where does light from a torch go?

"...in which a person exits Door #2 of a room to find he just entered Door #1 of the same room."

Have you ever played "portal"? Brilliant game.
 
I don't think photons exist until they hit something.

Why don't photons collide with each other. There must be trillions of them passing at any chosen minute coordinate.
 
exchemist said:
But this is as pointless an argument as that of Bishop Berkeley. If the photon behaves as if it exists whenever it is measured, then to speculate as to whether it may cease to do so in between is utterly moot.

To put it another way, if, to borrow a legal phrase, it exists at all material times, then that's what we mean when say it exists.

This can be seen as the Occam's Razor principle, yet again. Since all observations can be explained by postulating continuity of its existence, addition of a further postulate, that perhaps it ceases to exist when not observed, adds nothing. It is against science to add unnecessary postulates.
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It's solipsist nonsense. Stuff doesn't exist until it bumps into something else that doesn't exist until it's observed by dav75.
 
Nothing stays the same. Everything has to have somewhere to go. I think every journey is a path already laid.
 
dav57 said:
I don't think photons exist until they hit something.

Why don't photons collide with each other. There must be trillions of them passing at any chosen minute coordinate.
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Have you ever seen a wave collide with another wave? No, they pass through each other, don't they?

Why not try learning a bit of science, eh? People have been thinking about all this stuff, you know.
 
exchemist said:
Have you ever seen a wave collide with another wave? No, they pass through each other, don't they?

Why not try learning a bit of science, eh? People have been thinking about all this stuff, you know.
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Light is a wave, until it hits something, then it collapses into a photon, but only when it hits something. Is that right?
 
...so the act of observing something (or at least something receiving energy/information) changes the form such that wave becomes particle. Observation creates change. Yes or no?
 
dav57 said:
...so the act of observing something (or at least something receiving energy/information) changes the form such that wave becomes particle. Observation creates change. Yes or no?
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What I mean is that photons have wave properties. They are not billiard balls.

It appears you may have half taken in some simplified version of the principle of indeterminacy and now seek to play silly games with it. I'm not embarking on a tutorial with you. It would be a waste of time.
 
Does observation create change? Yes or no?
Does light change from a waveform to a particle when observed? Yes or no?
 
dav57 said:
Light is a wave, until it hits something, then it collapses into a photon, but only when it hits something. Is that right?
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No it's wrong. Light consists of photons. No photons no light. But photons are wave-like as well as having some particle-like behaviour. http://en.wikipedia.org/wiki/Photon

If you don't already know this, you should stop demanding one word answers to selected questions that you think support your silly ideas and just learn some science first.
 
dav57 said:
I don't think photons exist until they hit something.
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Being wrong is a right, but I don't see why you would want to. This position of yours just doesn't make logical sense. You know *something* was emitted because you can measure the emission and energy loss. So what do you think happens when a flashlight battery discharges and you aren't watching the light?
Why don't photons collide with each other. There must be trillions of them passing at any chosen minute coordinate.
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Same reason no other waves collide with each other: they have no volume.
 
"Light consists of photons."

But when they're travelling, they're waves. That's why they don't crash into each other. Do you agree with that or not?

So it's only when they hit something that can absorb them that they convert to photons. The particle-like behaviour only comes out once observed. Yes?
 
dav57 said:
"Light consists of photons."

But when they're travelling, they're waves. That's why they don't crash into each other. Do you agree with that or not?
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A photon is a photon is a photon. Always.
So it's only when they hit something that can absorb them that they convert to photons. The particle-like behaviour only comes out once observed. Yes?
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The behavior of light depends on how you choose to observe it, but that doesn't change that it is always still light. What you are saying is like saying water is only H2O when it is liquid, but not when it is solid -- nonsensical. And you are getting off track here because this has nothing to do with observing the emission and absorption. Please answer my question:
You know *something* was emitted because you can measure the emission and energy loss. So what do you think happens when a flashlight battery discharges and you aren't watching the light?
 
dav57 said:
"Light consists of photons."

But when they're travelling, they're waves. That's why they don't crash into each other. Do you agree with that or not?

So it's only when they hit something that can absorb them that they convert to photons. The particle-like behaviour only comes out once observed. Yes?
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No! Re-read my post, that of RW and the link I gave you. Photons are photons and have both wavelike and particle-like attributes, depending on the circumstances.

It is true that one of their particle-like attributes is that they are absorbed in whole units of energy. However, these whole units are multiples of hν, where h is Planck's constant and ν is the frequency of their wave. So they are both, or neither. The whole discipline of Quantum Mechanics has been developed to deal with this observed wave-particle duality at the atomic scale. So please don't try to reduce it to a couple of Fox News soundbites.
 
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"You know *something* was emitted because you can measure the emission and energy loss. So what do you think happens when a flashlight battery discharges and you aren't watching the light?"

I agree, it goes somewhere, but only if there is something to connect to which can receive the energy transfer. if the light can't physically transfer energy to something else, I'm querying whether it would actually leave the source in the first place.
 
"Photons are photons and have both wavelike and particle-like attributes, depending on the circumstances."

I agree. All I'm asking is whether the wave-like attributes are only ever evident in flight? And is the particle component only every evident following absorption?

From what i can see of the double-slit experiment, its results support what I am suggesting. Multiple waves in flight interfere and then convert to distributed particles at the screen where they are received (or observed).

Even where a single photon is emitted, one after the other, each photon remains as an energy wave during flight and takes all available paths as the wave is spit. When it reaches the observation screen, it collapses into a particle (but only as a result of being observed). The pattern is still evident because the light was always an interference-potential wave right up until observation.

It appears to me that this is why trying to observe the photon at one of the slits effectively breaks the wave down into a particle and destroys the potential for interference at the screen.
 
dav57 said:
"You know *something* was emitted because you can measure the emission and energy loss. So what do you think happens when a flashlight battery discharges and you aren't watching the light?"

I agree, it goes somewhere, but only if there is something to connect to which can receive the energy transfer. if the light can't physically transfer energy to something else, I'm querying whether it would actually leave the source in the first place.
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Why don't you do an experiment: point a strong laser into space and see if there is any difference in its power draw if you put your hand in front of it or move it away. You will find that there is not.

This is settled science that is easy to verify. No need for "what ifs".
 
dav57 said:
if the light can't physically transfer energy to something else, I'm querying whether it would actually leave the source in the first place.
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Yes. If I shine my torch at the moon it will take approximately 1 second to reach the moon. When the photons hit the moon they would be absorbed. So the answer is yes they existed that whole second. If I did not shine the torch at the moon and instead pointed it at mars it would take several minutes for the photons to travel that distance. The photons that hit mars would be absorbed and the ones that missed would not be absorbed. Both sets of photons would exist for the entire several minutes, the one that were not absorbed would continue to exist and move through space until the were absorbed (or travel forever if not absorbed).
 
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