How long do neutrons live? Physicists close in on decades-old puzzle
nature.com
nature.com
"according to the photons frame of reference, Heeck found that its lifetime would be a rather short three years; however, from our frame of reference, light would live about one billion billion (10^18) years"
https://futurism.com/science-explained-long-can-photons-live...
No, the concept of "time passing" for an object moving at the speed of light has no meaning. That's why "lifetime" has no meaning for a photon if it has zero mass.
Or, to put it another way, the speed of light is where time dilation and length contraction run into each other and it all goes zero-divided-by-zero.
You're using a different notion of "time passing". Yes, we, observing photons, certainly observe them to take a finite time to cover a finite distance. But that is not the same as the concept of "time passing" for the photons themselves, for example according to a clock that the photons carried along with them; that is the concept that has no meaning.
For example, there are particles from cosmic rays that should not be able to make it to the surface without decaying. However, they're detected all the time. Two valid ways to think of this are:
1. From the Earth's frame of reference time moves more slowly for the particle. This slows down the process of decaying.
2. From the particle's frame of reference the Earth's atmosphere is considerably shorter so it doesn't need to travel as far.
Things get a bit hairy to talk about once you actually reach the speed of light. One way to think of it might be from the photon's frame of reference its entire path has become infinitely short so it had no distance to travel at all.
From the photons frame of reference, then, they do not move at all?
And the environment that photon "experiences", being the path in the universe that it traverses from our point of view; is the past, present, and future (from our point of view) all in instant simultaneity for the photon?
Saying "neutrino has a very small mass" is roughly equivalent to saying "neutrinos very rarely experience an oscillation event (changing into a different flavor)". The distance between the rare events is the "time" it experiences. These are so far apart in spacetime for the neutrino it's experience of time (the way it evolves over spacetime) is extremely slow. More massive particles are "more massive" because they frequently interact with the Higgs field. More interaction events means their experience of time happens faster.
The photon (and anything else with 0 mass) only experiences two events: it's creation and destruction. It moves at c because it's never being slowed down by experiencing interactions.
For a very good explanation of this (with helpful animations) this[1] short playlist (6 ep) of PBS Spacetime episodes.
[1] https://www.youtube.com/playlist?list=PLsPUh22kYmNCLrXgf8e6n...
edit: TL;DR - When speed-of-light particles pause to interact with things (thus moving < c)slowing it down), we say that particle "has mass". Mass is a measure of how frequently those interactions occur (aka how much "time" it experiences).
This is not correct. The worldline of a photon contains events between its creation and its destruction. The spacetime interval between any such pair of events is zero, but that does not mean the events aren't there.
There is no such thing as "the photons frame of reference". It is not even a well-defined concept.
> And the environment that photon "experiences", being the path in the universe that it traverses from our point of view; is the past, present, and future (from our point of view) all in instant simultaneity for the photon?
No, none of this is correct. The reason I keep insisting that all these concepts are not well-defined for a photon is to make it clear why you cannot draw all these inferences that you are trying to draw--they are all wrong. The only way to stop drawing them is to recognize what "not well-defined" means. It means the questions you are trying to ask about photons are meaningless; they are like asking how long the color red is or how much time passes for it. Photons are simply not in the category of things for which those questions make sense.
Even Einstein inserted an anthropomorphized frame of reference into the thought experiments of the celestial objects he contemplated, to explain to others. If we can't ask questions about photons in relation to spacetime as we know it, then what questions can we ask? We certainly don't know spacetime as photons "know" it, since its not "well defined."
Interestingly still, you use the term worldline to describe the totality of the temporal-spatial existence of a photon, so clearly there are concessions to be made and all this is more defined than you assert... and you're lightly reproving us for not using the same dictionary as you...
I'm interested in this subject but not interested enough (or rather, have the time and energy) to become a physicist to understand, if that's what you're going to ultimately suggest to get even a dim, but accurate understanding of the nature of light.
I have done no such thing. I have only closed discussion based on a fallacious premise. If you drop the fallacious premise there is plenty to discuss.
> We certainly don't know spacetime as photons "know" it, since its not "well defined."
I did not say spacetime is not well-defined. Spacetime is not "as photons know it" or as any observer "knows" it. Spacetime is the underlying geometric entity; it requires no "point of view" to exist, or even to be described; you can describe spacetime without ever using inertial frames, which are what your "points of view" actually are.
> you use the term worldline to describe the totality of the temporal-spatial existence of a photon
That's because "worldline" is the standard physics term for it, as used in physics textbooks and peer-reviewed papers.
> you're lightly reproving us for not using the same dictionary as you.
If you want to discuss physics, it helps a lot to use the standard language of physics.
> I'm interested in this subject but not interested enough (or rather, have the time and energy) to become a physicist to understand
You don't have to become a physicist. But you do have to be willing to drop fallacious premises.
Eg distance traveled is 0 due to length contraction. Time taken is 0 due to time dilation. So what's its velocity? 0/0 = undefined, the question is meaningless. But the velocity is arguably more fundamendal than the distance travelled or time taken, so those aren't truly 0. They're also undefined quantities.
No, that is not a correct way to think of it. See my other responses to the poster you responded to.
They can't be. You can't make a conscious subject out of something that has zero mass and moves at the speed of light, and therefore does not have a well-defined concept of "time passing".
> if no time is passing for them, doesn't that mean no space is being traversed either?
It is not the case that no time is passing for a photon. What is the case is that the concept of "time passing for a photon" is not well-defined. That concept not being well-defined means that "space being traversed for a photon" is not well-defined either. That does not mean "no space is being traversed". It means the concept of "space being traversed for a photon" is not well-defined.
This is not correct since "clocks of photon" is a meaningless concept (at least if photons have zero mass, which they do according to our best current models).
The issue isn't that you can't attach a clock to a photon in a practical sense. The issue is that even in principle, the concept of "the clock of a photon" is not well-defined. For it to be well-defined, there would need to be an inertial frame in which a photon was at rest. But that is impossible.
This is not correct, because there is no "reference frame" for a photon moving at the speed of light. The concept of "reference frame" is not well-defined for such objects.
Cool! I learned something new today!
Ultracold neutrons behave very much like ping-pong balls and cannot jump very high
Most of the time. My understanding is that they can tunnel potential barriers, but this isn't that likely to happen in these traps, so it shouldn't affect the results.
(As I understand, they're a little bit magnetic because their constituent quarks are charged.)
More than a little bit. The neutron's magnetic moment is about 2/3 the magnitude of the proton's, and of opposite sign.
No, but it does affect which spin states of nuclei have the lowest energy. For example, the ground state (lowest energy state) of a deuterium nucleus has spin 1--spin of the proton and neutron are parallel--because the opposite signs of the proton and neutron magnetic moments make that state have a lower energy (more tightly bound).
Isn't this always the case, though? I mean, two objects not moving relative to each other is a very specific state and not something that can be held in practice without a negative feedback loop on their relative velocities.
Also spin
https://lansce.lanl.gov/facilities/ultracold-neutrons/experi...
Suddenly you are "on the way to pinning this down." Instead of "Flailing madly in the dark with wild theories."
Like a "stable" civilization?
Sometimes I wonder if clouds of autonomous self replicators, such as our planet and our civilization, aren't viewed as atavistic exponential pests by godlike alien beings who control the entire resources of a civilization in one entity.