Monday, October 08, 2007

Quantum randomness

I'm in a New Scientist article entitled Universe explained by quantum randomness. I can't access the entire thing, since I don't have a New Scientist subscription, but I've pasted the free-access part of the article below.

The article is based on observations made in this paper, where...

...I discuss a rather strong implication of quantum mechanics. Simple entropic or information theoretic arguments, together with standard big bang cosmology, imply that essentially all the detailed aspects of the world around us (the arrangement of galaxies in clusters, electrons in stars, leaves on trees, or books on bookshelves) are random consequences of quantum outcomes. There is simply not enough information in the initial conditions to specify all of these things. Unless their variability is illusory, it must result from quantum randomness. Very little about the universe today is predictable, even with perfect knowledge of the initial conditions and subsequent dynamical evolution.

Universe explained by quantum randomness
08 October 2007
Marcus Chown
Magazine issue 2624

Look around you - at the sun in the sky, a tree swaying in the breeze, a woman walking her dog down your street. You may think all these things have a cause. Einstein did. He hated the idea of quantum randomness underlying everything, which is why he declared, "God does not play dice".

Tough, says Stephen Hsu of the University of Oregon in Eugene. "Not only does God play dice with the universe but, if he did not, the complex universe we see around us would not exist at all. We owe everything to randomness."

Hsu came to his startling conclusion by comparing the amount of information in today's universe with that in the first moments of creation. According to standard cosmology, the universe grew enormously in the first split second of its existence, blowing up from a tiny patch of vacuum. "Because the patch was exponentially smaller ...


Anonymous said...

"Hsu came to his startling conclusion by comparing the amount of information in today's universe with that in the first moments of creation."


If that means you believe -- as I do -- that there is more information now than at the beginning, can you help me explain to people that entropy has decreased in the observable universe since the beginning. And that we have no evidence that it is increasing even now?


Steve Hsu said...

This is a technical point, but the answer is that only coarse grained entropy increases with time.

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