where does light from a torch go?

dav57 said:
How do you know that photons that don't strike anything exist? Please tell me. I want to know. If you don't know the answer, just say so. You can't just assume something you can't measure exists, can you?
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The answer still hasn't changed from post #8, except that now you made it YOUR premise. We know they exist because you stated they exist as the premise of your question!

If we remove all the repetition, you basically said: 'a photon exists; how do we know it exists'?

Perhaps turning it around might help: when you said the photon is emitted from the light source, how did you know that to be true?
 
dav57 said:
How do you know that photons that don't strike anything exist? Please tell me. I want to know. If you don't know the answer, just say so. You can't just assume something you can't measure exists, can you?
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Of course we can.

We all extrapolate from what we can measure and detect, to predict the behaviour of aspects of the world that we can't detect or measure. This is how we model the physical world. Anyone who thinks the sun is not emitting radiation in all directions, because we can only measure the tiny part of it that is incident on the Earth, needs his head examined. Or, how do you think the theory of plate tectonics works, given that we can't measure the movement of the rocks of the mantle? Or, how do you think the theory of evolution works, given that we cannot (in most cases) observe evolutionary changes between successive generations of living organisms?

We infer, from the measurement we can make, the behaviour of systems that we cannot measure.

I am very surprised to be having this discussion.
 
dav57 said:
How do you know that photons that don't strike anything exist? Please tell me. I want to know. If you don't know the answer, just say so. You can't just assume something you can't measure exists, can you?
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We know the CMBR photons exist and they travel forever whether they bump into something or don't bump into something. They can't be absorbed because the CMBR photon energy is < required for interaction with matter. To interact with the hydrogen atom the minimum is ~ 13.7eV. The existence of the CMBR photons IS 'the kind' for doing cosmological science.
 
The Sun does emit in all directions because the light has somewhere to connect with and transfer energy. A light source at the edge of the universe facing outwards is a different story as the light transfers the energy to nothing.

If the energy has been released from the source, and conservation applies, then the energy must remain in the light wave forever as it travels through nothing. Is that right?
 
"We know the CMBR photons exist and they travel forever whether they bump into something or don't bump into something."

But if they don't bump into anything or interact with anything such that they can't be detected then how do we know that the undetected ones actually exist? Are you sure that the actual observation (or measurement) - or act of receiving the energy - isn't the key to something 'coming into existence'?

The light being emitted from the torch facing outwards towards nothing doesn't really exist, does it? If there is no observer, or no transfer of energy from one entity to another, then you may as well say that the emitted energy doesn't exist. It's not measurable. It's nothing.
 
Yes I'm sure. Because the Sun is in a closed system which has grown over 13 billion years and is entirely connected and capable of transferring energy and information within its boundary.

There was once a time, though, when outward-facing light had nowhere to travel and connect with.
 
If there is no observer, or no transfer of energy from one entity to another, then you may as well say that the emitted energy doesn't exist. It's not measurable. It's nothing.
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It's measurable. It just hasn't been measured. You can't say it doesn't exist because you haven't looked at it.
 
You have to accept that there are some things that cannot be measured, now, or ever. A torch emitting energy at the speed of light outward away from our closed universe is impossible to measure. It doesn't exist.
 
dav57 said:
"We know the CMBR photons exist and they travel forever whether they bump into something or don't bump into something."

But if they don't bump into anything or interact with anything such that they can't be detected then how do we know that the undetected ones actually exist? Are you sure that the actual observation (or measurement) - or act of receiving the energy - isn't the key to something 'coming into existence'?

The light being emitted from the torch facing outwards towards nothing doesn't really exist, does it? If there is no observer, or no transfer of energy from one entity to another, then you may as well say that the emitted energy doesn't exist. It's not measurable. It's nothing.
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That's what the experimental science associated with the CMBR is all about. You can read about the experimental model and the results of the empirical measurements. Really interesting cosmological science.

WMAP

http://map.gsfc.nasa.gov/

They're pretty good at explaining how the experiment works. IE the details associated with the science of the CMBR photons.
 
dav57 said:
You have to accept that there are some things that cannot be measured, now, or ever. A torch emitting energy at the speed of light outward away from our closed universe is impossible to measure. It doesn't exist.
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Nonsense. You're saying that if you don't see something, it doesn't exist.
 
dav57 said:
You have to accept that there are some things that cannot be measured, now, or ever. A torch emitting energy at the speed of light outward away from our closed universe is impossible to measure. It doesn't exist.
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What's extraordinary about your thinking? Looks to me like 'what's extraordinary' is a lack of accomplishment due to lack of effort. Light emitted from the torch does exist regardless what you think. So it's not impossible to measure as you suggest. Really, you think the torch is different from your flashlight? I don't get it? Ever hear of commonsense? Good scientific tool when it's exercised in the intellectual honest way.
 
dav57 said:
You have to accept that there are some things that cannot be measured, now, or ever. A torch emitting energy at the speed of light outward away from our closed universe is impossible to measure. It doesn't exist.
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There are two misconceptions here.

One is that the universe has a boundary, which you can get light to exit through. This is false. There is no edge to the universe, and you cannot get any energy or matter to exit the universe to somewhere else.

The second is your barmy idea that photons don't exist until they are absorbed. This seems to be Bishop Berkeley all over again: http://en.wikipedia.org/wiki/George_Berkeley

I repeat, you cannot make any model of the physical word without extrapolating, from the limited set of measurements we can make, to how matter and energy behave when they are not under observation.

That is just science. If you want to indulge in arid metaphysical speculations I can't stop you, but please don't attempt to convince anyone else on this forum. As far as building a predictive model of reality, which is what science is concerned with, this sort of thing is an utter waste of time.
 
How do we know that a photon doesn't only appear as a photon, so to speak, before it interacts with an observer (or any other form of receiver of the energy/information)?

How do we know that?

"Nonsense. You're saying that if you don't see something, it doesn't exist."

Not exactly. But if you are affected in no way, shape or form by an event, either directly or indirectly, then yes, it doesn't exist until you can measure it and draw data/information from it. Even if it does exist, it may as well not exist, at least until it affects you.
 
dav57 said:
How do we know that a photon doesn't only appear as a photon, so to speak, before it interacts with an observer (or any other form of receiver of the energy/information)?
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Because the energy emission can be measured and has to have an explanation. If you turn on a flashlight, verify it is working, then point it away from you, you'd need a reason to believe the light stopped working, not a reason to believe it kept working.
Not exactly. But if you are affected in no way, shape or form by an event, either directly or indirectly, then yes, it doesn't exist until you can measure it and draw data/information from it. Even if it does exist, it may as well not exist, at least until it affects you.
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That's pseudophilosophical nonsense. If a tree falls in the woods and no one is there to hear it, it still makes a sound. How do we know? Consistency. The laws of the universe don't exist for our viewing pleasure. They don't turn on and off when we are around or leave.
 
If (theoretically)you stand on the inside of a black hole and face a flashlight outwards, does the light energy exit and travel anywhere and does the energy source (battery) deplete?
 
dav57 said:
If (theoretically)you stand on the inside of a black hole and face a flashlight outwards, does the light energy exit and travel anywhere and does the energy source (battery) deplete?
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The energy does not leave the black hole and the battery depletes.
 
This sounds like a very smart energy efficient flashlight to me, It won't emit photons if it knows there's nothing to illuminate.
 
nimbus said:
This sounds like a very smart energy efficient flashlight to me, It won't emit photons if it knows there's nothing to illuminate.
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Interesting. I can't think of how it could do that without using photons. :D
 
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