adding time of flight measurements to double slit experiment

rge

ith

slit)

ing behind the other slit.

slits)

s constant x frequency.

ETECTION issue.

and electrons bound to those.

we

t

ide quoted text -

It's wave propigation between the source and detector. Mind you this is my interpretation of what Phil said. For myself, it's all spooky and it's good to focus on what you can measure.

George H.

ETE=3D

an=3D

mething happens

mage a bit.

t office

ing 'sci.physics'

got some reward

ot expect to see

to work WILL be used.

well be the mosquitos

station for weeks.

nds with current theory.

ures (for example 'photons particles of light' is

carried away by the same

es, and you will outpace all of them

he desktop, then you cannot do it with a machine the size of the universe'.

? (what is it that waves)'.

in and out of existence',

ere was a theory called 'epicycles'

omoting clan of 'scientists' could do the calculations and understand it.

it giving the right answers.

rk 'rework' your math (as we see in LIGO looking for gravity waves).

the candy).

the brain dead do not wake up again likely.

play an other one on the poor kids that perhaps are to come.

Hmm, OK, how about just looking at what can be measured. You are pretty good at that.

e

but waves at many wavelength, and amplitudes.

We send the light through a narrow band 'green' interference filter. As you turn down the voltage on a light bulb it gets redder and redder. You can find a spot with few green photons. It works pretty well. Not my idea at all.

d my views on those experiments by now.

, must die before we see the rising sun of common sense again.

sation, the Roman civilisation,

Geesh, I'm just not that negative about the current understanding. Science is fun! No?

George H.

behind the other slit.

constant x frequency.

DETECTION issue.

electrons bound to those.

quoted text -

It may be wave propagation, but the fact you can use QM effects to image an object without any photons hitting it is something that cannot be explained with classical physics.

--
Dirk

http://www.neopax.com/technomage/ - My new book - Magick and Technology

Phil is absolutely right. The only way to understand any of this modern physics is through the mathematics and testing those predictions against reality. Natural language is far too ambiguous to make any progress.

something happens

a bit.

More anti-semitism rears its ugly head. Get over it. Einstein managed to do enough major work to qualify for Nobel Prize and bar.

office

What are you raving about?

Actually it demonstrates tremendous inginuity. Leading quantum mechanics researchers are now building microscopic versions of device to exploit second order correlation effects in the same way that Hanbury Brown & Twiss did for astronomy with their intensity interferometer in the late

1950's. A talk from not long back at the Royal Society shows some of this work in outline (NB not a native English speaker the start of the talk he says "increasing flux" when he really means waiting for longer at constant flux until the total number of photons has built up to reveal the pattern). This should be a direct link to a talk on cutting edge experimental quantum entanglement research (if it doessn't work go to Royal Society and search webcasts).

Snip a lot more inane drooling and whining from another anti-Einstein mathematically illiterate nutter.

Regards, Martin Brown

Please learn to *READ* and understand the vocabulary! I said

*indistinguishable* if I had meant identical I would have said that.

Identical path length is the condition for the white light fringe which is unique. Most interferometers satisfy the roughly monochromatic criterion of bandwidth/frequency or are split into subbands that do allowing a reasonable variation of path length.

There must be at least two ways for the wave/particle to travel and reach its target for fringes. Light explores all possible paths all the time, but the only ones that do not correspond to geometrical optics path of least time solutions all cancel out. The aperture interference patterns are a manifestation of the wave nature of light, but you can just as easily make silver ions or buckyballs diffract with a suitable target.

But as soon as you can (even in principle) determine the path taken by a photon it no longer interferes with itself through the other slit. The time gate would give you some photons that go through the kit faster than the assymetric long path but they would only show a diffraction pattern characteristic of the width of slit that they passed through. Crucially there would be no fringes until after there had been time elapsed sufficient for both paths to have been traversed.

Regards, Martin Brown

On a sunny day (Tue, 31 May 2011 13:44:00 +0100) it happened Martin Brown wrote in :

I will not bother to read your link. The fact that I disagree wit hEinstein makes me anti-semitic? You are the one who is insane. (not that I like Jewish policy and Israel one bit, they do every thing they ever accused the Germans of, except the Germans never used organs from innocent children they shot. the Germans only occupied Europe for maybe 4 years, the Israelis keep Palestinians in camps for tenth of years and daily kill some. That place Israel will soon find its end, it's enemies are coming together, US no longer gives a shit unless they comply with 1967 borders. So, tale that. One should look at Einstein and his 'success' in the context of the politics and powers of that time.

Only way to understand it is math? Maybe for a brain dead moron like you and you retarded friends.

You are to0 brain dead to even see you fell of the road and just keep wading in the mud. It will get deeper and dirtier and swallow you.

I will not interfere. Good riddens,

On a sunny day (Mon, 30 May 2011 16:56:06 -0700) it happened John Larkin wrote in :

The most beautiful thing that De Broglie writes here is where he says: page 21 etc. And explain the random element if QM as the interaction with basically a (very complex) ether. Derived from 'Brownian motion', well just read it.

You should then also look up the videos on the web of the Feynman lectures, where he (Feynman) draws on the blackboard the path particles take, then divides it into subpath particles *could* take, and basically ends up with the QM equations and explanation of the interference. It is almost if Feynmain --- IT IS that Feynman does not give the REASON, and De Broglie mentions the reason, the ether, that the particles take so many path. I am talking about the 1979 Douglas Robb memorial lectures by Richard Feynman. I do not have a link, but google should show them, they are free to download. I think these are the names of the files:

517457346 2009-06-11 15:40 electrons_and_interactions.avi 498481258 2009-06-11 15:41 fits_reflection_transmission.avi 409850990 2009-06-11 15:42 photons_corpuscles_of_light.avi The last one I have is 'todays answers to Newstons queries about light'. 498147728 bytes 2009-06-11 1. I am not sure if these are the original file names, I sometimes rename them so I can find them back, I have all that stuff under 'edu'. Could be that last filename is 'what_where.avi' or something.

So you are wrong. :-)

On a sunny day (Tue, 31 May 2011 00:33:45 +0100) it happened Dirk Bruere at NeoPax wrote in :

something happens

But Maxwell used fluids to build his equations. They assume some ether, matter.

something happens

And Einstein assumed spacetime. However, the primacy of mathematics over intuitive mechanical models started with Maxwell's equations.

--
Dirk

http://www.neopax.com/technomage/ - My new book - Magick and Technology

complex) ether.

divides it into subpath

explanation of the interference.

I like this one, relates to the futility of trying to find "reasons" ("mechanisms") of fundamental forces in terms of everyday things (which are *themselves* the result of those very same forces you are trying to explain)

path.

498147728 bytes 2009-06-11 1.

I can find them back,

[...]

--

John Devereux

The TOF histogram will have two spikes: one at T1, and another at T2. Each photon took one path or the other.

Any given photon is monochromatic.

But you can figure out which slit it passed through after the fact, by measuring TOF. Well, as long as the path lengths are different enough to resolve the TOF.

John

Hi,

What about the case where light is used to push matter but not change the orbital states of electrons? For instance a coherent light source laser, with standing waves of light used to hold matter in one place? When the light wave crests in these cases push on matter, with no quantum orbital changes, yet work is still being done, where are the photons?

cheers, Jamie

Only in "Larkin World".

I believe you are dead wrong. If you could by any means determine afterwards which slit the photon had come through even in principle (never mind the practical difficulties) then the interference pattern will be destroyed.

If you think you can demonstrate the opposite or know of an experiment where it has been done then it is Nobel Prize winning stuff!

Absolutely untrue. Any given photon is localised in space and time and as such it *must* have a non-zero full width half maximum in the frequency domain. A perfectly monochromatic wave would have to be infinite in extent. The only thing that is to an extremely good approximation monochromatic is coherent laser light.

There are people using two photon processes to fire triggers and so modulate the wavefunction of the second emitted photon eg.

No you can't.

As I explained above and you totally failed to understand if the time is too short for the longer path to have been traversed at the speed of light then any photons you detect will show only the diffraction pattern of the slit that they passed through and *NO* interference fringes. If you think you can do it then show me the experiment!

Regards, Martin Brown

Copenhagen

I posited a beam splitter interferometer because it would be easy to measure the path lengths. It would be difficult to resolve the prop delays in a 2-slit setup. But the principle is the same: the photon takes one path or the other, and a detector can tell you which it took. All the probabilities, all the multiple universes, are collapsed by the act of detecting the photon.

It's simple to demonstrate, as long as you have the equipment to make short light pulses and a fast photodetector and oscilloscope.

Fire a fast pulse of light from a laser, and trigger the scope. Route the light through any confusing path of slits or beam splitters, into a detector. Pretty obviously, the scope will display a spike for each of the beam paths. A pulse of laser light is just a lot of photons.

Just because you are confused, the photon's aren't.

Ever hear of Planck's constant? A photon carries some amount of energy. Given that, the Planck equation lets you compute its wavelength. There's only one answer. Well, as long as you believe Planck and conservation of energy.

You are confusing a beam of light, a statistical collection of photons, with one photon. One photon is monochromatic. And it's not infinitely long.

There's no reason, in principle, why you couldn't have a gadget that emitted photons regularly, at exactly the same wavelength. But nothing associated with that gadget, or its output beam, need be infinitely large.

As noted, all you need is a pulsed laser, a photodetector, and a scope. And some collection of beam splitters, mirrors, slits, whatever that creates an apparently ambiguous path. But, as I noted, it's hard to confuse photons.

John

s to a

ticed the

travel

light

for the

source,

ing

light as

ight is a

openhagen

y do

ul to

er, or

ll

ility

r r

he

a n

me.

ow or

there

, then

cluster

e

gram

alls

an

oint

tion

e.

ce

k h

rference fringes =A0

one

ly

ly

ic

n.

Hi John, I think you forgot about the uncertainty principle. There's an uncertainty in your energy answer that depends on your time uncertainty. But it's nothing magical for photons, just Fourier analysis. A really small frequency uncertainty means a wave that goes on for a long time.

George H.

it

ak

he

you

te.

a n

source,

as

Copenhagen

Conservation of energy does not hold at the quantum level on short enough timescales. You can borrow energy from the vacuum provided that you give it back quickly enough. How else to you think virtual particle and virtual photon pairs come into existence? And their properties can be measured experimentally see Casimir effect.

For this level Wiki is perfectly adequate in its description.

No it isn't. For heavens sake! Get a *clue* and stop demonstrating such wilful ignorance of mathematics and physics. Heisenberg long since formulated the Uncertainty Principle for conjugate variables related by the Fourier transform which becomes dominant in the quantum world:

delta_x*delta_p >= h/2pi delta_E*delta_t >= h/2pi

Just like with the second law of Thermodynamics not only can you not win but you cannot quite break even either. Knowing one accurately necessarily trades knowledge of the other and vice versa.

There, is but you clearly do not understand the mathematics. Why I am not surprised that you prefer bluff and bluster to mathematical proof?

Clearly you didn't look at this link. It demonstrates one of the tricks that is being done to modulate the wavefunction of a secondary photon emission with a controlled pattern.

You choose to remain ignorant. That is your problem.

There are experiments under way to try and demonstrate wave and particle properties simultaneously along different paths. I happen to think that they might one day be successful and that in some as yet unseen way "particleness" and "wavefunctioness" are also manifestations of a deeper universal conjugate variables symmetry that parallels that of energy,time and position,momentum etc. The latter view is pure conjecture but I reckon more than a few theoretical physicists do consider it a possibility. Multiverses are another way of fixing things up but that solution also leaves a lot of loose ends.

Regards, Martin Brown

a

the

travel

light

the

source,

light as

is a

Copenhagen

or

then

cluster

fringes  

I don't understand that.

All the t-e uncertainty principle says is that it takes time to accurately measure the energy of a photon. Not that the energy itself varies with time, which would violate COE.

I'm not a physicist or a philosopher, I'm an engineer. I can and do measure optical time of flight, and I know that having multiple paths through an optical system results in multiple times of flight, and classical physics and geometry predict the TOF. It works for big optical pulses, so it must work for single photons. The photons do not get confused, and the TOF histogram does not smear out into some fuzzy continuum, because QM exists.

John

the

the

source,

as

a

Copenhagen

cluster

The question was: given a beam-splitter interferometer with unequal legs, and a detector exposed to both beam paths, and the capacity to measure time of flight through the system, what will the TOF histogram look like? Simple experiment, clearly measurable results.

I contend that there will be two distinct TOFs observed, corresponding exactly to the path lengths, as classic physics would predict. You seem to think that the quantum uncertainty of the paths will somehow smear out the discrete TOFs into some sort of indistinct mess.

If single photon TOFs are smeared such as to modify the double-spike histogram, then big laser pulses must be similarly smeared by the quantum/path uncertainty, since even a kilojoule light pulse is made of photons.

But that doesn't happen.

John

ents to a

noticed the

to travel

f

the light

ay for the

ght source,

veling

he light as

e light is a

e Copenhagen

ally do

seful to

igger, or

ecall

bability

ee.

1 or

nser

ut

e the

as a

oton

time.

indow or

if there

its, then

ne cluster

wo

take

stogram

d balls

u can

e point

unction

ing

hem

so

in

arge.

ource

look

he

with

one

nterference fringes =A0

alone

g

cally

vel

2. > >> >> Each photon took one path or the other.

t

isely

ctric

tron.

d

's

" I don't understand that. "

Sorry, I'm not very good at explaining things.

Photons are just like radio waves, so lets talk about those.. (if that's OK)

Say, you've got a 1 MHz oscillator. You make this into a 1 second pulse of RF by gating it on and off. (It it's now a pulse 3 X 10^8 meters long.) What's the frequency? Is it 'exactly' 1 MHz? If I send the pulse into a spectrum analyzer will I measure a finite width?

It says a bit more than that. It's not that the energy varies, it's just uncertain. If a photon has a finite lenght/ time then there is an uncertaintly in the measurement of the photon energy. If you want to 'think' about the photon as having some exact energy, and we just can't measure it. Then I believe that is OK, we can have all sorts pictures about things (photons/ electrons), but in the end we can only agree on what can be measured. (That's the beauty of science after all.)

George H.