Moondust & The Physics Of Time

The evidence.

what makes you sure that the Big Bang ever existed?

Polar Per

It did help! I get it now. Thanks!

This won’t help, but it might entertain https://youtube.com/watch?v=j5Ths1bpQdQ&si=EnSIkaIECMiOmarE

Rad Antonov

Another issue with entropy: As posted by Rad under my initial post, S = Q/T, entropy is very small at the very high temperature at the Big Bang, S tends to 0. However, it would be infinite, S tends to infinity at T = 0, after the 'heat death' of the universe when T will be 0 degrees K, everything is at the energy ground state. I don't understand thermodynamics and this entropy thing because it is not intuitive. I need help, like a new born baby.

What I find interesting is his New York accent. I haven't read his lectures in a while, so I may as well read those books again. I bet I'll still have no luck with thermo though.

Hear you on the thermo/stat mech. Not intuitive. He has some things to say about entropy in Chapter 44, maybe that helps. We have come a long way indeed. Not only are they free to access now but you can hear the lectures as they were delivered. Listening to Feynman talk about physics is a visceral experience I can never get enough of. That debate with a grad student or could even be another faculty member was sooo good.

Rad Antonov

Rad, Happy Thursday! Very interesting stuff. I just don't get entropy, from that lecture: "Order is not order in the sense that we like the arrangement, but in the sense that the number of different ways we can hook it up, and still have it look the same from the outside, is relatively restricted." I read a book by a physicist, British I believe, who argued that entropy hadn't increased, but decreased as where we once had plasma, we now have order in the form of planets, stars, etc. This doesn't seem to correlate with what Feynman says, which seems to me to be that absolute disorder, from S=Q/T, is actually low entropy. I gave up on thermodynamics because of ideas like that, not intuitive at all to me. I have my issues. I looked the book up in my borrowed records from my library and it wasn't there, so I can't tell you its title. I was hoping to have it as a reference. Maybe later. One more thing. My mom bought me the Feynman Lectures on Physics paperback book set when I was in high school in the 70s and it wasn't cheap. Now I see that it's all online for free! I won't tell my mom.

Because the temperature was near infinite, so by the thermodynamic definition, S=Q/T, the entropy was infinitesimally small for any finite amount of heat sloshing around. This of course is a gross oversimplification and hardly intuitive. I am just reciting a definition, which doesn’t necessarily correspond to an intuitive understanding. In fact, this topic leads to one of the most heated exchanges in the Feynman lectures: https://www.feynmanlectures.caltech.edu/I_46.html. Listen to the audio starting at the 56 minute mark. Section 46-5 at the end of the chapter provides the context. Keep in mind that this was recorded in 1962. That’s two years before the CMB was detected! The idea of a single point of origin and expansion of the universe had been percolating but it was hardly established science. Feynman once again does a fantastic job teaching the audience how to think like a physicist. He was a master of the subject and seemed to have thought about every possible problem!

Rad Antonov

IMO, the problem is that too many people think that we can tech our way out of the problems that tech and human nature got us into. They ignore the human nature part of the cause in their proposed solution.

Tracey, Happy Thursday! I understand why physicists try to explain time's arrow with entropy, but it very well could be that time is fundamental, that it only progresses into the future, regardless of what math implies. Math is after all, only a tool for modeling reality and therefore if time is fundamental and only progresses into the future then the mathematical model needs to change to reflect reality. IMO, this may be one of those 'lost in math' situations.

I think the reason that physicists try to explain why time has a direction is because all of our favorite equations are time reversible. So, what breaks the symmetry and causes time to only flow in one apparent direction -- entropy. If we lived in a universe in which time's arrow was intrinsically one-sided (no "cause"), then the equations that we discovered that describe the universe should have an intrinsic one-sidedness time direction as well. Or, at least, that's my read on the situation.

I am not sure how many MDs adhere to it, but the idea of "do no harm" seems to be one that is universally applicable.

D Brown

Regarding time's arrow, why couldn't it simply be that time does in fact only flow forward? Why is entropy seen as being necessary if forward time is reality? Regarding entropy, why is entropy 'small' in the plasma of the Big Bang and 'larger' when matter coalesces later? I've always had trouble understanding thermodynamics, among other things.

I think that the moondust idea is too smart by half. Trying to band-aid over the business as usual that caused the problem is no solution. We aren't going to fix global warming by 'engineering' a solution except by developing the integral fast reactor to commercial scale and then using its capacity to start the hydrogen era. Oh, and perhaps sequestering some of that carbon, reducing human population, replacing our extractive economy with a sustainable one, etc.

The Lagrange Moon Dust idea sounds pretty cool but also potentially hazardous to future astronomy instruments as well as being a great name for an experimental ambient noise music album.