That's nonsense.beatrix kiddo said:hahahaha.. there we go. now let's really get the ball rolling and just come and say that anyone who says the photon is destroyed contradicts einstein! i don't agree with sir Albert (on many levels), but tom does. so make a choice. either the photon gets destroyed or the velocity of light changes.
Matter and energy can't be created or destroyed, only converted from one to the other. Photons aren't matter and they aren't energy (though they carry energy). Think of it this way: a sound wave is created at your speaker and destroyed when it is absorbed by your eardrum. The energy is conserved.urtalkinstupid said:I thought there was a law that said nothing can be created or destroyed. Energy and matter wise. Is that true?
I don't believe, I know. There is a big differnece. Light does not stop, photons are destroyed, and energy is conserved. This has been explained now about half a dozen times.the velocity of light changes because the photon (the light) is stopped. or do u believe the photon gets destroyed? and if u believe the photon gets destroyed, but u don't think the energy gets destroyed...
Maybe this is the problem. See my sound wave analogy above....a photon is energy...
The photon keeps going full throttle till all of a sudden there is no more photon. Instead there is a more energetic electron. There is no time lag between the transition in which you could say there is a photon with no velocity, a "stopped" photon.beatrix kiddo said:the velocity of light changes because the photon (the light) is stopped.
urtalkinstupid said:I just thought of something. Take an object and accelerate it to .8c and then let it go about a constant velocity. Right when that object reaches .8c and light beam next to it wille mitt. How fast will that light beam be going with respect to the object. If the speed of light does not change, would it be c? I don't think it would c. I don't know though. Maybe there is a way around this paradox.
Outstanding.Chronos said:Pitcher throws photon to mirror. Mirror hands photon to umpire. Umpire discards it and and hands new photon to mirror. Mirror tosses new photon back to pitcher.
Yes. Its called Special Relativity. It states that the speed of light is constant for all observers regardless of their inertial frame of reference and that the laws of the universe are the same everywhere.urtalkinstupid said:I just thought of something. Take an object and accelerate it to .8c and then let it go about a constant velocity. Right when that object reaches .8c and light beam next to it wille mitt. How fast will that light beam be going with respect to the object. If the speed of light does not change, would it be c? I don't think it would c. I don't know though. Maybe there is a way around this paradox. [emphasis added]
Right.BobG said:Light hitting a highly reflective surface causes a small change in the satellite's momentum.
Right.Light hitting an absorbant surface causes an even smaller momentum change in the satellite
Says who?(a totally absorbant surface would impart no momentum change to the satellite).
It's no different than bouncing a ball against a wall. The ball has incoming momentum +p. If it bounces back (like a superball), then it's final momentum will be -p, so \Delta p = -2p. If it's absorbed (like a putty ball), then the final momentum is 0 (assume a massive wall) and \Delta p = -p. The ball that bounces off transfers more momentum to the wall that the one that sticks.It would seem to me that, in the interests of energy conservation, absorbant materials would change the momentum more than reflective materials.
Any comments on why the actual behavior is so counter-intuitive?
Doc Al said:Right.
Right.
Says who?
It's no different than bouncing a ball against a wall. The ball has incoming momentum +p. If it bounces back (like a superball), then it's final momentum will be -p, so \Delta p = -2p. If it's absorbed (like a putty ball), then the final momentum is 0 (assume a massive wall) and \Delta p = -p. The ball that bounces off transfers more momentum to the wall that the one that sticks.
BobG said:Solar Radiation Pressure. For high altitude satellites, the overall perturbations are so small that the solar radiation pressure begins to become a significant factor affecting satellite orbits.
Light hitting a highly reflective surface exerts a force on the satellite. Light hitting an absorbant surface exerts an even smaller force on the satellite.
I've taken this as a given without worrying to much about the details, but this discussion kind of piques my curiosity about why this happens.
It would seem to me that, in the interests of energy conservation, absorbant materials would change the momentum more than reflective materials.
Any comments on why the actual behavior is so counter-intuitive?
Oops! Edited to remove inaccurate statement - totally absorbant materials still receive some force from light energy, just less.
Actual equation is:
F=\frac{F_sA}{cm}(1+q)cosi
where F_s is solar pressure or 1367 \frac{W}{m^2}
c is speed of light
m is mass of satellite
q is reflectivity (1 for totally reflective, 0 for totally absorbant)
i is incidence angle
On an asymetrical satellite design, similar to the NOAA GOES weather satellite, the torque from solar pressure would be in the range of 5.54 x 10^-4 Newton meters. Small, but still the largest factor affecting satellite attitude.
beatrix kiddo said:i still disagree. i mean a photon is energy right?
well if the energy isn't destroyed then the photon isn't destroyed.
maybe stewarta is correct. maybe the photon gets stopped by the mirror and then the photon is accelerated at c, back off the mirror.
BobG said:Makes sense as long as I stay on the surface. The photons being absorbed by atoms and then released adds some confusion factor.
But, when I think about it, it could be thought of as the photon's kinetic energy has been converted to potential energy when the electron level is raised. When the electron falls back into its original orbit, the potential is reconverted back to kinetic energy.
BobG said:I take back the comment about thinking it made some sense.
If the satellite were massive and did not move, it would make sense. The light leaves with the same amount of energy it left with. The fact that the satellite does move due to solar pressure means some of the energy has been transferred to the satellite.
I'm having trouble figuring out how everything balances out.
Of course, the energy of light depends not upon its speed, which is constant, but upon its intensity and frequency. So, if the satellite moves away from the light source, the light reflected must be emitted at a lower frequency than it had when it first struck the surface.
Close?
Take a speed and reverse it, you get -v. Since the energy equation includes v^2, the minus signs cancel out and you get the exact same energy as you had before, but in the opposite direction.BobG said:If the satellite were massive and did not move, it would make sense. The light leaves with the same amount of energy it left with. The fact that the satellite does move due to solar pressure means some of the energy has been transferred to the satellite.
I'm having trouble figuring out how everything balances out.
Doc Al said:It's no different than bouncing a ball against a wall. The ball has incoming momentum +p. If it bounces back (like a superball), then it's final momentum will be -p, so \Delta p = -2p. If it's absorbed (like a putty ball), then the final momentum is 0 (assume a massive wall) and \Delta p = -p. The ball that bounces off transfers more momentum to the wall that the one that sticks.
Chronos said:The used to sell light pinwheels in novelty shops [still do, i suppose]. The 'clockwise' face of each vane is painted white, the opposing face is painted black. It is suspended in an evacuated glass container to eliminate air resistance. When exposed to bright light, the wheel spins clockwise.
russ_watters said:Take a speed and reverse it, you get -v. Since the energy equation includes v^2, the minus signs cancel out and you get the exact same energy as you had before, but in the opposite direction.
Momentum, on the other hand, has just v...
That's a Crookes' Radiometer. It doesn't rotate because of the light hitting the vanes, though. It is chronically sold with that misinformation in accompanying literature. This site explains how it actually works:Chronos said:The used to sell light pinwheels in novelty shops [still do, i suppose]. The 'clockwise' face of each vane is painted white, the opposing face is painted black. It is suspended in an evacuated glass container to eliminate air resistance. When exposed to bright light, the wheel spins clockwise.
Right! If light pressure were the cause of the vanes spinning, the vanes would spin in the opposite direction than they do.zoobyshoe said:That's a Crookes' Radiometer. It doesn't rotate because of the light hitting the vanes, though. It is chronically sold with that misinformation in accompanying literature.
Well sure - but who said anythign about reducing v? All you are changing is the sign. The magnitude stays the same.BobG said:If you reduce v, don't you also reduce v^2?
russ_watters said:Well sure - but who said anythign about reducing v? All you are changing is the sign. The magnitude stays the same.
omin said:Two gods have bats made made of pure mirrorium. The pitcher throws photons at constant c, but each gods swings their bats at different speeds.
The photon enters the mirror with a speed based upon the perspective of it's last source, but this same photon does not leave the mirror it entered. You're all saying another photon leaves. This photon is manifested in the new reflection source and leaves at a rate based upon where it manifested. It follows Newtons laws launching forth from it's new source, forgeting it's previous launch conditions.
It sounds correct to say light's speed is constant, but it's constant from a source which means lights speed is determined by a combination of the source where it's manifested and the properties of light itself.
If a light is reflected, the source where reflection occurs can increase the lights velocity to a orginating source faster than light left the source originally, just by the newly reflecting source simply accelerating during the reflection process in the direction toward the previous source.
Correct or incorrect?
BobG said:The bat receives photons at a certain rate. It emits the photons at the same rate it received them. But, since the bat is moving, the photons are emitted closer together. That means another observer receiving the photons from the bat will receive them at a higher rate than the bat actually emitted them.
BobG said:Since the late swinging god's bat is moving faster, they could only hit one photon each at the exact same time. Both would receive the photon at the speed of light - both would send the photon skyward at the same rate.
Omin said:Does each photon emerge from the bat at the same speed, relative to the playing field?
Omin said:Do the photons absorb into each bat at the same rate? Does the new photon manifestation process occur at the same rate in each bat?
If photon absorbtion and manifestation is simultaneous, and emergece of photons from the bat have the same speed, where does the extra energy go that the late swing god exerted in his swing?
Speed c is determined by the source or what?
If the photon is unaffected by the instataneous intertia of the bat during it's emergence from the bat, then its speed c of emergence is relative to what?
If the photon is affected by the instantaneous inertia of the bat (it's physical origin now), then it should move speed c from the instantaneous inertia of the bat, right?
terrabyte said:if it's just one photon, energy of the swing makes no difference.
photons have no mass to be accelerated in this fashion
Newton's laws have well known limitations and that's one of them.omin said:If photons don't have mass, then should I throw out Newtons Laws? Newtons laws seem to me to imply mass to anything sensed. Or what?
Since when? That's an assumption based on a narrow-minded view.Only things with physical properties can be sensed, which is only directly by humans or human aided sense, instruments. All things with physical properties have the property of mass. (Empiricism, Technology, The Physical Property of Mass and NL III)
russ_watters said:Newton's laws have well known limitations and that's one of them. Since when? That's an assumption based on a narrow-minded view.
All waves, by definition, have no mass.
omin, you asked a lot of questions about C in previous posts. Have you read what Special Relativity has to say about it? It's the second postulate you should be concerned with.
omin said:Waves are psychologial theories, which are physically subjective as we speak.
The book Wu Li Masters claims physically objective originating cause of the subjective wave theory through descriptions of past experiments.
russ_watters said:All waves, by definition, have no mass.
You mean like sound (or maybe I don't know what a "matter wave" is...)? Sound waves ride on air, which has mass - sound waves themselves do not.Tom Mattson said:Matter waves have mass.
A matter wave is more of a verb than a noun. It is not a thing but rather something which describes a thing. The term matter wave usually refers to the wavelike characteristics of the probability distribution associated with a particle which has a non-zero proper mass. I spose that it can apply to a photon to since all the wavelike properties of a photon are identical to the wavelike properties of any other particle and as such they don't depend ont he particle's proper mass.Tom Mattson said:Matter waves have mass.
For simplicity consider a single isolated atom in an inertial frame of reference. In this frame the atom emits a photon. The atom recoils because the photons are emited. This can be described by saying that in order for the total momentum of the system to be conserved the atom must have momentum and that means it must move. The amount of energy the photon has is directly related to the final speed of the atom. The higher the photon energy the higher the final speed of the atom. If the atom is in a body then, for the purposes of analyzing the dynamics, you can simply consider the body to be that which emits the photon.omin said:Interesting. We sense the atom recoil. Do atoms recoil between photons emiting or just when photons emit? If they only emit when the photon leaves, the photon is involved in the recoil.
omin said:Interesting. We sense the atom recoil.
Do atoms recoil between photons emiting or just when photons emit? If they only emit when the photon leaves, the photon is involved in the recoil.
The state of the atoms interia (in respect to another atom in non-uniform motion) does not determine the photons speed, but the photon emission process determines the recoil? This appears to represent a violation of N III Law.
The velocity of the body which the atom resides and the velocity of the atom in the body does not determine the photons speed from the atom?
russ_watters said:You mean like sound (or maybe I don't know what a "matter wave" is...)? Sound waves ride on air, which has mass - sound waves themselves do not.
Chronos said:You lost me there, Tom. Waves, by definition, have no mass, just mass potential.
pmb_phy said:A matter wave is more of a verb than a noun. It is not a thing but rather something which describes a thing. The term matter wave usually refers to the wavelike characteristics of the probability distribution associated with a particle which has a non-zero proper mass.
I spose that it can apply to a photon to since all the wavelike properties of a photon are identical to the wavelike properties of any other particle and
as such they don't depend ont he particle's proper mass.
They recoil as a direct result of emission (or absorption, for that matter) of photons. This is because the photon carries momentum and energy, and both are conserved quantities.
