Although this sounds like science fiction, such a delayed choice experiment using terrestrial photons proposed in 1978 by John Archibald Wheeler, then at Princeton University. The experiment was carried out in college Park, Maryland in 1985 by Carroll Alley, Jakubowicz, and William Wickes of the University of Maryland. The Alley, Jakubowicz, and Wicks experiment was done with mirrors. A pulse of light is fired at a half-silvered mirror. Half of the light passes through the splitter and half is reflected at right angles to the direction of the incident pulse. By electronically inserting a switch strategic location in the setup, they were able to manipulate the light just before it was observed. If the switch was on the light was directed into a photodetector, confirming the particle like properties of light and that the photon of light went along one path. If the switch was off, the two split beams of light were combined and the two waves were made to interfere with each other. The interference pattern confirmed that the light wave went along both paths.
The light behaved like a particle when particlelike properties were measured and it behaved like a wave when wavelike properties were measured. The remarkable novelty of the result is that the experiment was arranged so that the decision to measure particlelike or wavelike properties were made after each photon had interacted with the beam splitter. Consequently the photon could not have been informed at the crucial moment of interaction with the beam splitter whether to behave like a particle and take one route or to behave like a wave and traverses along two routes. The choice of path did not become definite until the measurement was made. The same result also holds for electrons and other subatomic particles. The concept of a path only has meaning at the act of observation. This experiment confirmed Wheeler's choice--the choice now determines what we mean by the past. The electron simply does not exist in the ordinary sense of the word until it is measured. It is our choice now that determines what the past was.
this website is a fascinating article to read, and there are lots more accounts of this experiment. Do your own search, it has come to be known as "The Alley, Jakubowicz, and Wicks Experiment"
I just have to comment on that now Darklord It's kinda fun if you think: because we observe the particle, it exists in a certain way. If we hadn't observed the particle what would it be?? Would it be?
There is this famous story about a cat in a closed box. I don't remember it exactly. Someone shoots the box or something, and the cat isn't alive or dead unless you open the box. Something like that, anybody know the whole story? Was a great analogy.
It seesm kinda silly - if we are not sure if light is a wave or a particle - to come up with an experiment to prove one or the other, or both
if we dont know if light is a particle, then how do we know how wide to open a slit so that only one photon goes through?!
and shouldnt it be a hole, not a slit?! maybe two photons are getting through above/below each other?
This demonstrates one of the problems I have with subatomic particle science - we cant see the things cause they are shorter than light waves, so they cant reflect light
so we have to make assumptions ontop of assumptions - and then about 4 or 5 assumptions (theories) down the path something really weird happens, and we have to come up with a bizzare explaination.
Maybe its because we really dont know whats going on at all?
Originally posted by Ken Wittlief: It seesm kinda silly - if we are not sure if light is a wave or a particle - to come up with an experiment to prove one or the other, or both
What are those little novilty thing you can get that have a little spinny thingie in them that spins when light hits it?
Originally posted by Ken Wittlief: It seesm kinda silly - if we are not sure if light is a wave or a particle - to come up with an experiment to prove one or the other, or both
if we dont know if light is a particle, then how do we know how wide to open a slit so that only one photon goes through?!
and shouldnt it be a hole, not a slit?! maybe two photons are getting through above/below each other?
This demonstrates one of the problems I have with subatomic particle science - we cant see the things cause they are shorter than light waves, so they cant reflect light
so we have to make assumptions ontop of assumptions - and then about 4 or 5 assumptions (theories) down the path something really weird happens, and we have to come up with a bizzare explaination.
Maybe its because we really dont know whats going on at all?
Well, we know it's just one photon, cause photon's have a certain amount of energy and energy we can measure.
I don't know what you mean by the difference of hole/slit, but like I said, if we can measure the energy of a photon we can say for certain how many photons went through...
Originally posted by 84Bill: What are those little novilty thing you can get that have a little spinny thingie in them that spins when light hits it?
Whats pushing on the spinny thingie?
Or what about the "Solor Sail"?
got to have substance to "push" something
It doesn't mean that light can not behave like a particle! It sometimes does as was proven by that experiment. It can also behave like a wave. When pushing the thingy, I would imagine a photon (as a particle) flying against the sail and "pushing" it.
but how do we know the energy of one photon is we dont even know what a photon is?!
maybe photons always travel in groups of 3?
the thing bill is talking about, with the white/black diamond panels in a vacuum bulb
if light is a particle, then why does it go right through the solid glass, but it hits the black metal plate and makes that spin?!
I think I said this once before - particle physics is like trying to figure out how a fiero works, but they are so small you cant even see them, so we accelerate fieros up to high velocities then crash them into each other
and measure the energy of the particles that fly off
for all we know a single hydrogen atom could be as complex as an entire universe.
Discussing Quantum Physics on monday morning - this is cruel!
Originally posted by Ken Wittlief: but how do we know the energy of one photon is we dont even know what a photon is?!
maybe photons always travel in groups of 3?
the thing bill is talking about, with the white/black diamond panels in a vacuum bulb
if light is a particle, then why does it go right through the solid glass, but it hits the black metal plate and makes that spin?!
I think I said this once before - particle physics is like trying to figure out how a fiero works, but they are so small you cant even see them, so we accelerate fieros up to high velocities then crash them into each other
and measure the energy of the particles that fly off
for all we know a single hydrogen atom could be as complex as an entire universe.
Discussing Quantum Physics on monday morning - this is cruel!
Well, we don't even have to argue about photons, cause maybe they're made of 1-dimensional strings! And what about quarks? Every particle, like a proton, neutron etc. is made of 3 quarks again! How did we find that out? Like you said, bumping them into eachother fast enough, with enough energy, so that quarks came out of that! Do we know quarks then again are the smallest particles in the universe? No, we don't, we don't have a fast enough particle accelerator to measure this. But that's the problem with Quantum physics, we go beyond the Planck-length. String theory argues something totally different. Quantum physics uses point particles, string theory uses one-dimensional strings. If you use string theory, everything starts making more sense, and we don't get the weird stuff we see in quantum physics.
[This message has been edited by Screwie (edited 01-14-2002).]
Originally posted by 84Bill: What are those little novilty thing you can get that have a little spinny thingie in them that spins when light hits it?
Whats pushing on the spinny thingie?
Or what about the "Solor Sail"?
got to have substance to "push" something
THE BLACK&WHITE SPINNERS are moveing by heating up a little air inside the glass on the black side if a nearperfect vacume is made inside the glass bulb the spinner doesnot spin at all.
PHOTONS have no rest mass BUT DO HAVE ENERGY when moving and E=MCsqd so a very small mass when in motion.
IN THE CAT RIFF there was no cat no box or a 1/2 DEAD CAT it is just a thought exparement about how to understand a 1/2 dead cat state of what IF this then that IN THE REAL WORLD no cat canbe 1/2 dead but in quatum state the math works to describe a unreal unmessured state of problemablity.
WE ARE STILL WORKING WITH STONE KNIVES AND BEAR SKINS give it some time like a 1000 years for real answers we do not know the real questions yet.
Originally posted by ray b: THE BLACK&WHITE SPINNERS are moveing by heating up a little air inside the glass on the black side if a nearperfect vacume is made inside the glass bulb the spinner doesnot spin at all.
What about a solor sail? no air in space to expand, no air to resist movement either. and whats this thing called "Solor Wind"?
[This message has been edited by 84Bill (edited 01-14-2002).]
Originally posted by Screwie: Well, we don't even have to argue about photons, cause maybe they're made of 1-dimensional strings! And what about quarks? Every particle, like a proton, neutron etc. is made of 3 quarks again! How did we find that out? Like you said, bumping them into eachother fast enough, with enough energy, so that quarks came out of that! Do we know quarks then again are the smallest particles in the universe? No, we don't, we don't have a fast enough particle accelerator to measure this. But that's the problem with Quantum physics, we go beyond the Planck-length. String theory argues something totally different. Quantum physics uses point particles, string theory uses one-dimensional strings. If you use string theory, everything starts making more sense, and we don't get the weird stuff we see in quantum physics.
[This message has been edited by Screwie (edited 01-14-2002).]
some versions of strings theory say all matter is made of the strings AND ONLY DIFFERENCE is how they move, rotate, spin, vibrate, or tumble and at what speeds and direction of same. THATS eazy enuff but then they add extra dimensions to make the math work right 11 or 14 extra.
Originally posted by 84Bill: What about a solor sail? no air in space to expand, no air to resist movement either. and whats this thing called "Solor Wind"?
[This message has been edited by 84Bill (edited 01-14-2002).]
SOLAR WIND is not ONLY light but bigger stuff thrown out by sun like atoms and parts of them by H-BOMB like condishions inside sun pure lite is only about 0.001% of power of total power of flying stuff in solar wind
Originally posted by ray b: some versions of strings theory say all matter is made of the strings AND ONLY DIFFERENCE is how they move, rotate, spin, vibrate, or tumble and at what speeds and direction of same. THATS eazy enuff but then they add extra dimensions to make the math work right 11 or 14 extra.
Well they do have to add extra dimensions to get them to work right, like I said already. But it's not so much to make the math work, as that when they do add these extra curled up dimensions, the strings can vibrate in a way, that the respective charges/spins etc of the particles we see (which are the strings) are exactly the way they are when found through practical experiments. Very exact. They even found some theoretic values for particles which can't be tested yet, but when used in theoretical physics, they make a lot of sense in further calculations! In a way, as you say, it is a kind of "simple" idea, although working it all out is much harder. But the fact that it seems kind of simple makes it even more intriguing
Just another thought here. The little spinny thingie will spin with a flashlight. I don't feel heat from such a small device and it certainly ain't barfing out atoms like an h-bomb.
Originally posted by 84Bill: Just another thought here. The little spinny thingie will spin with a flashlight. I don't feel heat from such a small device and it certainly ain't barfing out atoms like an h-bomb.
In a high school phy class many moons ago the teacher had a globe riged to a vacume pump to show if all most all air is pumped out it willnot spin at all.but let some air back in and it will spin!!! heat is the source of spin if air is in globe heat infra-red goes thru glass fine thats why a greenhouse works.
BACK TO EARTH SUCKING as per last weeeks science news mag 3% of all matter is stuff we can see 30% is thought to be dark matter 67% is now thought to be DARK ENERGY SO WHAT IS DARK MATTER? or DARK ENERGY we donot know YET but 97% of everything is missing from sight by current MATH or maybe we have the wrong #'s in the calculations.
