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

Expanding in what?

  1. Nov 7, 2011 #1
    It may be a silly question , but sometimes I ask it to myself :

    If the universe is expanding , throw what is it expanding ? There is no "place" because the place itself is expanding , and there is nothing at all , so how can galaxies become far and far from each other ?

    If the place is the gravitational field which spread in the speed of light , so what is the "nothing" or "no field" or "no place" which place is expanding in?
     
  2. jcsd
  3. Nov 7, 2011 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    It is not expanding into anything (nor is it expanding into "nothing"). According to currently understood cosmology, it's all there is.

    As for how can it be getting bigger, that's no problem at all. Google Hilbert's hotel
     
  4. Nov 8, 2011 #3

    Drakkith

    User Avatar

    Staff: Mentor

    According to accepted models "The Universe" is not a physical object outside of which there are other physical objects (universes). Instead it is literally EVERYTHING there is. There is no outside, no boundary, nothing. Instead of visualizing "The Universe" expanding, simply realize that what is meant is that the distance between all objects is increasing over time. That's all there is to it.

    You can find more in the FAQ section.
     
  5. Nov 8, 2011 #4
    This is the standard model which is based on observations. I agree that it is almost impossible to visualize and goes against everything we see in every day life. The infinite and the infinitesimal are both very baffling and impossible to observe. One thing that seems to be finite is the age of the universe from BB.
     
  6. Nov 9, 2011 #5
    Here's an oddball thought... What if the universe isn't expanding, but instead everything is contracting and being correspondingly scaled down. The space between objects in the universe would appear to be expanding while everything in the universe shrinks by the same amount. The speed of light would appear constant because as it slows down every method that we have of measuring it would also be scaled down.

    Is this a kind of hyperbolic thought-projection of the concept of expanding space? :confused:
     
  7. Nov 9, 2011 #6

    phinds

    User Avatar
    Gold Member
    2016 Award

    That particular piece of utter nonsense gets dubunked here fairly often. Do a forum search if you really want the details of why it doesn't work
     
  8. Nov 9, 2011 #7
    Hmmm... Well I wasn't serious about the concept, not least because of Occam's Razor, but I thought that with it being a "scale factor", it could perhaps be understood from the reverse perspective.

    Having given it more thought and a bit of reading I'm of the impression that everything including many of the constants of nature would need to be scaled down equally, including but not limited to the speed of light and it's wavelength as it travels. This "tired light" theory has been comprehensively ripped apart over many years in relation to the standard theory of cosmology. I guess it really would be a horrific task to scale all those parameters. I'm still wondering what the quivalent of dark energy, inflation and the singularity at t=0 would be in a shrinking universe though and whether it would be any less understandable than the standard concept.
     
  9. Nov 15, 2011 #8
    Thanks for reply, friends.

    I really enjoyed all of what was written here, and I admire your minds and way of thinking.


    I think the age of the universe is not actually finite, because we can't achieve the begining point of the big bang, because it is not definite !!

    If we were going back in time, we wouldn't get the singularity because the time would be slower as we become nearer to the singularity and we wouldn't get the first point in time even if we were going back forever, and the singularity would represent the "absolute past". That resembles what would happen if someone fell in a black hole, they wouldn't reach the center of it ( the singularity ) and it would then represent the "absolute future"

    mathematically the singularity is not defined , like the function : f (x)= 1/ x at x = zero or at y= zero. The curve will approach x-axis and y-axis and get nearer and nearer but it will not touch them.


    I think both absolute past and future are equal to the absolute zero in thermodynamics where the energy is zero.
     
  10. Nov 15, 2011 #9

    phinds

    User Avatar
    Gold Member
    2016 Award

    You are of course free to believe any nonsense that you care to believe but keep in mind that the universe does not care what you believe, it just does what it does. There is no evidence of time changing characteristics as we approach the singularity so this is pure speculation on your part. There is also no evidence that matter does not reach the singularity of a black hole. This also is just personal, unsupported, speculation on your part. It LOOKS like (to an outside observer) that matter slows down as it falls into a black hole, but that's just an artifact of a different frame of reference. The infalling matter doesn't care what the external observer sees, it just keeps on heading for the singularity and it does get there.
     
  11. Nov 15, 2011 #10

    Drakkith

    User Avatar

    Staff: Mentor

    What reasons do you have to believe this is true? On the contrary we have every reason to believe that there was a definite point in time when the big bang occured.

    Time never changes for an observer. If you were falling into a black hole your sense of time would remain unchanged. It is only when you compare different frames that time dilation occurs.

    I don't even know what absolute past and future are. Did you come up with these or are they actual concepts?
     
  12. Nov 15, 2011 #11
    I would think relative point in time instead of definite point, after all it is and we are still dilating one second per second.
     
  13. Nov 15, 2011 #12

    phinds

    User Avatar
    Gold Member
    2016 Award

    So do you or do you not believe that exactly 8am on Oct 2nd 5,000 BC (as counted backwards using our current calendar) was a definite point in time? I take it you believe that was a relative point in time. I believe it was a definite point in time.
     
  14. Nov 15, 2011 #13

    Drakkith

    User Avatar

    Staff: Mentor

    I'm unsure as to what you are saying.
     
  15. Nov 16, 2011 #14
    That is an interesting idea, the concept of absolute time as opposed to relative time. If we all (well Physcists at least!) changed our clocks to Big Bang time ie. t=0 which is an absolute point in time that everyone in the universe certainly must agree on, would this help at all in our understanding of the evolution of the Universe, and some of the current problems faced in Cosmology? I am guessing it is already being done this way.
     
  16. Nov 16, 2011 #15
    Ossama, I have wondered that also, that perhaps the passage of time slows down to zero as we approach the BB "singularity". If true would this mean that the age of the Universe from the time of the singularity is infinite? Where is Chalnoth when we need him?!
     
    Last edited: Nov 16, 2011
  17. Nov 17, 2011 #16
    Although this is an other point may seem metaphysical more than physical, but according to the philosophy of uncertainty principle we may say that the observer of the physical experiment is a part of it, because without the observer, the experiment has no meaning.

    The evidence is in general relativity. Time becomes slower in a proportional way to the intensity of the gravitational field, so the nearer we become to the singularity, the time is slower until it has no meaning and cannot reach the singularity, because JJ simply _ it is singularity !! It is not a definite point in the time/space.
    I know that may seem absurd, but these are my thoughts with which I understand our universe, and there are some contradictions __ I admit __ but for those contradictions I opened this topic.:smile:


    The singularity is same everywhere ! , because it is not related to the past history before it formed, so the singularity of the big bang is the singularity in a black hole, just an indefinite point in time/space, and we can't say that it contains matter, and all of this is related to the formation of zero-energy universe in which the total amount of positive energy and negative energy equals zero.


    These are my expressions ( I don't know anyone used them before ) , I used them in Arabic __ while I was speaking about singularities __ and I translated them into English, so I put them in parentheses ""

    I mean by absolute past and future that we cannot reach them even if we go forward or backward in time forever.
    I remember something like that which Hawking said. I will search for that.
     
    Last edited: Nov 17, 2011
  18. Nov 17, 2011 #17
    That I wanted to say dear Tanelorn, so I put the function f(x) = 1/x at points x = zero , and y = zero as a resembling case to the singularity under study !

    Notice that we can calculate the area under the curve from x=0 until x = a, but the curve cannot reach the y-axis even it is getting approach to it and to x=zero, because y would be then equal to infinity !

    Maybe singularities are mathematical expressions more than real physical things !
     
  19. Nov 17, 2011 #18

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I agree. This is true essentially by definition. Because a singularity is a failure in a manmade theory, not something that exists in nature.

    This is the conventional view. You will find this discussed in the essay "A Tale of Two Big Bangs" at the Einstein-Online link in my signature.

    ==quote E-O "A Tale of 2BB"==
    Most cosmologists would be very surprised if it turned out that our universe really did have an infinitely dense, infinitely hot, infinitely curved beginning. Commonly, the fact that a model predicts infinite values for some physical quantity indicates that the model is too simple and fails to include some crucial aspect of the real world. In fact, we already know what the usual cosmological models fail to include: At ultra-high densities, with the whole of the observable universe squeezed into a volume much smaller than that of an atom, we would expect quantum effects to become crucially important. But the cosmological standard models do not include full quantum versions of space, time and geometry - they are not based on a quantum theory of gravity.
    ==endquote==

    Also check the FAQ right here at cosmology forum.

    To repeat in more detail: singularity is not imagined to really exist in nature.
    A singularity is a breakdown in a manmade mathematical model. A point (or larger region) where the equations fail and stop computing meaningful numbers.

    Normally in physics when singularities appear in some theory they are treated as a symptom that the theory has reached its limits. It is a call to fix the theory or replace it by a better one that will not break down where the old theory did.
     
    Last edited: Nov 17, 2011
  20. Nov 17, 2011 #19
    With or without the singularity, is the passage of time affected when the universe is very young and therefore very dense? And could this therefore effect our estimates of the age of the Universe?
     
  21. Nov 17, 2011 #20
    @Tanelorn: I'm not certain if it would make any sense to consider the passage of time itself, as a whole, to change. It seems to me that the passage of time can only be measured against the passage of time somewhere else, eg. close to vs. further from a gravity source. For the passage of time of the whole universe to be "affected", aren't we lacking something against which to measure it?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Expanding in what?
Loading...