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

The universe may not be expanding!

  1. Feb 18, 2007 #1
    Greetings all! This is my first time at this forum. Any old pals here from our ruined playpen, pmb, kieth, bruce, sam, hector, nudnik, etc.????

    It has occured to me that the universe may not be expanding! Perhaps the "clock" for the universe speeds up as time moves forward. This may be why we observe a red shift if old light from distant realms which was emitted earlier in the history of the universe when the clock ran slower? You understand what I mean by the "clock" running faster as the universe ages, right? If not, say so and I'll try to explain better what I mean.

    The reasons for the clock of the universe speeding up would be open to speculation. At first glance this seems incredulous, bizarre and mysterious, but, no more so than an expanding universe.

    According to the principles of relativity from observations or experiments involving light we wouldn't be able to distinguish between an expanding universe and an universe that was running ever faster. Electromagnetic astronomy could not contain the information to tell the difference.

    It could also be that only our local "clock", either the clock for the Milky Way Galaxy or just the clock for our region of the Mikly Way. It could be that the central blackhole of the Milky Way is changing and thereby affecting the rate at which time progresses locally. This may have some connection to the observations leading to the postulate of "dark matter". A changing clock for the galaxy may produce the non-newtonian orbital velocities observed in a rotating galaxy.

    There may be a way to disprove the changing local clock idea from observing the red shifts of distant galaxies (i.e, time dilation of supernovae events), however, we still could not tell if the clock for the entire universe runs faster as the universe evolves.

    I just had an interesting notion writing this. The time field and the speed of time. At what rate would changes in clock rate produced by a time rate altering phenomae propagate through space?
  2. jcsd
  3. Feb 18, 2007 #2
    Isn't the "speed" of time relative?
  4. Feb 18, 2007 #3


    User Avatar
    Science Advisor
    Gold Member

    Hi chalieb and welcome to these Forums!
    You may be interested to check out Self Creation Cosmology - An Alternative Gravitational Theory.
    Hi Peter (IMC) and also welcome to these Forums!
    Yes, you need to compare two clocks to notice that one is running faster/slower than the other.

    Last edited: Feb 18, 2007
  5. Feb 18, 2007 #4
    Thanks Garth, It´s a pleasure to be here.

    I remarked that the "speed" of time is relative to point at the idea that it is not possible that the "clock" of the universe is speeding up.

    However, I thought about this idea as well, and as far as I understand it, the "speed" of time in fact depends on our speed compared to the speed(s) of what we´re observing.

    Makes me end up on another question I have been thinking about a lot. I read somewhere that the speed of light is in fact limited because it is the highest speed a foton can move through space. Which gives me the impression that space somehow gives some kind of resistance to a foton. If that is true, can we not measure how fast something goes through space it self?

    If speed is limited at the speed of light, isn't there a speed of absolute 0 as well? Wouldn't all time pass by in "no time" at 0 speed? (as the other extreme of time standing still at the speed of light.)

    I feel like I can finally talk about these things with people that "know" (at least know a lot more than I do :) ). I´m really happy I found this forum. Looking forward to some replies.
    Last edited: Feb 18, 2007
  6. Feb 18, 2007 #5


    User Avatar
    Science Advisor
    Gold Member

    Likewise. :smile:
    First let us clear up our terminology to save confusion. I would restrict the term "speed" to refer to the rate of movement through space. You might want to ask about the "rate of passage of time", however that is a tautology, time can only pass at the rate of one second per second.

    What you can observe is time dilation, most familiarly caused in SR by relative velocity - a clock moving relative to yourself is observed to run more slowly than the one on your wrist, and a clock sent on a long journey and back will be found to be 'slow' compared to a stay at home identical twin.

    In GR we also observe gravitational time dilation, a clock at the bottom of a gravitational well is observed to run slowly compared to an identical twin at the top. A clock lowered slowly into a gravitational well and returned will be found to be 'slow' compared to one that stayed at the top.

    However there are many types of clock the main ones being, atomic clocks (atomic frequencies) and gravitational or ephemeris clocks (orbital periods). In the standard GR theory these do keep the same time, however they might not, instead they might exhibit a 'clock drift'. For example, the Pioneer Anomaly could be explained by such a clock drift, see Relativity Theory and a Real Pioneer Effect

    In standard GR cosmology the cosmological clock is indeed assumed and defined by the Robertson-Walker metric coordinate system to be constant. Observed cosmological red shifts are interpreted as Doppler shift and the universe is therefore seen to be expanding.
    You need to read up on basic relativity theory such as the on line series Lecture Notes on General Relativity by Sean Carroll
    You're welcome.

    Last edited: Feb 18, 2007
  7. Feb 18, 2007 #6
    Clock rates

    Hi Garth. Hi Peter.

    Good point on compraring clocks Garth. When we look back into the past by oberving distant galaxies, could this not be interpreted as comparing the modern clock with the one in the past? We observe a red shift and could conclude the clock ran slower in the past. I don't see how this is could be distinguished from an expanding universe. Relativity indicates we could not tell the difference between the two states.

    I'll try to clarify the speed of time idea. Suppose we are observing a galaxy from outside along its axis of rotation. Some event or process causes a change in the clock rate starting at the center of the galaxy, at what rate would the change in clock rate propagate to the outer edges of the galaxy? Hmm... now that I say it words I may have answered the question for myself. I was sort of thinking clock rate would be influenced by the gravity field of the central black hole. If changes in the gravity are causing changes in clock rate they would propagate outward at the speed of gravity. Or would they????

    What would cause changes in the g-field of the central black hole? The accepted notion is that the black hole at the center of a galaxy grows more massive as it consumes ever more of the galaxy's mass. Using Planck's Law we can infer the black hole and its g-field while growing every more massive and intense would also become more localized. The gravity field would shrink. Gravity from the center of the galaxy would grow weaker in the outer halo of the galaxy. The weakening gravity would produce an ever faster clock. This collapse of the central g-field and/or its accompanying effect on clock rates might offer a mechanism for the non=newtonian orbital velocities responsible for the postulate of dark matter.

    Another related question I have for some time comes to mind. Can gravity bend gravity? We know the large gravity field of galaxies can bend light passing near it similiar to the way a lens bends or concentrates light. Could a g-field also lens or cocentrate another g-field in its region? This would also offer a mechanism for non-newtonian orbital velocities in galaxies. The halo's g-field is bending and concentrating the central mass's gravity into the disk or halo of the galaxy raising the strength beyond what would be expected from uniform Newtonian gravity. This might also explain the Pioneer Probe anomaly. The planet's are lensing the sun's g-field concentrating it into the plane of the solar system.
  8. Feb 19, 2007 #7


    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    The clock question is complicated, and has no easy answer since all clocks are local [at least according to GR]. I feel more confident on the gravity bending gravity question - can't happen. Any such effect would introduce a feedback loop into field theory. This is not observed and would require a destructive interference effect to preserve Lorentz invariance in the universe at large. That might be a mathematical possibility, but is not very realistic.
  9. Apr 1, 2007 #8
    Since space-time is invariant to scale and neither space nor time is absolute in general relativity, it follows that expansion of distance and contraction of time are fully equivalent.

    Think of a square sheet with an x and a y coordinate.
    If the sheet becomes more and more rectangularly shaped in the x direction could you say definitively that it is stretched in the x direction or that it is compressed in the y direction?

    But I could imagine that if certain constants were added to the theory to support some cosmological model that this symmetry might break. We would get some preferred orientation of space-time.

    Gravitational fields obviously interact with each other. In a two or more body situation you need to "add" all the gravitational fields to get the combined gravitational field. No one, so far, has found a simple gravity addition formula.

    For instance, take the simple case of a big mass and a small mass which is orbiting the big mass.

    We can calculate the gravitational field created by each individual mass. If we assume that the two objects are non-rotating point masses the solution for each of them is the so-called Schwarzschild solution. The Schwarzschild solution is very handable and even Wick rotatable.

    But the problem is how do we add these two solutions to get one solution that describes the combined gravitational field of the two masses. Usually when you "add" two or more Schwarzschild solutions you get approximate solutions that are non linear, non stationary, non Wick rotatable and that generate gravitational waves.
    Last edited: Apr 1, 2007
  10. Apr 2, 2007 #9


    User Avatar

    Staff: Mentor

    Good answer.

    charlieb, welcome to PF, but please be aware that idle speculation on personal theories is not allowed here. What you are speculating about contradicts what is known, so it is not a constructive line of discussion.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: The universe may not be expanding!
  1. Expanding universe (Replies: 8)

  2. The expanding universe (Replies: 43)