23 thoughts on “Time the Destroyer”

  2. James

    What’s the smoothness measure he’s referring to when he says the universe is much smoother than a black hole?

  3. John Preskill

    I believe that if your showed me two one-minute segments of this talk, chosen randomly, I would be able to guess which segment came first with reasonably high success probability.

    Is that because the talk is self-destructing?

  4. Sean Carroll

    James — it’s just the metric of space. Early on space is completely homogeneous, but as structure grows it becomes much lumpier. A black hole is as lumpy as you can get.

  6. Brett the destroyer

    I will bring your theories of entropy to the ground using your very own relativity theory! MWOO HA HA HA HA HA HA!

  9. James

    @Sean: Ah, sorry, I misheard him originally – I thought he was saying that a black hole is the MOST smooth thing we can imagine (which I interpreted as meaning the event horizon is very smooth, which itself is a bit of an iffy statement, and made no sense in the context of comparison to the universe), but he actually says least smooth. My mistake.

  11. Evan

    I was hoping he would touch on the idea that, if our mind’s perception of time is entirely based on the physical / chemical entropy-obeying properties of brain, then our perception of time is therefore not tied to some grand external Time which moves the universe from one moment to the next in a meaningful Present.

    Anyone who studies relativity knows this to be true, but I think it’s a pretty shocking revelation for those who aren’t as familiar. There is no such thing as a Present in which the universe moves from one moment to the next. If you want to be flippant, you can say Time doesn’t exist.

  12. Meh

    Evan @ #11

    I both do and don’t believe that time exists.

    I do believe time exists because change occurs. You could call the existence of change the dimension of Time, though that’s kind of confusing and someone should do something about that.

    I’m not going to say why I don’t believe it exists because it would make a good publication…that everyone would exile me for. But I gotta say, I kind of agree with Julian Barbour

  13. Steve

    He says the smoothness of the universe is being destroyed. But isn’t the universe evolving to a state of thermal equilibrium which would be smooth and homogenous?

  14. Alec

    John @ #3: In order to correctly time-sequence segments of the talk, the level of presentation would need to betray an increasing level of depth and/or sophistication. What’s being destroyed, then, is the level of ignorance of the audience — or perhaps more poetically, the domain of the unknown is suffering degradation.

  15. Phillip Helbig

    @13: No, because of gravity. The initial universe had a very low entropy, and it is evolving toward a higher entropy. The inital universe looks like it should have a high entropy, and perhaps look like it is evolving to a lower entropy. However, this neglects gravity. (Of course, evolution is from low to high entropy, not vice versa.)

  16. Sean Carroll

    Steve– The smoothness of the universe is being destroyed, temporarily. Later it will be restored, as galaxies move apart and black holes evaporate. There is no simple relationship between entropy and smoothness; it depends on the density. (High entropy = smooth only when density is low enough.)

  17. Brett

    As far as smoothness is concerned; I guess I always look at it as equilibrium of any sort being a certain type of smoothness. More evidence for “Time” being a dimension, the absence of smoothness is the existence of differentiation…Time. If every measurement of space was at an energy level of 500 GeV (like the pre-Big Bang singularity) and it never changed, that seems to be smooth in that there is no variation. But likewise, if it’s 1.3 X 10 ^-45 eV (darn (edit) near nothing in existence), the same smoothness. But back to Time as a dimension, it all depends on how energy is distributed like Sean is saying. The less variation there is, the smoother “existence” becomes. Which is why differential mathematics is the language of physics, but that’s how I see it; and I may see it incorrectly 🙂

  18. LaserGuy

    I was not aware that we had actually discovered the size of the universe – I was under the impression that it was either infinite, or some unfathomably large number?

    But then I noticed that, given that he expressed the value in kilometers, the stated size seemed suspiciously small? According to NASA, the distance just to one of the NEAREST superclusters (Coma) is 2.83×10^21 kilometers – is that distance really 1/35th the entire width of all of creation? I’m beginning to feel downright cramped!

    Converted to the more appropriate light-years, his claimed size makes even less sense. 10^23 kilometers is roughly 10.57 billion light years.

    But as even many of us amateur astronomers know, just the fraction of the total universe that is observable from here is about 93 billion light years across! And every study I have read to date states that the universe is either infinite, or if finite, has a minimum possible size MANY times larger than even the 93 billion light year portion we can observe.

    So how can the universe be only 10.47 billion light years across? Was there some new discovery that proves the universe to be a lot more cramped than everybody thought? Or did some cosmologist make a mistake of quite literally cosmic proportions? LOL!

  19. Phillip Helbig

    @18: He’s referring to the size of the observable universe.

    We don’t know the size of the universe. Current observations imply that it is either infinite or finite but very big.

  23. Faizan sarwar

    Time is always related to matter,and it has a constant behaviour which depends upon mass.So,if matter is destroyer or creater than time will be.
    And, anything else is only human mind understanding.

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