SoylentNews is people
SoylentNews
From WIRED, again. Sometimes they have good stuff.
In the early 1970s, people studying general relativity, our modern theory of gravity, noticed rough similarities between the properties of black holes and the laws of thermodynamics. Stephen Hawking proved that the area of a black hole's event horizon—the surface that marks its boundary—cannot decrease. That sounded suspiciously like the second law of thermodynamics, which says entropy—a measure of disorder—cannot decrease.
Yet at the time, Hawking and others emphasized that the laws of black holes only looked like thermodynamics on paper; they did not actually relate to thermodynamic concepts like temperature or entropy.
Then in quick succession, a pair of brilliant results—one by Hawking himself—suggested that the equations governing black holes were in fact actual expressions of the thermodynamic laws applied to black holes. In 1972, Jacob Bekenstein argued that a black hole's surface area was proportional to its entropy, and thus the second law similarity was a true identity. And in 1974, Hawking found that black holes appear to emit radiation—what we now call Hawking radiation—and this radiation would have exactly the same "temperature" in the thermodynamic analogy.
[...] But what if the connection between the two really is little more than a rough analogy, with little physical reality? What would that mean for the past decades of work in string theory, loop quantum gravity, and beyond? Craig Callender, a philosopher of science at the University of California, San Diego, argues that the notorious laws of black hole thermodynamics may be nothing more than a useful analogy stretched too far.
After what Hawking said about philosophy, I think that astrophysicists need a bit more perspective.
(Score: 2) by melikamp on Thursday September 12 2019, @11:24PM (1 child)
Can you please point to a precise (mathematical) definition of the entropy of a physical system, either classical or quantum or relativistic?
Can you please also point to an effective procedure to measure what you defined above. If such procedure is not currently feasible, it should still be theoretically feasible to carry out in the future, with better instruments.
This is a question for everyone, and I am really curious. I have a deep-seated suspicion that most people, even physicists, do not have a clear (mathematical) idea of what entropy is.
(Score: 2) by ikanreed on Friday September 13 2019, @02:10AM
I'm most familiar with it in the context of chemistry. This is a very limited context because it only really describes the entropy of gasses in terms of particle motion, but such descriptions are usually much easier to fully grok than some 30 million variable universal formula.
dU = T*dS - p*dV
U Interrnal Energy
T Temperature
S Entropy
p Pressure
V volume
Now, that looks like a hellacious differential equation to solve generally for real world scenarios, but it's quite intuitive to visualize. As your "perfect environment containment box" expands in volume, if your energy and temperature and pressure remains constant, entropy goes up proportionately. The particles have more possible states that they're then scattering into as those physical spaces become available to fly into.