# Is my reasoning correct? Energy "before" the big bang?

It seems as though that according to conservation of energy, there could never have been a point in the timeline of the universe where nothingness existed. It seems to me that the claim that there was nothingness before the big bang would violate these laws. For example if E is the total energy of the universe then the law states that E = constant. If E1 is the total energy of the universe at an arbitrary time t1 and E2 is the total energy of the universe at arbitrary time t2 , then E1 = E2. lets say t1 is before the big bang and t2 is right now. If there was nothingness before the big bang, then E1 = 0. Since right now it is obvious that E2 > 0 , or , E2 != 0, then E1 != E2 which would violate conservation of energy. Is this line of reasoning correct? if not, why?

mfb
Mentor
Without a universe, there is no conservation law a big bang could violate. "Before the big bang" is meaningless if the universe started with it, and you cannot assign an energy to something that does not exist.

By the way: general relativity does not have global energy conservation.

jfizzix
Gold Member
Conservation of energy arises due to the time translation symmetry of the laws of physics (see Noether's theorem).

Our current theories say that there is effectively no time before the Big Bang (in the geometric sense that one cannot go further north than the North Pole). If that's true, then one simply cannot translate from the Big Bang further into the past and say the laws of physics remain invariant.

If there is no time translation symmetry at the point of the Big Bang, there is likely no conservation of energy (as we know it) either.

At least currently, we can only speculate about what the laws of physics were like before the big bang (if there even was a "before").

jfizzix
Gold Member
By the way: general relativity does not have global energy conservation.
Is that not what "dark energy" and the "cosmological constant" is for?

Time translation symmetry is certainly a tricky thing in general relativity, but is there really no workaround?

mfb
Mentor
Is that not what "dark energy" and the "cosmological constant" is for?
No. There is no unique meaningful way to define "the energy of the universe at a specific point in time", and as far as I know no matter how you define it there is a process that could change it.

It seems as though that according to conservation of energy, there could never have been a point in the timeline of the universe where nothingness existed. It seems to me that the claim that there was nothingness before the big bang would violate these laws. For example if E is the total energy of the universe then the law states that E = constant. If E1 is the total energy of the universe at an arbitrary time t1 and E2 is the total energy of the universe at arbitrary time t2 , then E1 = E2. lets say t1 is before the big bang and t2 is right now. If there was nothingness before the big bang, then E1 = 0. Since right now it is obvious that E2 > 0 , or , E2 != 0, then E1 != E2 which would violate conservation of energy. Is this line of reasoning correct? if not, why?
Why do you think it's obvious? It is not.
There is a possibility that E2=0. See Lawrence Krauss' book "A Universe from nothing", for example.

How do we know that the big bang is the origin of time and not just an event that happened in time? Is there a mathematical/scientific reason or is it an axiom we have adopted?

If total universal energy is not conserved in GR , is it still conserved in isolated systems? Is it also true that universal E conservation does not apply to SR?

As for the current total E being 0... How is this possible? Wouldn't that mean nothing can happen?

phinds
Gold Member
2021 Award
How do we know that the big bang is the origin of time and not just an event that happened in time? Is there a mathematical/scientific reason or is it an axiom we have adopted?
We don't know, we just have a model that represents reality incredibly well and as has already been stated, it is unable to handle what happened at or before the big bang singularity (aka t=0) or if there even IS a "before".

If total universal energy is not conserved in GR , is it still conserved in isolated systems? Is it also true that universal E conservation does not apply to SR?
Just today I made a post claiming that energy is conserved in closed systems and was told that that is wrong. See here: