Comments on: At Least There Is Symmetry

By: Brian Koberlein

Brian Koberlein — Tue, 16 Jun 2015 12:12:33 +0000

That’s not remotely how it works. The Hubble telescope is in space and observes visible light all the time. The Solar and Heliospheric Observatory (SOHO) was specifically designed to observe the Sun from space, and it observes visible light.

By: Craig

Craig — Mon, 15 Jun 2015 21:23:35 +0000

Light emitted by stars like our sun IS NOT VISIBLE in space because it emits in extremely wave length like x-rays and Gamma. Light and heat from stars occurs ONCE IT ENTERS THE ATMOSPHERE where it is refracted into longer wave lengths. Therefore the universe is not of necessity millions of years old nor are he stars millions of light years away!

By: geckzilla

geckzilla — Sun, 14 Jun 2015 22:50:13 +0000

I can’t figure out if this is even knowable. There’s things you know you’ll never know, but this? I don’t know if I can’t know. It’s meta-unknowable.

By: Arturo Gutierrez

Arturo Gutierrez — Fri, 12 Jun 2015 16:50:57 +0000

I was under the impression that the direction of motion were entropy increases is always the “real” flow of time.
Or are photon’s abortion and emission perfectly efficient and no energy gets lost in the process?

By: Tim Spellman

Tim Spellman — Fri, 12 Jun 2015 16:44:19 +0000

I wish I knew more.

Was the big bang all energy, at least at first? How did the photons in the initial universe come to be? Were they created by emission?

If a photon is emitted and heads across a continuously expanding universe, I can imagine the universe expanding enough that the photon will eventually be alone in its part of the universe, with nothing to hit.

If a sufficiently energetic photon is absorbed by an electron, bringing that electron up two energy levels, can that electron decay in energy, and emit one photon for each of the two energy levels it decays? Can one absorption result in two emissions?

I wish I knew more.

By: Iacopo Papalini

Iacopo Papalini — Fri, 12 Jun 2015 04:47:20 +0000

What about entropy? In the billiard balls example we actually could know the real event from the reversed one because the impact is not perfectly elastic and some of the kinetic energy is transformed into heat, I.e. in the reversed version the entropy decreases so we can tell it from the ‘real’ one in which the entropy increases. I suppose this does not hold true in particle interactions?

By: Amir

Amir — Thu, 11 Jun 2015 20:30:08 +0000

All of physics can be cast in terms of initial conditions and interactions; or in “invariant action” terms of initial and final conditions. In the latter formulation, the entire path of events between the start- and end-points is a consequence of both of them equally.

This idea is central in SF piece “Story of Your Life” by Ted Chiang.

By: Alan

Alan — Thu, 11 Jun 2015 19:54:53 +0000

Mind blown.