Path Time Paradox

[TheReasonWhyGuy]

I don't think the issue is time making sense... I think it's our understanding of photons.

Also, it's a question of, can field probabilities allow a photon to move across a distance, whilst traveling at the speed of light, and travel a greater distance than it's speed alone would allow.

[Boehoehuahoei]

Well photons can be detected. And photons never become waves. Sometimes (like in the experiment) u get a wave like result. The problem with this experiment is. that when u go to check the hole the photon went through the interference pattern disappears. And at that point u have a completely different experiment. so the result is different. In this case i would say. that u may have 2 different answers (1 for each hole). but. since am measuring it . the result will probably be different.

[Boehoehuahoei]

Well its the same paradox u had to begin with. Since your specifying a photon, its a particle. so it can have to different times, either one hole or the other. If ur not specifying a particle u'll get a wave. and then u'll have the canceling each other out principle .

[SalixAlba256]

Should we think of a photon as a wave packet rather than a point. So the front edge of the packet will hit a screen slightly before the rear of the packet. This would make the notion of exact time of arrival somewhat vague.

Grebo from UKC

[tusvanhoon]

No paradox. for the single photon experiment whether or not an interference pattern emerges depends on the coherence length of the photon source. for lasers, short pulses correspond to shorter coherence lengths as they are made up of many frequencies which move out of phase as they propagate. a continuous beam is very coherent and is composed of relatively few frequencies. how coherent the source is will depend on the level transition that emits the photon and the uncertainty relations.

[dndn1011]

Since the experiment requires coherence anyway, I don't see your point. Also "short pulses" is meaningless to a stream of photons. You are not actually explaining anything that addresses the actual paradox. See my other video "Delayed path interferometer" to understand the paradox that I am actually describing.

[tusvanhoon]

in the video you said the photon was emitted at time T.a (how do you do subscripts in these?). But how certain are you of this depends on the photon source. if you are very certain (you are using the transition of a very unstable excited state to some ground state of an atom) then our uncertainty ΔT is very small. now by our uncertainty relation ΔE ΔT > h/2 we would know that ΔE is relatively large. since the energy of photons is directly proportional to the frequency the uncertainty in the

[tusvanhoon]

{continued from above} frequency of the photon ΔF is then also relatively large. If that is the case then the photon is comprised of many frequencies and is not coherent so we do not get any interference pattern. You will find that the interference pattern will only emerge when ΔT becomes large enough to allow for the possibility that the photon could have traveled though either of the slits.

[arjenvreugd]

Light is a wave phenomenon. A wave cannot be instantaneous but is by its very nature spread out in time and space. A definite interference pattern requires light of a definite frequency, which requires a pulse lasting for several periods.

If you emit a brief light pulse, there will be no interference pattern but only a bright spot. There is no paradox because both slits give the same path length.

If you emit a longer pulse, it is no longer possible to tell when the photon was emitted.

[dndn1011]

I think you are missing the point. There is no length of time. Photons individually are instantaneous. Light appears to behave both as a wave and a particle (this is called wave-particle duality). Even if you subscribe to the idea that a photon is a wave function that collapses, the problem is that time paradoxes remain. Check out the links I added for an explanation of this. The key thing I am pointing out is that "which way?" is not the only mistery... "which time?" is as well.

[arjenvreugd]

The paradox arises because you think of the light as consisting of photons localized in time. They aren't; the incoming beam is a constant prob. function. The same is true after the slit.

Quantum physics says you can't find out when exactly a photon passes each slit; as soon as you measure at the slits, the pattern disappears.

Finally, recall Heiseberg's time-energy principle. If you can tell how much photon energy hit the screen, you can't tell when: ΔE Δt > h/2.

[dndn1011]

Although you are apparently correct in what you are saying (although I have to check the Heiseberg's time-energy principle), this does not help: it is clear that we can fire a photon at a known time and detect it at a known time (otherwise we cannot measure the speed of light by measuring the time delay). The question is, which time? If we are able to measure the time and this was to tell us which slit the photon went through, then there would be a whole lot of trouble. So I argue that...

[dndn1011]

if we do measure the time, then it can tell us nothing about which hole the photon went through. Indeed, I am arguing that the photon does not have a path, or exist in time. I avoid the paradox by saying "classical time and space has no relevance to a photon".

The questions remaining are: what would be the experimentally measured time and the validity of the Copenhagen interpretation if the concepts of time and space do not apply to a photon. See "Delayed Path Interferometer part 2"

[cyberdems]

Very interesting! A paradox indeed, until a solution (which obviously must exist) is found. This may very well be used as some form of 'evidence' catalyst in further understanding how photons work and the nature of this weird physical universe...

[roblowe777]

Plus, sound is just a small alteration of the Higgs field i.e. the Higgs field resonating, not creating a massive ripple in the Higgs field as the CERN experiment will do.

[dndn1011]

I had the opportunity to see the detector at CERN in December, most impressive. I am not sure if the experiment will help much in answering the question I pose here, although please fill me in, I am always eager to learn more :)

[roblowe777]

Question: If you are inside a dark room i.e. no light at all, you know there is a table and chair in this room but even when you open your eyes you cannot see it. When the light goes on you can see it, is this because the illusion of the chair is actually coming from the light source and the matter of the table and chair from the Higgs field. This would explain everything using only two phenomena of science .... continued ...

[dndn1011]

Not sure what you mean, I am not familiar with the Higgs field. But the only reason you can see the chair is because you have a lens in front of your retina and have learned from experience that photons hitting it can only come fromone direction.

[roblowe777]

The answer is: light travels instantaniously as far as it is concerned. We live within a Newtonian Physical world and see it travel slower. This is just a Newtonian world illusion of observing the quantum world. The answer is the path is quantumly instantanious and we observe the weirdness in a Newtonian sense. You can observe quantum systems if you like as a different dimension, the dimension within which time travel is possible - i.e. light travels instantly within its understanding of all.

[dndn1011]

It is a possibility; but it does not answer what an experiment would actually measure,but is my point: there is a big problem no matter what the answer is :)

[jakabob199]

Let me try to resolve ur issues with quantum mechanics:

Quantum theory (and all scientific theory) is a mathematical tool. A tool which tells you what to expect given a physical situation (or experiment). This is the ONLY sense that any physical model is 'true'. You are trying to make sense of the interpretation of these models such as what it means for a photon to 'travel'. Unfortunatly, quantum theory does not go with logic & intuition, so you run into problems.

[jakabob199]

To emphasise this point:

The only sense that a photon 'truly' travels, is that if we desribe its travel through a model (such as saying it travels as a probability wave) then we will get correct experimental answers.

What this means for the meaning of reality is something i can't help you with!

I hope my comments are helpful. Enjoy philosophising!

[dndn1011]

Well it seems like the experiment should be conducted to find out ! :) thanks for your comments.

[jakabob199]

I believe the answer to the "exam question" would be that you not measure a single time for everytime the photon landed at point B (nor would you measure the 2 times that it would take through each seperate slit, at random). Instead, the measured times would fit onto a gaussian curve, with the variation and mean etc.. determined by the distance between slits, frequency of light and where point B is.

[jakabob199]

The 'reason' for this is that the photon travels as a probability wave. These are altered by the slits and interference occurs. The result is a system for working out the probability that a photon will arrive at any given point at any given time.

I believe if you look at only the times when it arrives at point B, you will get the probability distribution that i have described above.

"Light travels as a wave, but leaves and arrives as a particle"

[SABRESTR]

This is like time travel paradox, I believe I can just explain this as "alternatives", the photon you detect at point A, and that travels through p1+p2, will be the first alternative, and the photon goes through p3+p4 will be the other alternative, and you only detect one because you see only one alternative, the alternative observer on the other hand might detect the other alternative photon....

[dndn1011]

The problem with that idea is that if you measured the photon time, you would then expect to see two different times at random... this would be an unexpected result. I think the experiment would show the time as constant :)

[SABRESTR]

I think there is nothing random in my theory, what I suggest is, there are alternate realities and they follow a strict pattern and you can not switch between them, plus we have no idea how speed of light or/and time is defined in those alternates. So that photon might actually be going through the first path and in the other alternate time/reality, it goes through the other path.

[EstebanChurches]

I'm a laboratory chemist not a physicist but I did study physics in college. Have you tried to calculate how long it would take the photon, as a wave, to reach point B? Different wavelengths (oscillations) might account for different times of arrival, as well. Me thinks :-D

[dndn1011]

Good thought, but light takes travels at the same speed in a vacuum regardless of wavelength, so it should make no difference.

[kardel100]

thats all well and good but does light travel lite or take an extra suitcase for the return journey?? nice to see you again D, i know someone that will try to answer that question for you but chances are you will both be still discussing it in 3 light years from now!!! lol take care buddy Derek

[b1heqh54]

It's always been my understanding that observing the photon in order to calculate the elapsed time to reach the target changes the observed effect such that the impact point would no longer fall between the two slits as in the diagram, but instead would fall directly behind one slit or the other. The observed interference pattern associated with the wave hypothesis is replaced by a distinct two band distribution by the act of observation. I too look forward to a hopefully more informed answer.

[dndn1011]

What you are suggesting is that if a device to measure the time of impact of the photon were set up,it would destroy the interference pattern; this does not seem plausible. Why should measuring the moment of detection change the behavior of the light? If it did this would be a staggering result. In a sense any photon detector would also be detecting the precise moment of detection as well position of detection in any case.

[gemberkoekje]

I know that generally in quantumphysic-thinamy the whole idea is that you can't measure time without changing place, and you can't measure place without changing time, which is the general paradox.

However, if this idea is true, would that mean if there would be 1 slit or no slits at all one would still detect a photon at the end?

[dndn1011]

Yet any photon detector must detect both position and time (the time of detection). WHat you are refering to is something different: you can't know the position and momentum of a particle precisely. The point with the photon is that (I argue) it has no momentum. The moment it is detected it is "destroyed".

[b1heqh54]

More staggering yet, if the decision to to observe is delayed and the observational data is looped until an unrelated decision variable goes high the resulting pattern can be controlled independent of time. There are more conventional sources for you to explore, but I did find a couple of vids here on YT that provide a summary of past experimental results. /watch?v=_OWQildwjKQ and /watch?v=QBOaXcG3sJ0&featu­re=related

[dndn1011]

Such thoughts lead to "Conciousness Causes Collapse" :)

[b1heqh54]

I think we're on the same wave :)

[malfattimusic]

or maybe not, i just play guitar and sing songs....its heavy stuff here dino....lol

[malfattimusic]

does light always travel at a fixed speed? maybe when the photons hit the barrier the speed changes slightly.