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Does light have an infinite lifetime?

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Re: Does light have an infinite lifetime?

#51

Post by xyzelement »

ClarityJones wrote: post #31
pc86 wrote: post #22

Earlier quoted context omitted.

Do you have something constructive to add related to the content of the article or are we just quoting random bible verses on HN for no reason?

It wasn't exactly random. The topic of the article is that light is eternal, and the commenter shared a quote from over a thousand years ago stating the same thing. So, the idea of light having an infinite lifetime is apparently not new... even if the mechanics of light are better understood these days.

This is in line for me with the moment of "creation." For most of the history of science as a thing, the scientific view held that the universe was infinitely old cosmos without a beginning or end. The greek model. It was only in 1900s that big bang was theorized (by a catholic priest) that science now views that there was a moment before which the universe didn't exist and after which it did.

The fact that someone reading Genesis would have had a more accurate conception of the origin of the universe, prior to big bang becoming popularized very recently in the grand scheme of things is noteworthy.

Re: Does light have an infinite lifetime?

#52

Post by doodlebugging »

westmeal wrote: post #48
doodlebugging wrote: post #43

Earlier quoted context omitted.

I believe they're right about there being only one single electron. I tried to start my Pathfinder yesterday and it was dead as a doornail. None of the dash lights lit and there was not even a click from the starter. Someone else must've been using that electron though since I tried again a few minutes later and it cranked right up. I had my turn with it so I'm not mad at all.

Um maybe check your battery terminals for corrosion :)

I covered all those bases. I'm not 100% sure what happened but when I initially tried to start the vehicle I had it connected to a solar battery maintainer in full sunlight. It should've had bazillions of photons sacrificing part of themselves to be stored electrons but instead I got nothing. After disconnecting that from the battery and testing all the fuses I made another attempt to start it up and it worked fine. It's possible that the voltage output of the panel swamped the voltage expected by the ECU and it refused to energize to save the system from electrical damage by overvoltage.

Or maybe that single electron hadn't quite made it to my battery on my first attempt. That's one busy e.

Re: Does light have an infinite lifetime?

#53

Post by westmeal »

doodlebugging wrote: post #52
westmeal wrote: post #48

Earlier quoted context omitted.

Um maybe check your battery terminals for corrosion :)

I covered all those bases. I'm not 100% sure what happened but when I initially tried to start the vehicle I had it connected to a solar battery maintainer in full sunlight. It should've had bazillions of photons sacrificing part of themselves to be stored electrons but instead I got nothing. After disconnecting that from the battery and testing all the fuses I made another attempt to start it up and it worked fine.…

I find pouring electrons into a funnel usually helps by avoiding an electron spill all over your battery. Glad it works tho!

Re: Does light have an infinite lifetime?

#54

Post by wizzwizz4 »

doodlebugging wrote: post #49
AgentME wrote: post #46

Earlier quoted context omitted.

Electrons aren't unique in not having identities. Photons of the same wavelength are similarly fungible if I remember right, though it's a little more defensible to call the reflected light not the same photons since the original photons are transformed to something we don't call photons before photons are produced again.

But at a reflection event you aren't producing a new photon, you are only reflecting a portion of the original determined by the refractive indices of the reflection interface. At that interface, part of the original photon is reflected and the rest is transmitted across the interface as a new photon and both have a modified bandwidth relative to the parent photon. So the one you see reflected is the same photon afte…

That would imply a frequency shift, which clearly doesn't happen (mirrors don't redshift the light that hits them).

Re: Does light have an infinite lifetime?

#55

Post by [deleted] »

colechristensen wrote: post #3

Huh? Light has zero lifetime, along with all massless particles. When you travel at c your clock doesn’t tick. From the viewpoint of a photon it is emitted and absorbed at the same instant. You cannot decay if you don’t experience time. I’m not sure exactly how index of refraction works with this.

[deleted]

Re: Does light have an infinite lifetime?

#56

Post by lolc »

doodlebugging wrote: post #47
adonovan wrote: post #38

Earlier quoted context omitted.

Feynmann is very clear that the photons bouncing off a mirror are not the same ones that hit it. They are absorbed by electric oscillators (free electrons in the material) and destroyed; then new ones are created and emitted. He's also careful enough to point out that electrons don't really have an identity that would allow you to meaningfully define "not the same". :)

I wonder about the all the photons lost in fiber optic installations. What happens to them in their short lives? There must be a creation and an extinction event. A photon jumps into the glass fiber and travels until it encounters an opto-electric coupler where the photon craps out and is converted to an energized stream of electrons, or maybe it borrows the only real electron in the universe for an instant as it fli…

My understanding is that photons don't have a life the way we do. They move at the speed of light and thus time does not advance for them. They cannot change between emission and absorption, no matter the distance. Always bends my mind to think about it.

Re: Does light have an infinite lifetime?

#57

Post by DennisP »

doodlebugging wrote: post #37

Where do the photons that hit my retina go when I finish with them? If they have infinite lifetimes then does each one carry a memory of it's creation event? When I burn a log in my fireplace and a cinder flares and pops creating a spark, does the photon exist after the spark energy flares out and the cinder is no longer illuminated enough to be detected by my eyes? If photons are infinite then harvesting light would…

If you haven't yet, you should definitely read the famous little scifi story Light of Other Days.

Full text: https://www.physics.utoronto.ca/~jharlow/slowglass.htm

Re: Does light have an infinite lifetime?

#58

Post by rvbissell »

lolc wrote: post #56
doodlebugging wrote: post #47

Earlier quoted context omitted.

I wonder about the all the photons lost in fiber optic installations. What happens to them in their short lives? There must be a creation and an extinction event. A photon jumps into the glass fiber and travels until it encounters an opto-electric coupler where the photon craps out and is converted to an energized stream of electrons, or maybe it borrows the only real electron in the universe for an instant as it fli…

My understanding is that photons don't have a life the way we do. They move at the speed of light and thus time does not advance for them. They cannot change between emission and absorption, no matter the distance. Always bends my mind to think about it.

> They move at the speed of light and thus time does not advance for them.

Isn't it more accurate to say that photons move at the speed of causality, when the medium is a pure vacuum? Because in some other medium like glass, the speed of light is slower than the speed of causality.

So my follow-up question is: do slower photons (such as those propagating through a fiber-optic strand, or water) then experience the advancement of time?

Re: Does light have an infinite lifetime?

#59

Post by Kranar »

lolc wrote: post #56
doodlebugging wrote: post #47

Earlier quoted context omitted.

I wonder about the all the photons lost in fiber optic installations. What happens to them in their short lives? There must be a creation and an extinction event. A photon jumps into the glass fiber and travels until it encounters an opto-electric coupler where the photon craps out and is converted to an energized stream of electrons, or maybe it borrows the only real electron in the universe for an instant as it fli…

My understanding is that photons don't have a life the way we do. They move at the speed of light and thus time does not advance for them. They cannot change between emission and absorption, no matter the distance. Always bends my mind to think about it.

Almost everything you said is correct. Photons do not have a reference frame, so time does not advance because for a photon there is no time coordinate system in the first place. It's not simply that photons don't experience time, it's that time and space don't exist for photons.

>They cannot change between emission and absorption, no matter the distance.

From the point of view of a photon, neither time or space exist. They have no reference frame at all. However, from an outside frame of reference that is travelling less than the speed of light, photons do change for example they get red shifted as they move through stronger gravitational fields.

Re: Does light have an infinite lifetime?

#60

Post by Kranar »

prettydeep wrote: post #34
gwern wrote: post #2

Interesting. I had no idea that the universe would eventually be basically just photons. I wonder if that is why Stephen Baxter had his 'photino birds' as the final form of life in his Xeeleverse?

Roger Penrose has a theory about a cyclical conformal universe, which requires that the universe eventually only contains photons. As photons travel at the speed of light, they do not experience the passage of time, so they also do not experience distance (space). So in the deep remote future, when only photons are left, the difference between the very large and miniscule disappears, and you get all photons in the un…

This is some absolutely crazy idea. I mean I'm in no position to analyze it critically but that is pretty mind blowing.
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