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Universe Has Many Alternative Histories Which Is

From: UFO UpDates - Toronto <ufoupdates.nul>
Date: Tue, 03 May 2005 09:37:51 -0400
Fwd Date: Tue, 03 May 2005 09:37:51 -0400
Subject: Universe Has Many Alternative Histories Which Is

Source: The Independant - London, UK


April 15, 2005

'The Universe Has Many Alternative Histories, But Which Is Real?'

Stephen Hawking

From a speech by the Lucasian Professor of Mathematics at
Cambridge University, to the Prince of Asturias Foundation in
Oviedo, Spain.

I am here to talk about Running History Backwards. We think of
history as a progression forward in time. One event causes
another, and so on. The principle of scientific determinism was
formulated by the French scientist the Marquis de Laplace in the
early 19th century. Given a knowledge of the state of the
universe at one time, the laws of science uniquely predict its
future evolution.

Scientific determinism also works backwards. Given the state of
the universe at one time, there is a unique previous history
that led to it. So why don't we tell history backwards? The
reason is that, because we usually don't have a complete
knowledge of the state of a system, we are more likely to be
able to predict its future evolution than its history.

The bottom-up approach to cosmology, in which one runs the
history of the universe forward in time, would be appropriate if
one knew that the universe was set going in a particular way in
the past. However, in the absence of such knowledge, it is
better to work from the top down, by tracing backwards from the
final state the histories that contribute to the sum over
histories. This means that the histories of the universe depend
on what is being measured, contrary to the usual idea that the
universe has an objective, observer-independent history.

What does it mean to say that the universe has many alternative
histories? Which is the real history of the universe? To answer
such profound philosophical questions, I think one must adopt
the positivist approach of Karl Popper and others. in this, a
theory is just a mathematical model to describe the
observations. It has no claim to reality, whatever that may be.
Two very different models may describe the same observations.
Both theories are equally valid, and neither can be said to be
more real than the other.

The results are disappointing for those who hoped that the
ultimate theory would predict everyday physics. We live in the
anthropically allowed region in which life is possible, but I
think we might have chosen a better location.

[Thanks to Stuart Miller of http://www.uforeview.net for the lead]

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