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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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