I often hear it said that time and space did not exist before the Big Bang. What does that mean exactly? I understand that anything that happened “before” the Big Bang would have no effect on the present universe, so in that sense, time before the Big Bang is meaningless. However, we can talk about height in Flatlandia even though no inhabitant has an height. When one says that time and space were created by the Big Bang, does this just mean the time and space that contain anything created by the big bang, or does it mean that space is a thing rather than a lack of things (if that makes any sense)?
Yes, it does mean that space is a thing. That’s the whole notion behind Einsteinian four-dimensional space-time. Space is a thing, mass warps space creating gravity, etc. And the equations of relativity cannot be applied to anything previous to the creation of our universe, which is why it is said that space and time started with it.
We can talk about height in Flatlandia, because we are three-dimensional creatures. They cannot talk about height, except as a mathematical, but not physical, notion. In the same way we can talk about 11-dimensional M theory but cannot understand physically what those extra spatial dimensions are.
Science currently can’t say anything meaningful about the Universe “before” the Big Bang. Even “the Big Bang created the Universe” isn’t really correct. Instead “the earliest state of the Universe (including its constituent matter, energy, space, and time) which science can describe is the Big Bang” is better.
Given that time is a part of the Universe, there is no “before the Big Bang”. An analogy: there is no north of the North Pole.
So we can talk about spacetime existing outside the confines of the Universe in the mathematical sense, but they aren’t real. Is that what you mean? When we speak of warped spacetime, is this just conceptual, in that bodies follow these curved paths as if they were traveling on a warped sheet, or is it deeper than that?
Also, unlike the Flatlandians, we exist in 11 dimensions if M theory is correct.
Here picture of the universe, in which time is the horizontal axis and at each time our 3 spatial dimensions are represented by a flat 2-D disc. If the universe is spacetime (per Einstein’s Relativity), then it makes no sense to talk about “outside” this shape. That shape is all there is.
Now, indeed, M theory or the like might say that this shape is atached to other shapes, perhaps of different dimensionality again, or even that the North Pole of the universe (or “Big Bang”, although I’d like to see it renamed the Big Bell End :)) is actually the point of collision of two other shapes (the Big Splat - this is all getting too Viz for me).
But, whatever, the point is that there is no time at which there was no universe. One could say that the universe has always existed, even if “always” isn’t an infinite amount of time.
But isn’t that the same thing as saying that there is space and time outside of the expanding universe, but anything that happened then or there has no effect on our universe? Why is it not correct to think of the universe as an expanding sphere in 3-space? Why does the universe have no center?
Positing other “attached” shapes is, I suppose, positing spacetimes other than “our own”. We’re still not sure whether they are wholly inconsequential to “ours” - even thought that may well be true, I rather think that’s jumping the gun.
That’s the only feasible explanation for the galactic redshift and Cosmic Microwave Background, rather like evolution is the only feasible explanation for the fossil record.
Because it’s everything. The surface of a spherical balloon has no centre either - any point on it is as arbitrary a choice as any other. When you inflate the balloon, the points on it get further from each other without moving - it is the space between them which expands. The Big Bang is the universe - our entire spacetime expanded and continues to expand such that all galaxies move away from all others (OK OK, except locally gravitationally bound ones). The universe is not expanding into something else.
Oh, sorry, I misread the question. An expanding sphere in 3 space would be expanding into extra space, and we’d be right back where we started trying to understand that space (to say nothing of the effect on gravity). Expansion in 4 space yields the gravity strength we do indeed observe, and avoids those problems of circularity.
According to Einstein space is curved in the same sense as the surface of a sphere is curved. (Whether we live on a 3-sphere or a different type of curvature is a different issue.) It’s real and it’s the fundamental property of space.
Talking about spacetime without space makes no sense using relativity, not even mathematical sense. Quantum mechanics does provide some way to look at the situation, mostly by showing that a minimal amount of energy must exist in any potential space, but until we can combine relativity and quantum mechanics into a so-called Theory of Everything - of which M theory is a possibility, not yet proven and certainly not entirely understood - we have no language for a full description of what happened before the Big Bang.
A philosophical retort to the OP, rather than scientific: it’s because time is a function* of motion, and space is a function* of distance. Before the big bang (I guess is the theory) there was neither motion nor distance between things. So you would not have time and you would not have space.
This is key to the critical difference between the concepts of Something and Nothing.
*“Function” isn’t really the word I want, but I can’t think of a better one right now.
I am sorry, but I still don’t get it. Why isn’t the Big Bang like an explosion in that we are bomb fragments moving from the initial position of the explosive? Why aren’t we expanding into empty space? How is space different from nothing? This concept completely eludes me.
I would understand it if you say that time and space have no meaning outside of the confines of the universe or before the Big Bang, in the same way that if nothing ever moved, time would have no meaning, but apparently, that is not the case.
An earlier poster seemed to state that once a ToE is worked out, we can talk about time before the Big Bang and about space outside the universe.
I must also confess that I don’t understand how physicists can declare this to be so. What about our sense that time exists? Does that come from this intrinsic property? Is it unrelated? Are we not relevant to the matter at all?
It’s completely unintuitive, I know. However, all current understanding points to the fact that space is created by the Big Bang.* Space could not have been there before the universe. That’s part of the definition of universe. The universe is all of space. There is nothing in our universe that is outside our universe.
You just have to wrap your head around this to get any farther, I’m afraid.
That was me, oddly enough. But I carefully didn’t say that we could talk about time before the Big Bang. I said we could give a mathematical depiction of where our universe came from and why it has the properties it has. That’s very different.
What time is and why we perceive time is a matter of furious debate among physicists, not to mention philosophers who understand nothing of science even though they write about it. But of course we’re not relevant to the matter at all. How could we have such hubris as to think otherwise?
*For the nitpickers: I know that Big Bang is a totally inaccurate term to use for the creation of the universe or even for the inflation that made it our size. But it’s a good general shorthand for the topic and I really don’t want to get into the ways it’s wrong, because that would totally confuse an already confusing subject. If you want to make something of this, start another thread.
I don’t think it’s hubris to ask that question. If we’re not here, the questions don’t exist. The furious debate among physists about the perception of time is exactly what my question is about. That we all perceive time in some fashion should tell us something beyond, or aside from, mathematics. Something intrinsic, indeed, but something, perhaps, unrelated to quantum mechanics. Maybe time is more than one thing. Maybe there are different types of time. But our relationship with time is not unreal any more than our lives are. If consideration of that is hubris, so be it.
To the contrary: it’s completely intuitive if you’re not allergic to a little math. The problem with all these threads is the questioners wanting us to explain everything to them in these vague, hand-wavy terms and then complaining when they misinterpret us.
The Big Bang was not an explosion of something into nothing. The Big Bang was an expansion of the entire universe (all matter, energy, space and time: everything). As ExMap says, this is the essential point that you must somehow understand.
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In my understanding, the basic mechanism of time is well understood by physicists. It’s just another coordinate in space-time. As for human perception of time, that is a neurological/psychological question.
Physics tells us what time is and how it works. Neurology et al. tells us how we perceive it. Similarly to color and sound: physics describes the phenomena, psychology describes the perception.
Jeez, I don’t know how you got there from my post. That’s a hell of a leap and an unwarrented assertion. Are you suggesting that there are scientists who can examine the universe from any other perspective than their own?
Let me just say up front that I respect you and the insight you offer to the SDMB on a very regular basis. I’m always blown away by those that have not only the raw intellect required to obtain the mathematical skills that you and others do, but the investment in time and learning. I’ve seen your responses in this forum over the years to only really gleam your level of skill in these matters and not much else. Now take a guy like me, who has a deep and profound love for these topics and the hard sciences in general. While I wouldn’t consider myself unintelligent, my math skills are somewhat lacking, but I’d like to think I make up for this deficit in other ways. I can only assume that the math required to fully understand these concepts are esoteric at the least, and would require years of training and diligence. I can only speak for myself, but I’d like to think that there are others who share a similar interest in these matters but don’t have the required training to grasp them “intuitively”. That is, it is not apparent to us from our humble experiences how these things work or came about. We require analogy or visualization. So far, the scientific world has been generous to us, and has allowed us to peek into some of the deeper truths to the universe without having to understand the “language” used to derive it. My only wish is that this generosity continues to be spread by those that truly grasp it and understand the language. Help us to understand.
