanks Sasuke
FYI: You should follow standardized lessons in your classes as to avoid providing less accurate data.
In fact, the classic big bang cosmology, before all this accelerating expansion confusion was known, had three classic variants, two of which were infinite.
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