Andrew Testa
Second Unit
- Joined
- Mar 22, 2002
- Messages
- 263
Getting lost at page 5. The theories regarding entropy within a black hole seem to be making some assumptions that I'm not entirely comfortable with either, although that's probably an artifact of my understanding, or rather lack thereof.Trying to imaging alternate spacetimes is confusing, if that's what you're getting lost on. Here's a quick analogy, not really correct, but it points out the overview. Since we're all somewhat audio folks around here ('else why be reading HTF), let's examine measurements of an audio signal. We can graph it in the time domain, that is plot dB vs. time, or we can graph it in the frequency domain, plotting dB vs. frequency.
In the first, time and signal strength are 2 dimensions that sound can exist in. We can formulate theories on how sound behaves over time based on it. In the second, frequency and signal strength are 2 dimensions that sound can exist in. We can formulate theories about how sound behaves over frequency ranges based on it. Each attempts to explain the behavior of sound, but they use different dimensions to do so. formulas for time based sound are different from formulas for frequency based sound. Some aspects of sound are better described in one vs. the other. For example, a time domain measurement doesn't give you any information about whether that 6 dB spike was at 10Hz or 3000 Hz.
These different sound domains can be thought of as different spacetimes. They all attempt to describe the physical universe, but they make different assumptions about the nature of the dimensions their formulas describe. Their goal is to find a set of initial conditions that lead to physical behavior similar to what we see, but trying alternate approaches that can explain things that can't be explained by using our accepted 4D (3D + Time) spacetime. Frequently that involves postulating multiple dimensions or bizarre mathematical descriptions of basic particles. But what they are basically doing is trying alternate formulas to describe the universe. Those sets of formulas are collectively called a spacetime, since they try to describe all of space and time as we see it.
BrianW, does this work as an analogy?
As far as the entropy, don't worry. Black hole thermodynamics is truly the stuff at the bottom of the rabbit hole. There's no common sense to it, and it makes people like me need a dose of South Park to clear the head. I once tried reading one of Kip Thorne's books on black holes, and when he got to the effects of spinning, charged black holes (still in chapter one) I suddenly became illiterate.
Andy