If energy cannot be created or destroyed, doesn't the universe exist forever?
According to the first law of thermodynamics - the conservation of energy law - it cannot be created nor destroyed but can change from one form to another. If this is the case can we really ascribe the concept of "a beginning" and "end" to the universe? We reason that it must have a point of origin because energy has the behaviour of spreading out and increasing energy thus at one point it must have been all "together" in one singularity. But that assumes that a quality of energy isnt that it disperses towards a point of potential to once again spread out which is identical (in the end) as it was in the beginning. Also... who's not to say black holes are the reverse collector or gatherer of energy in the form of matter and that eventually all black holes combine together back into the very same singularity that began everything. Thoughts?
Comments (16)
I watched this youtube vid recently. You might like it.
https://www.youtube.com/watch?v=uD4izuDMUQA
Yes, scientists don't say that the universe was "created" at the Big Bang, but it is commonly said that matter can't be created or destroyed, which is the only context I see Benj96 using the term.
This.
Conservation of energy is, per Noether's Theorem, a consequence of time translation symmetry. At cosmological scales time translation symmetry breaks down and, as a consequence, so does energy conservation. I won't speculate much more than this... but here's a good explanation from Nick Lucid of science asylum:
https://www.youtube.com/watch?v=cnGYMe6GBeQ
Only holds for closed systems. If you consider the Earth apart from the sun, it gains energy constantly. If you put the sun back in, the sum of energy asset and liability goes to zero.
Oh. Thanks for the info. I just remembered something. Many top-notch scientists have publicly confessed about their complete bafflement regarding the question: why the universe was in a low entropy state at the beginning? Do you think this has anything to do with the OP? In my humble opinion, the universe's "creation" for a scientist is not that matter and energy were brought into existence at the Big Bang but is actually the evolution of a system from low entropy to high entropy.
Another way science can be consistent about this is to admit that neither energy nor matter has been created or destroyed in the sense that all energy-matter in our current universe is no more and no less than that contained in the Big Bang singularity but the universe doesn't refer to this total energy-matter but rather to the configuration of energy-matter that is new - different from the Big Bang singularity - and so was created.
It's something like jigsaw puzzle - there are as many pieces in the beginning (before the puzzle is solved) as there are in the end (after the puzzle is solved) - mass-energy conversation - but the configuration of the pieces is new and thus can be thought of as created.
My largest uncertainty is not understanding what space-time is. If I think about it, it rather sounds like we are describing trajectories. Space... doesn't seem to exist. Does it? What is space? It's simply a dimension as far as I can tell (ie distance, relationship etc). Time is a measure of change. Time depends on matter, in a sense so does space. So wouldn't space-time just be a measure of change in the trajectories of objects?
If we had an infinite space with no matter at all, we couldn't describe that as a "space" (ie there are no dimensions). With no spatial or temporal dimensions, it isn't anything at all, yet it would be infinite. Which suggests that the energy available is infinite, yet unmeasurable until matter exists (after which the dimensions of time and space also exist and can be measured).
So the void or the energy potential is sort of effectively infinite in both dimensions but a universe only exists while there is matter. So the answer to the question is that there is a beginning and an end to the universe, but the energy potential remains infinite.
Does that make any sense?
Time is often defined as change but this is a weak definition; change is evidence of time but not a definition of it. (Space)time is a geometry according to which change happens. That is, time is the way change happens; it is the order according to which change happens. In physical spacetime general relativity describes how change happens. G.R. describes the geometry of time and how things happen in it. That geometry is time.
At the end, during the Q&A period I asked how it was that the universe had such a low entropy value. The professor's response??
"When God created the universe he created the Second Law of Thermodynamics"
The whole class laughed.
Just for the record, I have no religious beliefs. And I also was - and still am - a very mediocre Physicist.
Intesting, I think change is a fine definition of time.
It breaks down in the sense that in a dynamic, curved and possibly infinite spacetime there is no uniquely correct way of calculating and keeping track of the total energy. Physicists don't seem to be much bothered by that though, because energy is mostly useful as a budget in local transactions.
Quoting EricH
Wha...? What was on the curriculum?
Quoting EricH
Well, that's a crap answer and not even a good joke. The past hypothesis, as the (supposedly) low initial entropy of the universe is known (after David Albert), is an interesting and contentious issue.
Hard to re-collect - that was 50 years ago. For whatever reason, even tho I was a physics major, it was a liberal arts degree - I took Philosophy 101/2, World History, French Literature, Art History, etc.
Quoting SophistiCat
It was funny at the time. Guess you had to be there . . . . . .