Flashlight at the speed of light

If you accelerated a flashlight at the speed of light, what would happen?

A. The light from the flashlight would be emitted as twice the speed of light.

B. The flashlight would not emit any light at all.

C. The light beam would trail the flashlight.

D. None of the above.

Why?

 

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Nothing with mass can be accelerated to light speed.

 

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Light always travels at the speed of light.

 

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As already stated, your flashlight cannot be accelerated to the speed of light, It can be accelerated to any speed shot of the speed of light just not to the speed of light. ( And please do not respond with "But what if we could accelerate it up to light speed", because there is no answer to that question. If you make that assumption, you are also assuming that laws of the universe are not what we understand them to be, in which case we are left with nothing to derive an answer from.)

So, let's instead deal with something we can answer, a flashlight traveling at almost the speed of light, say 0.99999999 c with respect to some observer. For that observer the light would travel at c with respect to himself and at 0.00000001 c relative to the flashlight. After one second of the light being turned on, the front of the beam will be ~3 meters from the flashlight.

On the other hand, if you are the person holding the flashlight, the light travels at c with respect to you, and after one second the front of the beam will be ~300,000 km away from the flashlight.
As far as you are concerned, things behave just as if you are standing still and it is the other observer that is flying past you at 0.99999999c.

 

Let's up the anne on this question.

Paired entangled electrons within the same energy shell of an atom may flip spins and sometimes emit a photon as a result. These are known as hyper fine energy transitions and we know for certain they happen because we can observe such transitions with a spectrograph.

Let one of these transitions be your relativistic velocity flashlight. There isn't any question that the transition can occur because entanglement happens faster than energy propagates, or in other words, outside of the realm of the equations which describe time dilation effects related to the propagation of energy or matter.

Forget the beam of light from the flashlight. Can the entangled electrons change state or not? If they do, there is physics we must understand related to time that is beyond the bounds imposed by relativity. And it is evident that such transitions can occur.

This does not violate the single assumption on which relativity is based. But it suggests rather strongly that c is not a limit on any process which is not really dependent on the propagation of energy.

 

Good question Dan! But this is beyond my paygrade. Anyone?

 

My limited understanding would have me simply answer that as yet the quantum realm and quantum weirdness that we see and use everyday is not fully understood.
So we don't know, but I'm willing to have that answer surpassed by others more knowledgable in this area of physics.

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This idea seems to come up again and again in threads about time dilation in the vicinity of EHs of black holes, and also infinite time dilation applied to entangled photons already traveling at c. Traveling at c, entangled photons may not have an observer traveling with them, but observers at rest can see them some time delay after they are emitted. If one of an entangled pair of photons is projected forward, and one backward, a change of entanglement state in one is instantly transferred to the other.

I don't have an answer. I'm just a little bored with the relativistic flashlight paradox, so I invented a sort of entanglement flashlight not bound by the usual relativistic energy or matter propagation trappings. Feel free to elaborate on the experiment if anyone has any ideas about testing the idea, or ignore it if you don't. The flashlight paradox is perfectly fine science all by itself.

 

There was an experiment done at the LHC with decaying muons. Muons accelerated close to c decayed into photons and that did not exceed c.

 

Muons are of course quark-antiquark pairs or quads. The component quarks possess fractional electric charge, color charge, and mass.

Neither energy nor matter can exceed c as a limit to propagation speed in a vacuum. But this does not suggest that changes in entanglement states may not "travel" faster, although it is up for grabs as to whether this is actually traveling, or are simply the result of an interactions with a pervasive quantum field that is defined to be the one that is at rest with respect to virtual particle (energy) pair creation, etc. Entangled photons traveling in exact opposite directions are never truly separated. Any apparent distance in the exact opposing directions of propagation is Lorentz contracted to identically zero.

 

How long can an electromagnetic wave travel in a vacuum before it calapses into a photon, I bet you will say forever...

 

Having earlier acknowledged that 'being in the rest frame of a photon' is impossible, you here resurrect it as though viable. Strange, but not untypical. 'In the rest frame of a photon' nothing happens yet everything happens at once - the photon lifetime is precisely zero, as is the longitudinal extent and lifetime of the universe, as is the energy of said photon (hence it doesn't 'really' exist). Such absurdities is why folks who know better never appeal to the concept of 'being in the rest frame of a photon'.

 

The universe still has 'extent', just not in the exact direction of propagation, or the exact direction from which the photon was sourced, or its entangled twin.

This makes perfect sense in a universe in which there is only time, energy, and one more degree of freedom that is related to the direction of energy propagation. From these elements and the inertialess quantum fields underlying them, you derive matter (bound energy frozen in time like this flashlight example) and space, which is the same as energy traveling at c in every direction, from every point along each direction it may propagate. Space is the illusion. That, along with the illusion that energy propagation is a hard lower limit on the graininess of time for beings who are composed of matter plus energy like ourselves. Entanglement proves this is not the case.

 

Firstly, a correction. I wrote "..folks who know better never appeal to the concept of 'being in the rest frame of a photon'." In hindsight, that's not quite accurate. Roger Penrose in a way appeals to just that as a loose argument in favor of his CCC aeons idea. Which idea I do not dismiss lightly. Currently there are huge issues with any of the 'mainstream' competing cosmological theories. Eternal inflation is essentially dead but it's die-hard proponents won't concede - yet anyway. In another thread I pointed to entropy as the killer of oscillating 'monoverse' theories, something known way back, and remains a roadblock despite clever attempts to skirt it. Ekpyrotic is a variant with better hopes but it has it's own conceptual difficulties.

As for your other notions above, good luck with getting traction from those accustomed to rigorous conceptual and mathematical approaches.

 

I have a stupid question. You can't push a flashlight up to light speed anyway. But could you 'knock' a photon with another photon somehow to push it up to beyond lightspeed? If so, what happens?

 

Photons having zero rest mass basically by definition always travel at c in every frame. Moreover being massless Bosons they interact with each other almost never. That gives enough clues?

 

You cannot make a photon or anything else composed of matter and/or energy propagate faster than c in a vacuum.

 

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Oh, COME ON, boffins! Let's make this work!​

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The said boffins.​

 

Those are some great boffins you have there! Vanuatu does resemble a paradise.

You may make the flashlight get as arbitrarily close to light speed as you wish (or simply wait long enough for the expanding universe to accelerate it to that speed relative to something at the opposite end of the universe). But 0.999999…. times the speed of light, is not actually the speed of light is it? Or isn't it?

Matter is energy. Collide your flashlight with an antimatter flashlight. The photons produced will not be able to go any faster. Unless the boffins know a better way?

 

Well first off you can't reach the speed of light. But let's say you get so close that for all intents and purposes you are at the speed of light. What you see depends on where you are.

If you are in front of the flashlight, at rest with respect to the rest of the universe, you would see a hard-UV light source coming straight at you. The photons would be incredibly energetic (i.e. would fry you almost instantly) and of course would be followed an almost-immeasurable time later by the flashlight itself, so you best get out of the way very quickly, especially since the flashlight, if it hit you, would pack more energy than a nuclear bomb. The photons would not be going faster than the speed of light, but the energy that the moving flashlight imparted to them would be measurable by their increased frequency (and thus increased energy.)

If you see the flashlight zoom by from the side, you wouldn't see the light of course (nothing to reflect it in space) and the flashlight itself would look considerably shorter due to length contraction. It would be hard to see since it would be in front of you for picoseconds.

If you were flying along next to the flashlight, it would appear normal size and the light coming out the front would appear normal, and would be traveling at the speed of light.