a mind-expanding universe

I was wandering and wondering about the Cosmos (as one does) when a question up and bit me. So I decided to ask Professor Paul Davies, the world-renowned theoretical physicist and cosmologist. The Prof has very broad interests extending from the “highly mathematical to the deeply philosophical.” He likes “…to ponder the big questions of existence: How did the universe begin? What is the destiny of mankind? Is there a meaning to the universe?”

As a great fan of Professor Davies’ work, and an avid reader of his books and articles, I was very grateful and appreciative that he took the time to respond to me quickly and curteously. Below is the gist of our email correspondence in late 2006:

SRS: In our expanding universe, space itself is expanding. The analogy of inflating a balloon is sometimes given. But if space itself is expanding, then how about the stuff that occupies space? Are space, and the stuff that occupies space one and the same thing? Is matter the same thing as space, what about spacetime?

If space is expanding and the stuff that occupies space is expanding, then is it true to say that all the superclusters, clusters, galaxies, stars, nebulae, dust and planets in the universe are also expanding? And the atomic and sub-atomic particles, are they also expanding? And the space between them at the sub-atomic level?

And as space expands, do human beings expand? How about our eyes, ears, hands? And the particles making up our eyes, ears and hands? And the space between the particles? And our telescopes and detectors and other pieces of equipment for observing the expansion of the universe? And the atomic and sub-atomic particles comprising the equipment?

If everything is expanding (presumably at the same rate) then how would we notice? Red shift / Doppler effect? But wouldn't relativity mean that if everything is expanding then nothing is expanding , and nobody would be able to tell the difference?

PD: The space between galaxies expands, but the galaxies themselves don't. Nor does anything else. It's all explained in my new book The Goldilocks Enigma.

SRS: A follow up question: If outside the galaxies space is expanding and inside it is not, where do you draw the line? There are no sharp edged boundaries in or outside galaxies.

PD: There is no boundary. Systems that are gravitationally bound do not expand. Those that are unbound do. It is a straightforward calculation to determine how bound systems shade into expanding ones. It is somewhere around the size of a cluster of galaxies, depending on the exact mass and velocity profiles, and the amount and degree of clustering of dark matter. These things are routinely modelled on supercomputers.

Copyright © S R Schwarz 2007. All rights reserved.

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