**Paul Dirac in Florida**(thanks to Laurent Sacco!):

Now, the main topic:

If you haven't heard, Sean Carroll appeared on the Colbert Report, a very entertaining left-wing emulation of the O'Reilly Factor that runs on Comedy Central TV. He promoted his dumb book, "From Eternity To Here".

Full video segment (after adds, Carroll appears around 16:25)Colbert began with a good question: why do we need a theory of time? Carroll answered that it's because we can't answer some questions about time. Colbert can answer any questions so he wanted examples. Carroll asked Colbert why the past is different from the future.

Because we're not there anymore.Yes: even Carroll had to admit that Colbert did know the difference. :-) So he asked almost the same question once again: but what is the difference between these two things?

In the future, I will have gained weight.Carroll said it was the right answer but he said that we don't know why the Universe has the feature that people gain weight. This is, of course, a complete rubbish - the same rubbish that penetrates Carroll's reasoning about all these matters. Whether Stephen Colbert gains weight is determined by the physics of Stephen Colbert. It has nothing whatsoever to do with the Universe, nothing whatsoever to do with cosmology.

They discussed Benjamin Button, a semi-time-reversed movie with Brad Pitt.

When Carroll says that the Universe started "very very organized", Colbert suggested that he thought that it was chaotic at the beginning. And of course, he has a good point. The organized structures - e.g. life forms - didn't exist. And the entropy density was much higher in the past (but the total volume was much smaller, so that the product was smaller, too). It's very problematic to identify the notion of a "lower total entropy" with the adjective "very very organized".

As Colbert says, it's like saying that "butter is more organized than cake". Of course, Carroll couldn't manage to explain why "it's really so", especially if it's obviously not so given any sensible definition of "organization".

Fine. So Colbert asks why did the Universe get more organized or disorganized with time. And Carroll says that we don't know. Colbert is rightfully shocked. We don't know? What's the point of science then? What have scientists been doing all the time?

Needless to say, Colbert is absolutely right. If people couldn't answer similar basic, trivial questions, the achievements of science would be zero. We wouldn't even start to touch the basic properties of the reality.

The matter of fact is that we have understood these things at a superficial, macroscopic level for millennia and we have known the right microscopic explanations of all these issues for more than a century. Only Sean Carroll hasn't understood them because he has no idea about statistical physics and thermodynamics.

When it comes to any of these issues, he is just a completely deluded amateur.

Colbert even understood one more point, so he correctly asked: what do these philosophical questions have to do with light, gravity, relativity, and all these technical things in modern physics? Of course, the correct answer is Nothing.

The second law of thermodynamics holds completely universally and the related basic features of the world such as the arrow of time have nothing to do with the Lagrangian of electrodynamics or general relativity. The arrow of time exists in the context of any dynamical system, whether it is influenced by the electromagnetic, gravitational, or other forces (or no forces).

Carroll says that the link stems from the fact that relativity implies that space and time are the same thing which is why the future and past should be as symmetric as the left and right side.

However, this is clearly another piece of bullshit. When one actually looks at the geometry of spacetime, as determined by special relativity, he will find out that the directions in the Minkowski spacetime can be either spacelike or timelike. While the set of spacelike directions in our 3+1-dimensional spacetime is connected, the set of timelike directions has two components - the future-directed timelike vectors and the past-directed timelike vectors (inside the light cones).

It's just not true that relativity - or its basic symmetry, the Lorentz symmetry - implies that there must be no difference between the future and the past.

At the end, they defined what the multiverse is and whether Colbert's show airs before Jon Stewart in other universes.

At any rate, Sean Carroll has tried to convince Stephen Colbert about many things in which his understanding is much poorer than the understanding of Stephen Colbert. I am kind of stunned by his visual self-confidence.

He must have learned by now that everything he is saying about these matters is pure crap.

Entropy within a volume of spacetime is an invariant, independent of the motion of an observer. In fact that, pure number (counting), the action (or more properly, the action integral) are the only physical invariants, and independent of the coordinate system employed, because the Jacobian of any transformation is invariant.

ReplyDeleteOn the other hand, the entropy DENSITY (entropy per "volume" of spacetime, defined by INTEGRAL (dx_i)) is not an invariant. Thus he is referring to a quantity that has no general significance.