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Did the Big Bang happen?
#1
Did the Big Bang happen?
No, this is not a creationist or ID gotcha thread. Just gonna clear that part up straight from the get go.

My knowledge of physics is limited. I opted to take Ecology instead of Physics in high school, so, my knowledge is very limited. I’m not good at math. That’s what informed that decision. Still I find physical and cosmological topics to be super interesting and I was on a YouTube rabbit hole of videos discussing how the Big Bang theory might not be quite as set in stone as we think…

Now my first thought was, are they saying this because of religious apologetics? What’s their motivation here? Some commenters on said videos did have a clear religious bias. But others… were the opposite. I actually came across one commenter who accused the establishment of holding onto the Big Bang theory because “people are not ready to let go of the idea that the universe was ‘created’”. I thought that was very interesting, but I also doubt that commenter is a top physicist or cosmologist either. Of course neither are we (that I know of), but discussing is still fun.

So, what I’m wondering is… Is it possible that there was no Big Bang and that the universe simply always existed?

We seem to have a lot of evidence of the universe expanding. We also have evidence of cosmic background radiation from when the universe was hot. But do we have evidence that these things started from a singularity? Is that part of all of it truly known fact? How can this even happen since in order for such an event to happen it would have to be “outside” time, because it would be before the expansion of the space time fabric?
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#2
RE: Did the Big Bang happen?
(April 27, 2022 at 3:55 pm)JairCrawford Wrote: So, what I’m wondering is… Is it possible that there was no Big Bang and that the universe simply always existed?
Then you would need a real good argument as of why the cosmic background is so incredibly uniform. Places, in all directions, currently so far away that they can not possibly have interacted with each other if they were always so far apart, and yet....the temperature is the same down to a few micro-degrees.
Cetero censeo religionem delendam esse
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#3
RE: Did the Big Bang happen?
(April 27, 2022 at 4:00 pm)Deesse23 Wrote:
(April 27, 2022 at 3:55 pm)JairCrawford Wrote: So, what I’m wondering is… Is it possible that there was no Big Bang and that the universe simply always existed?
Then you would need a real good argument as of why the cosmic background is so incredibly uniform. Places, in all directions, currently so far away that they can not possibly have interacted with each other if they were always so far apart, and yet....the temperature is the same down to a few micro-degrees.

Right so my non-science savvy brain would conclude that we have good evidence that the universe was at one point smaller and a lot hotter than it is now. But like I said, do we know with absolute certainty that this was a result of blowing up from a singularity?
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#4
RE: Did the Big Bang happen?
I hope Poly drops in to explain more of the evidence.

As I understand it, Fred Hoyle came up with a steady state model that could explain Hubble's observations... like some kind of "gyrating universe." But the CMB and discovery of dark energy kind of blow all that out of the water.

Another thing to note about it "all starting from a singularity." Science isn't 100% on that. All it can tell is that the universe was very hot and dense at one point.

The big bang theory is a "history of the early universe" and not "an explanation of how the universe got here." But you seem to get a lot of this... hopefully others can shed some more light.
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#5
RE: Did the Big Bang happen?
(April 27, 2022 at 3:55 pm)JairCrawford Wrote: So, what I’m wondering is… Is it possible that there was no Big Bang and that the universe simply always existed?

We seem to have a lot of evidence of the universe expanding. We also have evidence of cosmic background radiation from when the universe was hot. But do we have evidence that these things started from a singularity? Is that part of all of it truly known fact? How can this even happen since in order for such an event to happen it would have to be “outside” time, because it would be before the expansion of the space time fabric?

We don't know how to model a singularity - it is by definition a breakdown of space and time.  Whether there was one or not is an open question.  However, it is clear that the universe was at one point very tiny (as you have said, expansion, background radiation, smoothness of spacetime, galactic evolution as we look back in time).

There are a number of proposals as to how the universe started.  One is the Hartle-Hawking no-boundary proposal, that says that the beginning of the universe involved space without time.  Only when space expanded did time start to form.

Another is that there was a quantum tunneling event that started the universe, followed by a rapid inflationary stage.

Both these are compatible with the idea that the total energy of the universe is zero.  That is, you can get something from nothing, because the universe is nothing.
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#6
RE: Did the Big Bang happen?
(April 27, 2022 at 4:08 pm)JairCrawford Wrote:
(April 27, 2022 at 4:00 pm)Deesse23 Wrote: Then you would need a real good argument as of why the cosmic background is so incredibly uniform. Places, in all directions, currently so far away that they can not possibly have interacted with each other if they were always so far apart, and yet....the temperature is the same down to a few micro-degrees.

Right so my non-science savvy brain would conclude that we have good evidence that the universe was at one point smaller and a lot hotter than it is now. But like I said, do we know with absolute certainty that this was a result of blowing up from a singularity?
Nope
Cetero censeo religionem delendam esse
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#7
RE: Did the Big Bang happen?
(April 27, 2022 at 4:08 pm)JairCrawford Wrote: Right so my non-science savvy brain would conclude that we have good evidence that the universe was at one point smaller and a lot hotter than it is now. But like I said, do we know with absolute certainty that this was a result of blowing up from a singularity?

No we don't, but how small do you think it was, as it was just "sitting around"?  You can run physics back in time accurately (until you hit new physics).  You can't have a static hot small universe just sitting there.  It doesn't work.  Such a thing either has to be rapidly expanding, or else it will collapse upon itself.

Also, the current state of the universe imposes conditions on the universe at earlier times.

The universe had to be very tiny - so small that we run into new physics.  It either needed to start via a sudden event, or through evolution of some primordial quantum state.  Then, it had to expand rapidly in order to give the level of uniformity (low entropy) we measure in the early universe.
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#8
RE: Did the Big Bang happen?
(April 27, 2022 at 4:17 pm)HappySkeptic Wrote:
(April 27, 2022 at 3:55 pm)JairCrawford Wrote: So, what I’m wondering is… Is it possible that there was no Big Bang and that the universe simply always existed?

We seem to have a lot of evidence of the universe expanding. We also have evidence of cosmic background radiation from when the universe was hot. But do we have evidence that these things started from a singularity? Is that part of all of it truly known fact? How can this even happen since in order for such an event to happen it would have to be “outside” time, because it would be before the expansion of the space time fabric?

We don't know how to model a singularity - it is by definition a breakdown of space and time.  Whether there was one or not is an open question.  However, it is clear that the universe was at one point very tiny (as you have said, expansion, background radiation, smoothness of spacetime, galactic evolution as we look back in time).

There are a number of proposals as to how the universe started.  One is the Hartle-Hawking no-boundary proposal, that says that the beginning of the universe involved space without time.  Only when space expanded did time start to form.

Another is that there was a quantum tunneling event that started the universe, followed by a rapid inflationary stage.

Both these are compatible with the idea that the total energy of the universe is zero.  That is, you can get something from nothing, because the universe is nothing.


Isn't there a limit to how far back the observations can go? And we can (apparently) know some things about what happened in the first few seconds of the expansion. But that is through sheer extrapolation, right? How much certitude is involved in these extrapolations? I assume a high degree, but I've never heard one way or the other.
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#9
RE: Did the Big Bang happen?
Doesn’t getting something from nothing go against the whole “matter cannot be created or destroyed; only changed from one form or the other” though?

And how can anything even “happen” “before time”?

Those concepts are tripping me up.
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#10
RE: Did the Big Bang happen?
(April 27, 2022 at 4:38 pm)JairCrawford Wrote: Doesn’t getting something from nothing go against the whole “matter cannot be created or destroyed; only changed from one form or the other” though?

And how can anything even “happen” “before time”?

Those concepts are tripping me up.

It is likely that the amount of matter and kinetic energy is exactly balanced by the amount of negative gravitational potential energy.  That is, they add to zero. This isn't proven, but it is plausible based on current data (and is required by some theories).

As for "nothing happening before time" - we don't have a good definition of quantum time. Our current concept of time likely emerged with the universe. The arrow of time is tied to causality and increasing entropy. What if the early universe didn't have causality or a direction of time (the primordial quantum state fluctuated backward and forward in time).

The idea behind the Wheeler-DeWitt equation is that the wavefunction of the universe does not include time. It simply exists. It is literally timeless. It cannot gain energy - it can only show various forms (and an expression of time is one of those forms, though we really don't understand time).
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