Friday, July 27, 2012

Many-worlds skepticism needed

Skeptic Michael Shermer writes:
Why is there something rather than nothing? The question is usually posed by Christian apologists as a rhetorical argument meant to pose as the drop-dead killer case for God that no scientist can possibly answer. Those days are over. Even though scientists are not in agreement on a final answer to the now non-rhetorical question, they are edging closer to providing logical and even potentially empirically testable hypotheses to account for the universe. ...

According to the “many worlds” interpretation of quantum mechanics, there are an infinite number of universes in which every possible outcome of every possible choice that has ever been available, or will be available, has happened in one of those universes. This many-worlds multiverse is grounded in the bizarre findings of the famous “double-slit” experiment, in which light is passed through two slits and forms an interference pattern of waves on a back surface ...

Carroll then cautioned: “Obviously the entire set of ideas is controversial and speculative, and should be presented as such, but it’s taken very seriously by a large number of extremely smart and respectable people.” For example: Leonard Susskind, Alex Vilenkin and Alan Guth (on the pro-multiverse side) and David Gross, Paul Steinhardt, and Edward Farhi (skeptical of the multiverse side).
No, the many-worlds multiverse is not grounded in the double-slit experiment. That experiment is not bizarre at all, if you believe in the wave nature of light (or electrons).

Instead of just saying that some light goes thru each slit, many-worlds says that the light goes thru differenct universes. Because the light could have gone thru either slit in the past, many-worlds says that the light is split into different universes in the future. The theory is bizarre and does not explain the simplest experiments.

Many-worlds says that all possibilities happen in alternate universes. That deflates the predictive power of quantum mechanics. It is hard to say that an experiment is contrary to theory, because we might be in the alternate universe where the improbable happens.

The belief in many-worlds is largely based on a belief in a certain sort of time symmetry called unitarity. People argue that if there are multiple possibilities for events in the past, then there should be multiple possibilities in the future. In the case of the double-slit, the two slits are not just possibilities, but understanding the interference requires that the light really goes thru both slits. So the many-worlds advocates make the leap to saying that future possibilities must really happen also, even if in alternate universes.

Shermer points to smart people instead of giving evidence, and uses this as an example of how science is better than religion. That is foolish. There are plenty of smart people who believe in religion also.


  1. "but it’s taken very seriously by a large number of extremely smart and respectable people."

    As a non-physicist, I tend to feel than many physicists working on these exotic issues have cut themselves adrift from a reality of observable phenomena.

    Speculation is good, but it surely doesn't become science until tied down to observable phenomena.

  2. Yeah, that quote stood out to me. I was surprised that a professional skeptic would accept such a weak line.