# Did the Big Bang separate space and time

Hello everyone,

I've come across a problem that i can't solve but which i find really interesting. I'm not here to ask where the big bang was because i've already read enough about that is was a singularity, so you could say that is was everywhere. But here my problem comes in, if the big bang was everywhere why wasn't it always. Relativity predicts that space and time are from the same type. So is the difference between space and time only created by the big bang, did it just choose to not affect time the same way it affects space. I really want to find out what is the main difference between time and space because there is another issue i'm struggling with. First of all I want to know wether a mass also bends space-time in the dimension of time. I do know that when a big mass is somewhere it bends the space and time with a factor depending on the distance to that mass but does it also bends the space and time when the "radius" isn't a distance but a time. To illustrate it we will say that if there was a black hole besides you now and it just disappears right now. Would the time still go slower for you now although the black hole isn't there anymore. I need the answers on those two question because if it is true that the big bang didn't affect time the same ass space and if time is still bended after a while it would mean that our time is still going faster because the influence the big bang had on our time is still getting smaller due the fact that it is always getting older.

Nugatory
Mentor
I really want to find out what is the main difference between time and space because there is another issue i'm struggling with.
As you've posted this as an I-level thread, you can start with Taylor and Wheeler's "Spacetime Physics" or equivalent. Until you have solid grasp of the concepts there, you will not be able to make sense of either black holes or the big bang.

First of all I want to know wether a mass also bends space-time in the dimension of time. I do know that when a big mass is somewhere it bends the space and time with a factor depending on the distance to that mass but does it also bends the space and time when the "radius" isn't a distance but a time.
Both space and time.
To illustrate it we will say that if there was a black hole besides you now and it just disappears right now. Would the time still go slower for you now although the black hole isn't there anymore.
That question makes no sense, because gravitational time dilation (which does not mean that "time goes slower for you") is calculated from a solution to the Einstein Field Equations of General Relativity, and there is no solution in which mass just appears or disappears. However...
I need the answers on those two question because if it is true that the big bang didn't affect time the same as space and if time is still bended after a while it would mean that our time is still going faster because the influence the big bang had on our time is still getting smaller due the fact that it is always getting older.
None of that makes any sense, probably because gravitational time dilation doesn't work the way you think it does.

PeterDonis
Mentor
2020 Award
if the big bang was everywhere why wasn't it always

I want to know wether a mass also bends space-time in the dimension of time

First, you should understand that these are two different questions about two different models that physicists use. The first one is a question about a model that is used in cosmology to describe the universe as a whole; this model is called "Friedmann-Lemaitre-Robertson-Walker spacetime" (or sometimes "FLRW" or "FRW" spacetime for short). The second one, given your illustration using a black hole, is a question about a model that is used to describe isolated objects; this model is called "Schwarzschild spacetime".

The reason this is important is that the right answers to the questions you are asking are only going to apply to those specific models; they will not tell you general truths about gravity that work everywhere, in all situations. If you want to understand gravity in full generality, you need to understand the theory that underlies both of the above models (and all the other spacetime models that physicists use). This theory is General Relativity, and the general equation that underlies all of the models is the Einstein Field Equation. Both of the models I described above are particular solutions to this equation (and they are different solutions, so they have different properties).

With those cautions out of the way, here are quick answers to your two questions:

(1) The "Big Bang" is a term that describes the hot, dense, rapidly expanding state that the universe was in at the end of the inflationary epoch. The entire universe was in this state, which is why we say that the Big Bang happened everywhere. But this state did not stay the same; the universe rapidly expanded and cooled and got less dense, and has been doing so ever since. So the Big Bang is not "always" because it was not a static state; it rapidly changed into something else.

(Note that your underlying intuition here seems to be that "relativity says space and time are the same, so everything that applies to space should also apply to time". This intuition is wrong, and the answer I just gave illustrates that. But to really understand why it's wrong, you need to learn the general theory, not just particular solutions.)

(2) Nugatory's answer, "both", is correct, not only as a general statement about possible solutions to the Einstein Field Equation, but as a statement about the specific solution you asked about, the spacetime of a black hole (Schwarzschild spacetime).

The singularities of the big bang and those of a non-rotating black hole are of a completely different type.

haushofer
Hello everyone,

I've come across a problem that i can't solve but which i find really interesting. I'm not here to ask where the big bang was because i've already read enough about that is was a singularity, so you could say that is was everywhere. But here my problem comes in, if the big bang was everywhere why wasn't it always. Relativity predicts that space and time are from the same type. So is the difference between space and time only created by the big bang, did it just choose to not affect time the same way it affects space. I really want to find out what is the main difference between time and space because there is another issue i'm struggling with. First of all I want to know wether a mass also bends space-time in the dimension of time. I do know that when a big mass is somewhere it bends the space and time with a factor depending on the distance to that mass but does it also bends the space and time when the "radius" isn't a distance but a time. To illustrate it we will say that if there was a black hole besides you now and it just disappears right now. Would the time still go slower for you now although the black hole isn't there anymore. I need the answers on those two question because if it is true that the big bang didn't affect time the same ass space and if time is still bended after a while it would mean that our time is still going faster because the influence the big bang had on our time is still getting smaller due the fact that it is always getting older.
Hi Willem, welcome on PF! ( en als je Vlaams bent, veel plezier vanavond met de wedstrijd België-Wales ;) )

The Big Bang is not being considered as "an event which created space and time". It is considered to be a limiting point where our classical theory of gravity, GR, breaks down. We need a theory of quantum gravity to say something sensible about "what happened during the big bang". You can compare it with the usual thermodynamic description of water, which breaks down at phase transitions because of singularities.

It seems like you're also asking whether spacetime geometry can be time-dependent ( wether a mass also bends space-time in the dimension of time) . Yes, it can be; examples are the FRW-solution describing cosmology or the Kerr-solution, describing rotating black holes.

Hope this helps.

martinbn