Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What causes space time to come into existence?

  1. Aug 10, 2008 #1
    Forgive me if this is a stupid question, I'll be trying to come up to speed over the next few weeks.. I am trying to recall a model of the universe that stuck in my head from a few years ago.

    -Does space-time's existence rely on the presence of mass?

    -When people say that space-time expanded at beyond the speed of light after the big bang, was space-time already there or did it come into existence as a result of the bang (assuming there was no matter present before the big bang)

    -If space-time is a consequence of the big-bang, does that mean that light can only travel so far from mass before any direction leads closer to the universe again (as a result of space warping)?
     
  2. jcsd
  3. Aug 10, 2008 #2
    This is a purely theoretical topic and any answer I give will be called into question by those who “know better” but I will answer anyway.


    Does space-time's existence rely on the presence of mass?
    If you examine the equality: e = m/c^2 and divide both sides by m, you get:
    E/m = c^2. c is velocity which is distance/time. Using the word “space” instead of distance you get:
    E/m = (space/time)^2
    so the existence of space-time is equivocal to (dependent upon) the existence of not just mass, but the existence of the energy/mass ratio.

    -When people say that space-time expanded at beyond the speed of light after the big bang, was space-time already there or did it come into existence as a result of the bang (assuming there was no matter present before the big bang)


    I have not heard people say that. As far as we know, the max velocity allowed in this Universe is the speed of light.
    If e/m existed prior to the BB, then space/time also existed. But the singularity is defined as infinite mass radiating no energy, which is an undefined condition which no one can understand. But if that is the case, then the other side of the equality would be an infinite time which has no spatial dimension, which is equally beyond our understanding. Our understanding of the Universe must begin after the BB in which we have energy and mass, space and time. Which condition gave birth to which other condition is dependent upon which way you want to traverse the equal sign and is probably beyond the scope of human understanding at present.

    -If space-time is a consequence of the big-bang, does that mean that light can only travel so far from mass before any direction leads closer to the universe again (as a result of space warping)?

    I think mass and energy are “entangled” in much the same way that we now view quantum entanglement. No matter how far light may travel from the mass from which it originated, it remains always tied back to that mass in some manner. In other words, energy is never completely free of mass; energy and mass always exist as a ratio. That is what Einstein was trying to tell us. No matter how far light travels, it cannot ever escape from that ratio if it did the velocity of light would be infinite. If you want to consider that as space warping, that is as good as any other explanation.
     
  4. Aug 10, 2008 #3
    Questions one and two
    Think about what space-time actually is. It is usually considered as everything within the "boundaries" of the universe. Spacetime is space and time as we know it. Before the big-bang, we assume there was nothing. No universe, nothing. Of course, you could argue that there was a heck of a lot of emptiness around, and who knows, there probably was. But there was nothing else.

    Then the Big-Bang happened, and suddenly there was something in all the emptiness, and this is what we call spacetime. From the point we could measure time and space, (not as in when man invented the ruler and the clock, but when there actually was something to measure), spacetime came into existence.

    So in conclusion of your first question, spacetime relies on the presence of "something". If there is "something" in a spot, then space-time exists. If you can visualize a 3D-grid on a computer, that is spacetime. Spacetime is just a term for the "volume" (Space) around us, and the changes happening therein.

    Question three

    This is pretty hard to answer, but mine would be "not really". I'm not telling you that light wouldn't perhaps come back to the universe at some time, but I don't think you can say that spacetime has something to do with it. Light might bend back because of the massiveness of the universe, but strictly speaking, light moving at the "edge" of the universe, away from everything else, is actually expanding spacetime (the volume) of the universe.

    Hope things made slight sense. This gave me a pretty good think-through of what spacetime is, too. Thanks ;)
     
    Last edited: Aug 10, 2008
  5. Aug 10, 2008 #4

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    No. There exist models in general relativity which are "empty," i.e. there is no matter in them.

    Contrary to popular belief, the big bang theory does not state what happens at the actual "time of the big bang" but rather states that the universe was once in a much more dense and smaller state than it is today, and has expanded from that state. There are models which are trying to answer the question of what happened in the beginning (see some of marcus' posts in other threads, for example), i.e. they are trying to break through the singularity, but there's nothing to say that these are correct.
    I'm not sure I understand this question.
     
  6. Aug 10, 2008 #5
    Be careful there. The speed of light barrier apply to motion of objects in space but doesn't apply to expansion of space itself.
     
  7. Aug 10, 2008 #6
    Yenchin: Tell me, what is space? If space is to expand, my idea is that there has to be something in it, be it photons, a cloud, or a shoe, pushing the edge of space along. If space is a lot of nothingness, then, in my opinion, it is already there, and not expanding.
     
  8. Aug 10, 2008 #7
    Of course, you are right! I was speaking of linear velocity. If space is contained within a spherical volume, and R (Radius) is increasing at the speed of light, then the Volume of space is increasing according to:
    V = 4/3 pi R^3. Obviously this is more than c, but only because it is a cubic measure instead of a linear measure.
     
  9. Aug 10, 2008 #8
    This is the whole thing, that I think is frequently misunderstood. I understand space-time to be the very matrix of dimensional space. take that away and you don't have an empty space, you simply have nothing.

    And as space-time is known to warp around mass, it cannot fit the definition of empty nothingness, it is the matrix of the emptiness itself. So as it expanded so rapidly after the big bang, the boundary of space-time must have spread then slowed somewhat. My question mostly pertains to this 'boundary' of space time that is spreading outwards; can light over-take it, or would it follow the warp and double back..

    Does anybody understand that?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: What causes space time to come into existence?
  1. What causes orbit speed (Replies: 18)

Loading...