EXCERPTS: . . . Pions are kind of like low-mass protons. They also are unstable, decaying in 28 × 10-9 seconds. This lifetime has been measured to incredible precision. If you had a pion and hypothetically accelerated it to the speed of light, which is roughly 300,000 km/sec (186,000 mi/sec), it should travel just over 8 meters (27 feet) before it decayed. But that’s in a Universe in which all clocks tick equally — that is, a stationary human clock and a moving “pion clock” tick at the same rate. They don’t, though.
When scientists create pions traveling at 99.99% the speed of light, they find that they travel about 600 meters (1920 ft) before decaying. That can only happen if fast-moving pions experience time more slowly than stationary ones. By the way, 99.99% the speed of light is not the record for particle accelerators...
[...] Given the effectiveness of Einstein’s equations and the fact that the only limit to the speed of an electron is the speed of light, we can see that the closer we accelerate a clock to the speed of light, the slower it ticks. If it could achieve the speed of light, the clock would stop.
[...] So, what does that mean? From a photon’s perspective, it can pass through the entire Universe without experiencing time at all. Billions and billions of light-years can fly by, in far less than the blink of an eye.
There’s more. While the subject of this article is the passage of time experienced by a photon of light, the theory of relativity also tells us how space is experienced. As objects go faster, the Universe shrinks in the direction they are traveling. Using the same techniques described here, we can also see that for a photon, the Universe is shrunk to zero size. Billions of light-years disappear, meaning that, from the photon’s point of view, it simultaneously exists everywhere along its path of travel... (MORE - missing details)
Shameless clickbait. The author is well aware nothing actually 'breaks down' or 'fails to make sense'.
Only naive misapplication of equations applicable to massive not massless particles leads to any 'paradox'/'weirdness'.
One suspects BigThink.com is pumping contributors to jazz things up in an effort to increase site traffic = $$$ revenue. Sigh.
(Mar 21, 2023 06:08 PM)Magical Realist Wrote: Can a massless particle such as a photon qualify as an inertial frame?
First trying to make sense of the 'tube in the OP..
E=mc^2= m0 /sqrt(1-v^2/c^2)
So he says ( particle energy) /(rest energy) gives time dilation..
(1/m0)*m0 /sqrt(1-v^2/c^2)
= 1/sqrt(1-v^2/c^2)
Looks 'not wrong' but is like trying to explaining genetics by subtracting a llama from a camel.
Why would a 'paid professional' even get involved in this?
Stephen Hawing commented ".. for every equation you include you lose half your readers."..
I may be entirely wrong here .. criticism encouraged.. please!
From the second lne above
E=mc^2= m0 /sqrt(1-v^2/c^2)
or (where m0 is the rest mass and E is the energy)
E= m0 /sqrt(1-v^2/c^2)
If v^2=c^2 we have (1-1)=0 on the bottom line and energy blows up to infinity if m>0.
In a sane universe nothing would travel at 'c' but photons seem to .. (having no mass?)
KorneeMar 22, 2023 03:27 AM (This post was last modified: Mar 22, 2023 03:29 AM by Kornee.)
(Mar 21, 2023 06:08 PM)Magical Realist Wrote: Can a massless particle such as a photon qualify as an inertial frame?
It pays to ask a well-posed question. "Can a massless particle such as a photon qualify as an inertial frame?" is definitely not one.
"Can a photon have a rest frame" IS a well-posed question and the answer is no. Only particles having a finite rest mass can have a rest frame.
(Mar 22, 2023 01:39 AM)confused2 Wrote: Stephen Hawing commented ".. for every equation you include you lose half your readers."..
I may be entirely wrong here .. criticism encouraged.. please!
From the second lne above
E=mc^2= m0 /sqrt(1-v^2/c^2)
or (where m0 is the rest mass and E is the energy)
E= m0 /sqrt(1-v^2/c^2)
If v^2=c^2 we have (1-1)=0 on the bottom line and energy blows up to infinity if m>0.
In a sane universe nothing would travel at 'c' but photons seem to .. (having no mass?)
Towards the bottom of page, under 'Relativistic Energy and Momentum', see eqn (5.10.3) and accompanying text in https://phys.libretexts.org/Courses/Muhl...tic_Energy
It's the generally applicable mass-energy-momentum relation for a particle whether or not it has a rest mass. A photon has no rest mass but of course it does possess a (frame dependent) energy and momentum.
Nice one Kornee. I like the Libretext. Thanks.
I'm still antiphoton - nasty quantum mechanical things pretending to be 'nice' - I'll maybe start a thread when I've got sufficient evidence against them.
(Mar 22, 2023 11:34 AM)confused2 Wrote: Nice one Kornee. I like the Libretext. Thanks.
I'm still antiphoton - nasty quantum mechanical things pretending to be 'nice' - I'll maybe start a thread when I've got sufficient evidence against them.
Glad it was helpful. And now to seemingly contradict my first line in #2. There is imo a yawning 'puzzle' - but it has nothing to do with what the article covers.
Whether one treats EM radiation classically or quantum mechanically as a swarm of photons, a 'consistent' result is that energy content alone contributes to momentum.
According to both SR and GR a numerically equal net contribution should additionally come from the field stresses. The lower three diagonal terms in the so-called stress-energy tensor.
Yet somehow doesn't. Experimentally |p| = E/c certainly works for a photon, and equivalently in terms of power density for classical radiation pressure.
Never seen that even raised elsewhere as an issue let alone explained. Weird. Might be missing something obvious but can't see where.
[Stress contributions are addressed for say a moving capacitor 'paradox' e.g. see: https://phys.libretexts.org/Bookshelves/...etic_field
but are moot there - equilibrium constraints zero out total field + mechanical stress contributions.]
To elaborate on the above becomes too involved and sidetracks substantially from the OP, so will leave it at that.
EXCERPTS: . . . [...] Given the effectiveness of Einstein’s equations and the fact that the only limit to the speed of an electron is the speed of light, we can see that the closer we accelerate a clock to the speed of light, the slower it ticks. If it could achieve the speed of light, the clock would stop.
[...] So, what does that mean? From a photon’s perspective, it can pass through the entire Universe without experiencing time at all. Billions and billions of light-years can fly by, in far less than the blink of an eye.
I assume that would also apply to a spaceship that could attain a large percentage of the speed of light.
Quote:There’s more. While the subject of this article is the passage of time experienced by a photon of light, the theory of relativity also tells us how space is experienced. As objects go faster, the Universe shrinks in the direction they are traveling. Using the same techniques described here, we can also see that for a photon, the Universe is shrunk to zero size. Billions of light-years disappear, meaning that, from the photon’s point of view, it simultaneously exists everywhere along its path of travel...
At light speed, Einstein’s equations break down and nothing makes sense
Yes, I agree with that. The speed of light in Einstein's Special Relativity appears to me to be a singularity in the mathematical sense. Physical quantities like measures of time and space behave asymptotically as they approach closer and closer to the speed of light as a mathematical limit.
KorneeMar 23, 2023 01:00 AM (This post was last modified: Mar 23, 2023 01:58 AM by Kornee.)
Quote:
"So, what does that mean? From a photon’s perspective, it can pass through the entire Universe without experiencing time at all. Billions and billions of light-years can fly by, in far less than the blink of an eye."
To anyone properly versed in SR, the notion of 'from a photon's perspective' is a nonsensical proposition. As one hypothetically 'catches up' to a photon, it redshifts out of existence. Poof. Gone. Ergo - there is no sense in imagining what a photon 'sees' or 'experiences' in it's own nonexistent 'rest frame'.
Even for an ultra-relativistic non-zero rest mass particle such as an electron, the notion it 'sees' the rest of the universe contracted to a thin pancake is wrong.
No point going into details but suffice to say all it really 'sees' is it's locally accessible environment relativistically contracted and Doppler blueshifted/redshifted in an angular dependent manner. That's it.
Well not quite. There are other matters like partial orthogonal transformations of static E and B fields into each other. And the visuals are not just that of contraction in the direction of motion, curvilinear distortions too.
One YouTube presentation: https://www.youtube.com/watch?v=5XmJrQdsqyQ
Mar 20, 2023 04:13 AM
(This post was last modified: Mar 20, 2023 04:13 AM by C C.)
