Physicists simulate critical 'reheating' period that kickstarted the Big Bang
phys.org
phys.org
Just before the Big Bang launched the universe onto its ever-expanding course, physicists believe, there was another, more explosive phase of the early universe at play: cosmic inflation, which lasted less than a trillionth of a second.
But cosmic inflation was part of the Big Bang, not something that happened “before” it. According to the current understanding, the Big Bang included the beginning of time itself—in more technical terms, the Universe has no boundary in time (or space)—so asking what happened “before” the Big Bang is akin to asking what’s north of the North Pole.
The universe may or may not have a boundary at the big bang. Most straightforward theories seem to suggest it does have one. I believe Hawking has a rather complicated theory where it may not have one, but that involves adding an extra time dimension, which is a bit iffy.
Regardless, even if an infinite (in space) universe simply sprang into existence at a certain moment, that still doesn't mean it makes sense to ask what happened before. It makes sense to ask what happens at the boundary, but there is not necessarily a before to ask about.
A ball is like a 3D manifold for the same reason, but it also has some points where you don't have a neighbourhood that looks like 3D space but rather one that looks like half of 3D space. That region is the boundary, so to be exact a ball isn't a 3D manifold but a 3D manifold with boundary.
The surface of a ball, i.e. a sphere, doesn't have boundary for the same reason that the surface of the Earth doesn't. You can't travel along it and eventually reach some kind of edge. That is, no matter where you are on the Earth, you can in principle, move freely along any coordinate direction and still stay on the surface of the Earth.
Thinking of the entire volume of the Earth, however, is akin to considering a 3D ball. Inside the earth, magma/rocks/etc can, in principle, move freely along all 3 axes. However, once we're at the surface, one of our axes of movement is restricted. We can't go further "out" and still stay within the ball (of the Earth).
As @contravariant hints at, the above can be made precise by using the mechanics of topology to get something called a (topological) manifold. If you're at all inclined, I highly recommend taking some time to get familiar with topology. It's an amazingly deep field with applications in almost any field you can think of!
Not precisely correct, no; there certainly was time before inflation ended, and there may even have been something equivalent to a traditional big bang, but our bubble universe started right then.
The travel time for light from that event doesn't seem to tell us very much about how old the Universe is as an n-dimensional space. It only tells us how far back we can observe. We can choose t_0 to be the point in time at which that farthest emitted light was emitted. That doesn't mean there isn't a t_-1, it only means that our axis of positive time starts there because that's all we can observe right now. We know some event happened and before that event we can make no observations, while after that event we can make observations. So everything observable follows from that event. But absence of observations is not evidence of absence.
It's actually sensible to ask what's north of the North Pole because it reveals something about the geometry of the coordinate space. You're considering the North Pole as a fixed boundary where all lines end, whereas the asker considers it as a point that all lines pass through(this is a more correct interpretation). In our polar coordinate system going to that point would result in being somewhere south of north but on the other half of the semicircle. Whether it's sensible to ask that about the universe seems like an open question to me.
The sensible thing to me is to wonder at the question while recognizing that we aren't currently able to answer it sensibly. Maybe we never do.
Cosmological models of the early universe tend to naturally break up into several phases, e.g. the inflation period, baryogenesis, and (much later) nucleosynthesis.
Given how sketchy our data gets the further back we try to probe, it's certainly not unreasonable to say that "Big Bang" refers to the point at which inflation ended.
Heck, even inflation itself is something that's hotly debated, and the search for evidence of an iflation field is an extremely active area of reseach.
> According to the current understanding...
Feel like you've been misled. What you describe there is a summary of an idea for a model that is particularly beautiful mathematically.
Once we have a solid, evidence-backed model going back so far, I suspect the Quantum Gravity nut will have already been cracked for some time.
https://www.youtube.com/watch?v=chsLw2siRW0
> all with known physics
Um... I'd like to see their "known" theory of quantum-modified general relativity...
None of this really matters because only depressed people worry about the "meaning" of life, primarily because they have been denied all other sources of "meaning" and therefore cling to the one thing everyone (including themselves) has: a life. It's only human to grow attached to things and our lives are our most priced possessions after all.
Can you expand on the only selects one philosophical zombie? I don't really understand what you're attempting to express.
I think all people "think" about existence at some point. Maybe sad people think about it more than others.
I'm an exmormon/agnostic that believes in afterlife just not deity. I don't believe 100% just that it's possible, but that there's no pre-requisites to get there and no conditions. Mainly energy that is our 'soul' lives on in some form, or maybe there is quantum imortality where you keep being reborn in 'yourself' in another parallel universe and you retain some memories/essence of your former self, but are always trying to become better.
You or someone else could have a child in one universe, not the next. So in some universes you're never even born, some you are, and some people may be born for the first time ever, thus the whole old-soul/new-soul thing. Who's to say though it's not the same universe just it swings back and forth like a pendulum and when it's in the low arc it's our small time here, when it's at the high mark it's sucked back into a dense ball, then it explodes again on the downward arc...
I just can't buy that an all-knowing all-powerful being created everything (if anything it was an idiot who blew up all space/time toying with technology they didn't fully understand). This same being is petty, manipulative, and narcissistic and demands our fealty, our faith, our worship else we be cast into a pit of fire. Sounds like something Donald Trump would say to pretty much any Democrat or anyone who doesn't think his shit is made of gold.
Though the entire universe could just be like a wave that spreads out, and then back in and back out and back in eternally. Whether each iteration is a mirror of itself or 100% different nobody will probably ever know.
I don't think we'll ever have answers even if we colonize the entire universe. There's a good Asimov short story on entropy where they keep asking a super computer if they can stop entropy and for eons it keeps saying unable to compute and just before entropy runs out it came up w/ a solution.
Mankind became immortal (or long-lived at least) and had populated the entire known universe. Damn, I'd love to live to see that.
If universes get reborn ad infinitum, nothing is that final.
https://science.howstuffworks.com/dictionary/famous-scientis...
It hasn't ended yet so it makes sense that either space time is static or that there is an infinite chain of big bang like events.
"we not only don’t know whether there was a singularity at some point in the very distant, pre-inflation past, or whether inflation was truly eternal, we don’t even know whether inflation occurred for less than a yoctosecond or more than the present age of the (post-Big Bang) Universe!
Our prospects for finding out, furthermore, are quite dim, as — by its very nature — practically every model of cosmic inflation wipes out any information about the Universe that existed prior to the last billionth-of-a-yoctosecond before inflation ended, and our Universe began."
"It may have been eternal to the past, there may have been a true singularity before it, or there may have been something else; as far as our current observations go, we haven’t even conceived of a way we could possibly know."