Letter: Probably not

From Ewan McLeish, University of Reading

Max Tegmark’s theory that all possible universes exist
(“Anything goes”, 6 June, p 26)
is intriguing, but it seems to buck basic ideas about the nature of
probability.

Tegmark argues that the only universes that will be “perceived” are the ones
containing life, and that since the likelihood of life arising is spectacularly
small, countless other universes incapable of supporting life must also have
arisen. However, Tegmark is arguing from a post-event perspective from which the
event does indeed look remarkable.

Take, for example, a crash involving two vehicles. Looking back on the
accident, the series of events that led to the crash seem to be an incredible
series of coincidences and bizarre twists of fate which would be impossible to
predict. Suppose one of the drivers had started out a minute earlier, or that a
set of traffic lights had changed slightly later, or that one of the drivers had
taken a different route. In any of these events, and a million others, the
accident would not have happened. And yet the mangled wreckage tells us
emphatically that it did.

Furthermore, the probability that the accident is/was going to occur changes
with the proximity to the event itself. A week before the event the chances of
it happening are virtually nil, but a split second before, the chances of a
collision are very high indeed. In other words, the probability of a particular
event occurring is not static but changes with time.

When we view an event such as the origin of life in the Universe, we can
indeed marvel that conditions were so suited to such an event occurring. But, as
Tegmark himself argues, we are only able to perceive the event precisely because
life has arisen in the Universe. In our retrospective view, the event, like the
car accident, has become a certainty arising out of what were once seemingly
impossible odds. This, in itself, does not make it remarkable, or argue for
other parallel universes in which different physical laws operate. It merely
confirms that a series of events took place, and that one of the results was a
life form that could reflect on it in the pages of New Scientist.