Cosmology News

Arrow of time points to missing dark matter?

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Time doesn’t go backward, and that is a problem in current physics.

From Quanta:

Why should the fundamental laws have that bizarre and problem-posing property, T invariance?

The answer we can offer today is incomparably deeper and more sophisticated than that we could offer 50 years ago. Today’s understanding emerged from a brilliant interplay of experimental discovery and theoretical analysis, which yielded several Nobel prizes. Yet our answer still contains a serious loophole. As I’ll explain, closing that loophole may well lead us, as an unexpected bonus, to identify the cosmological “dark matter.”

We are told, there are “grounds for optimism.” A theortical paarticle called the “axion”:

The theory of axions predicts, in a general way, that axions should be very light, very long-lived particles whose interactions with ordinary matter are very feeble. But to compare theory and experiment we need to be quantitative. And here we meet ambiguity, because existing theory does not fix the value of the axion’s mass. If we know the axion’s mass we can predict all its other properties. But the mass itself can vary over a wide range. (The same basic problem arose for the charmed quark, the Higgs particle, the top quark and several other others. Before each of those particles was discovered, theory predicted all of its properties except for the value of its mass.) It turns out that the strength of the axion’s interactions is proportional to its mass. So as the assumed value for axion mass decreases, the axion becomes more elusive.

Do axions exist? We still don’t know for sure. Their existence would bring the story of time’s reversible arrow to a dramatic, satisfying conclusion, and very possibly solve the riddle of the dark matter, to boot. The game is afoot. More.

We expect it will be going on for a while.

See also: Cosmologist tells us how time got its arrow Something is wrong here. Just recording, just recording…

Studying time’s arrow with philosophers

Did time’s arrow originate in a quantum source?

and

The bill arrives for cosmology’s free lunch

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7 Replies to “Arrow of time points to missing dark matter?

  1. 1
    Mapou says:

    My comment at the end of Quanta’s crackpot article is still in moderation. I copied it below:

    Aw, come on, people. Time cannot change by definition. This is the reason that Karl Popper compared Einstein to Parmenides and called spacetime “Einstein’s block universe in which nothing happens.” Source: “Conjectures and Refutations”.

    Nothing moves in spacetime. Why? It’s because motion in time implies a velocity in time which would have to be given as v = dt/dt, which is nonsensical. That’s it. There is only the present. A time dimension is abstract.

    PS. The unchanging and abstract nature of time has been known for ages. Why does the physics community act as if has no clue?

    Here’s a link to Popper’s paper: Conjectures (PDF)

    [edit:] I suspect Quanta’s moderators will trash my comment. The physics community is gutless like that. LOL

  2. 2
    Aleta says:

    Crackpot comment? So the hare never catches the turtle, and the arrow never moves? I believe Zeno brought these problems up long ago.

  3. 3
    daveS says:

    Time cannot change by definition.

    I’m still trying to understand what this is supposed to mean. Have any reputable physicists or philosophers spelled it out in greater detail than “v = dt/dt is nonsensical”, or “time is abstract, bruh”?

  4. 4
    Mapou says:

    daveS:

    I’m still trying to understand what this is supposed to mean. Have any reputable physicists or philosophers spelled it out in greater detail than “v = dt/dt is nonsensical”, or “time is abstract, bruh”?

    It’s no more complicated than “v = dt/dt is nonsensical”. It means that changing time is self-referential. The simplicity of it all is so devastating to the physics community, they just ignore it and act as if Einstein’s time dimension is a fait accompli. As I said earlier, the physics community is gutless that way.
    By the way, “reputable physicists” has nothing to do with it. It’s a simple explanation that anybody can understand if they put their minds to it. I see you are one of those who must always have someone else do your thinking for you. That’s lame, man. You are condemned to believe in lies because our world is filled with lies. The more reputable they are, the bigger are their lies.

    “There is no problem of “the arrow of time.” There simply is no arrow of time, as if time could go one “way” rather than another. That metaphor is an unfortunate result of spatializing time. The picture of time as a line along which one might travel in one direction or the other is a conceptual disaster.”
    Source: “Time, c, and nonlocality: A glimpse beneath the surface?” Physics Essays, vol. 7, pp. 335-340, 1994 by Professor Joe Rosen

  5. 5
    mike1962 says:

    Time’s arrow is explained by the idea that the universe is a “virtual” reality, that is, an algorithmically implemented system.

  6. 6
    daveS says:

    Mapou,

    It’s no more complicated than “v = dt/dt is nonsensical”. It means that changing time is self-referential.

    v = dt/dt is totally sensical to me, but I think we’ve been over this before. Does anyone else agree with you, and have they published on this topic?

    The fact that dt/dt is self-referential in some sense also isn’t problematic to me. As an example, take a finite nonempty set S of real numbers. We can define the minimum of this set by:

    min(S) = the number x in S such that x is less than or equal to y for all y in S.

    which is self-referential.

    For another example, define x to be the real number such that x = (x^2 + 9)/6.

    Again, x is defined in terms of itself, so this is another case of self-reference.

  7. 7
    Mapou says:

    v = dt/dt is totally sensical to me

    Well, I tried.

    See ya around, daveS.

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