Ok, now that the weather has been nice and cool in the evenings, nature has seen fit to cloud over the sky and deliver off and on rain for the last 10 days. Go figure that. At anyrate, all this "me time" has allowed me to finally crack open a book I’d been pining to read for sometime…
For sometime I’ve had questions and ideas mulling around in my brain regarding the nature of the universe based on bits and pieces of information gleaned from various sources (primarily Sky & Telescope, Scientific American and the like). Most of the magazine material I’ve read simply deals with emerging ideas of specific aspects of specific theories. So not having ANY formal education in cosmology or quantum physics myself, I was thinking things like, "Well why not this?" and "If that’s true then how come this?" I know just enough to be dangerous (read follow along), but far too little to participate intellectually and or make any conclusions on my own. Let me give you an example of one of the naive notions that had been bothering me.
We all accept that the universe is expanding in that everything is moving away from everything else (let me go on for a minute here). If that were the case, shouldn’t it follow that the spaces between the atoms and molecules that constitute my body are expanding as well? So how can we possibly detect expansion when the fundamental units (in this instance space/time) are expanding along with us? Let me try and illustrate this.
Imagine yourself in a windowless white room, perfectly square and floating in space. Now we’re gonna sprinkle some pixie dust and this is going to cause the room (and you the resident… um… nude geonaut) to expand in size by a factor of 50. At the end of the experiment you are asked to describe any changes you noticed during your time in the box. As far as you can tell, nothing happened. The box grew, you grew… but without any outside referrence or gravity/orientation/clothing cues, things appear to be exactly the same. By your observation nothing has happened. So you come outside to join the team for a coffee only to discover you are now 300 feet tall!
Now on the surface this sounds a reasonable conclusion does it not? If we are in a universe that is uniformly expanding on all scales this should be true. Of course I know its obviously not that simple, or else it would be. Some of things that I thought to consider were:
- When referring to the expansion of the universe, is it space-time that is actually expanding or is space-time a subset of a larger universe container which is expanding (multiple dimensions?).
- Is expansion adding volume on all scales (from the quantum domain up to large scale structures like galaxy superclusters)?
- Is expansion happening uniformly across these different structures?
- What role does/can gravity (as a weak force) play in the expansion of the universe?
- Is gravity a feature (subset) of space-time contained therein or is it a player on the field with space-time influencing cosmic expansion?
Ok, I’m beginning to confuse myself here (yes I probably have far too much spare time on my hands). Needless to say my thought experiment fails in the "real universe." Come to find out, the rate (velocity) of expansion of the universe is in fact retarded locally around large scale structures like galaxy clusters. Down on the level of say a planet, a personâ€¦ a bosonâ€¦ gravity is pretty much irrelevant. We live in an expanding universe filled with all kinds of forces that influence the expansion differently on different scales; strong, weak, electromagnetic, gravitationalâ€¦ sounds like there could be some kind ofâ€¦ unifiedâ€¦field? â€¦theory? in all this. I’m kidding. I wouldn’t even presume to go anywhere near that.
My point is The Whole Shebang: A State-of-the-Universe(s) Report by Timothy Ferris â€“â€“ excellent read! The author is able to take dry scientific information and present it in an easy-to-grasp, understandable and interesting text. So if you’re at all interested in finding out the difference between a WIMP and a MACHO, or examining the finer points of Supersymmetry and String Theory, or just curious as to whether or not non-baryonic matter really makes up 90% of the universeâ€¦ grab this book.
Hoping for clear skies soon! â€¦but I digress.