The discussion centers on the misconception that the universe, as described by the Big Bang theory, is expanding into something. Participants clarify that the Big Bang represents an expansion of space itself, not an explosion into pre-existing space. The universe is a four-dimensional spacetime geometry without edges, and its expansion is characterized by galaxies moving away from each other. Key insights include the distinction between local and cosmological energy conservation, and the acknowledgment that the Big Bang singularity does not conform to traditional cause-and-effect reasoning.
PREREQUISITESStudents of cosmology, physicists, and anyone interested in understanding the nature of the universe and the Big Bang theory.
No, there doesn't. As @Vanadium 50 says, the Big Bang model does not say this.jwaldo said:there has to be something (or really nothing) there for the universe to be expanding into.
Doesn’t it make sense though? If you take a firecracker and compress it on all sides it will not blow up but if there is something for it to explode into it will explode and expand.PeterDonis said:No, there doesn't. As @Vanadium 50 says, the Big Bang model does not say this.
I am simply saying there has to have been something to the Big Bang to explode intoIbix said:The universe is not a finite region expanding into a larger region. It is literally everything there is. We describe it as expanding because the things we can see in it are all getting further apart in a "centerless" way - which is to say that wherever you are in the universe, distant galaxies are all moving away from you with a speed that increases with distance. It is not because we can see the whole thing and can see its edges moving away - indeed it doesn't have edges as far as we're aware.
No, there doesn't. You are thinking of the Big Bang as an explosion from a point in space. That model is not consistent with the universe we see. The Big Bang happened everywhere at once, and the initial "explosion" is the start of spacetime as a thing. It doesn't need a pre-existing background to work with.jwaldo said:I am simply saying there has to have been something to the Big Bang to explode into
Not if you actually understand the Big Bang model, no.jwaldo said:Doesn’t it make sense though?
The Big Bang is nothing like a firecracker, or any ordinary explosion.jwaldo said:If you take a firecracker
Just a general note, reasoning from analogy is extremely dangerous. You really need to understand where your analogy differs from whatever you are analogising, and that's what's biting you here. A firecracker is very little like the Big Bang. I wouldn't even call the Big Bang an explosion if I could think of a less inappropriate word. There was no pile of explosives sitting there waiting to go off. There was no place where it all started - it started everywhere.jwaldo said:If you take a firecracker
The universe is not a fire cracker. It's a four dimensional spacetime geometry.jwaldo said:Doesn’t it make sense though? If you take a firecracker and compress it on all sides it will not blow up but if there is something for it to explode into it will explode and expand.
Are you asking us or telling us?jwaldo said:I am simply saying
Only if you refuse to learn any actual physics.jwaldo said:Doesn’t it make sense though?
But, we know something can't happen in its own. There need to be something to cause the big bang. And also energy can neither be created nor be destroyed. So the energy released in the big bang had some forms before the big bang. So where or in what form these vast amount of energy exist if there was nothing before big bang. In other words what is energy..? From where or how energy came for the first time in the universe..? These are just my thoughts. Apologizes if there is any mistakes in it.Ibix said:No, there doesn't. You are thinking of the Big Bang as an explosion from a point in space. That model is not consistent with the universe we see. The Big Bang happened everywhere at once, and the initial "explosion" is the start of spacetime as a thing. It doesn't need a pre-existing background to work with.
Just so you know, that statement is only true locally. It does not hold for cosmological distances. Light that is emitted with a certain amount of energy has less energy if/when it arrives at a cosmologically receding detector. Some of its energy has just disappeared due to accelerating cosmological expansion.Junak said:And also energy can neither be created nor be destroyed.
it’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920’s: energy is not conserved in general relativity.
Junak said:There need to be something to cause the big bang.
No. We don't.Junak said:But, we know something can't happen in its own
No, we do not know this. Some models (such as eternal inflation) have events extending infinitely far back into the past; others do not. All of the models are consistent with our best current understanding of physical laws.Junak said:we know something can't happen in its own. There need to be something to cause the big bang.
This is a property of the Einstein Field Equation, yes. And the EFE applies at every event in the spacetime manifold. But the Big Bang initial singularity (in models where there is one) is not part of the spacetime manifold, and the EFE is not well-defined there. (A more detailed discussion of this point would go well beyond the "B" level.) So this property of the EFE cannot be used to argue the point you are trying to argue.Junak said:energy can neither be created nor be destroyed.
No we don't.Junak said:But, we know something can't happen in its own
This is not true in general. There are local conservation laws in general relativity, so it does predict that you can't get free energy schemes. But you can only define a global conservation law in some spacetimes, and cosmological spacetimes are not of that type. So energy conservation isn't a particularly plausible argument in terms of origin of the universe.Junak said:And also energy can neither be created nor be destroyed.
You're assuming global conservation of energy. You are also assuming that "before" makes sense when you are talking about something that is not part of spacetime, but "before" is a notion about events in spacetime. You first need to justify using those concepts (i.e., come up with a good mathematical framework that includes them, make predictions with it and show that those predictions are consistent with at least some experimental data) before you can take the question seriously.Junak said:So where or in what form these vast amount of energy exist if there was nothing before big bang.
I hope the OP, @Junak , has read the linked article. I never studied cosmology, but I have read a few popular articles and books. These left me with questions and ideas similar to @Junak 's. The Sci Am article does a pretty good job addressing these questions.diogenesNY said:This might be a good starting point. An article by Charles Lineweaver and Tamara Davis entitled Misconceptions about the Big Bang. This is an article originally published in _Scientific American_ magazine by two astonishingly credible researchers who have managed to pack a whole lot of science into a very readable article.
https://www.scientificamerican.com/article/misconceptions-about-the-2005-03/
If you have paywall problems, here is another, albeit differently formatted version:
https://ia904500.us.archive.org/35/items/lineweaver-davis-inflation-expansion/LINEWEAVER DAVIS INFLATION EXPANSION ++++ .pdf
Okay, maybe this is even the best one, with the original SciAm illustrations and pagination:
http://pages.erau.edu/~reynodb2/LineweaverDavis_BigBang_SciAm_March05p36.pdf
Hope this helps and is the beginning of a fun intellectual adventure for you.