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The Question
(Submitted March 08, 1998)
My question: On PBS, an astrophysicist commented that other universes might
have different physics and natural laws. Is this possible and what are some
differences that there might be? I think that the formulas used to determine
properties might just be different depending on the amount of matter in the
universe, but what do the REAL astrophysicists think?
The Answer
There are a handful of constants that shape physics. The three
main fundamental constants that we measure but at this point cannot be
determined are:
c - this is the speed of light, it is important in electricity,
magnetism and the conversion of matter to energy.
h - this is Planck's constant, it is important in atomic and
nuclear physics
G - this is the universe gravitational constant, it holds
planets in their orbits and determines the large scale
structure of the universe.
We have no theory of why the values of c, h, and G are what they are.
This begs the question of why they have the values they do,
and what the universe might have looked like were they (and
other constants like the mass of an electron) different. It
turns out you can't change these values much without making
life-as-we-know-it impossible. Such consideration has led to
several variations of "Anthropic Principle."
These constants reflect fundamental characteristics of space and the
quantum mechanical vacuum. In the General Theory of Relativity, for
example, G represents the response of space to mass, and therefore is
intimately connected with the fabric of space. While G reflects
the global, large-scale character of space, Planck's constant, h, reflects
the nature of space on atomic scales as it is expressed in the parameters
characterizing subatomic particles and photons (energy levels, angular
momentum, linear momentum) and the waves associated with matter. The speed
of light in a vacuum, c, is the limiting velocity of matter through space
and the characteristic velocity of energy through space, and thus
reflects, on the one hand, the resistance of space to acceleration (the
drag of the vacuum), and, on the other hand, the density of the vacuum, in
the same sense that the speed of sound reflects the density of the medium
through which acoustical waves travel.
In short, the only way these constants could really be different would be
if the characteristics of space were different. I've addressed space and
not time here, but it is likely that, based on the same theories mentioned
above, the fundamental nature of the time component of spacetime would
have to be different if these constants were different. Since spacetime
and matter-energy come to us together courtesy of the Big Bang and are in
some fundamental sense inseparable, we can assume that G, h, and c could
not be changed without re-engineering the birth of the universe which, if
you buy the theories that point to near-critical density of matter-energy
in the universe, all indicate that space, time, matter, and energy as we
know them are inseparable from the three fundamental constants that
characterize them. Although we cannot, at this point, alter these constants,
one might wonder about how our universe would be different if these
values were changed.
Jeff Silvis and Mark Kowitt
For Ask an Astrophysicist
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