robinpike

 

No. Because the photon does not have a valid frame of reference.

 

 

No. Because the photon does not have a valid frame of reference.

 

 

Possible. Perhaps inevitable that some light from the Earth will be moving parallel to some light from a distant star, I suppose.

 

 

There is no connection between them. Why should there be? And as neither of them are in a reference frame, then they cannot be in the same one.

 

 

I kind of see what you are thinking now. It is wrong because there is no reference frame. It is also wrong because, even if that were a valid reference frame, it would just be one of an infinite number for every possible direction that light could move in. And these would all be different for different observers.

 

So, in at least three ways: not a reference frame and not absolute.

This is good - I now understand the replies to my question.

 

So the only way for you to accept you are wrong is if it is shown another area of physics is wrong?

 

Are you saying that the two photons are travelling at "c" relative to an absolute frame and everyone measures the speed of light to be "c" relative to this absolute frame regardless of their speed relative to the absolute frame?

 

Or are you simply mocking people on this forum by perpetuating a ridiculus notion that if a is true b must be true with no logical reason to support it.

 

Two photons are moving side by side therefore the Moon made of cheese!

I'm not sure how that has been concluded from my question?

My question was: if two photons are moving side by side, are they in the same reference frame?

Or the other way to ask the same question: if two photons are moving side by side, is it possible that they are not in the same reference frame?

The reason for wanting the answer agreed to that question, is because of this observation...

Two photons moving side by side need not have originated from the same point in space and time. For example, a photon from a star a thousand light years from us, reaches us and as it passes by, we can create a photon such that the two move side by side with each other.

So in that situation, assuming the answer to the question above is that they are moving in the same reference frame, what is the connection between how those two photons have been created?

So getting back to my opening question: Is it possible that these two photons were created against the same reference frame? And then, since there is nothing special with how those two photons were chosen, does that mean that all photons are created against the same reference frame? i.e. an absolute frame of reference?

The inconsistency that I am focusing on is this:

Using an experimental set-up of say photons and a barrier that always absorbs photons (rather than the option of reflecting them), such as a barrier coated in carbon black, these experiments can be performed.

1) As a test to see if the photons are ever able to pass through the central part of the barrier between the two slits, a complete barrier (without any slits) is set up to that thickness and the photons fired at the barrier to see if any photons pass through the barrier or are reflected. For arguments sake, we will take it that the results are that no photons passed through the barrier and very few photons were reflected, the vast majority being absorbed by the barrier.

The conclusion of this first experiment is that, whether the photons are moving as particles or as waves, they are never able to pass through a barrier of that thickness.

The second conclusion is that, if a photon collides with the barrier, then it is typically absorbed by the barrier, and only as an exception is it reflected.

2) The next experiment is set up to see how many photons are able to collide with the barrier at a very shallow angle and not be absorbed. For arguments sake, we take it that with the rough surface of the carbon black, say only 1% of the photons are reflected.

The conclusion of this second experiment is that, the after just a couple of multiple collisions with the barrier, all the photons will have been absorbed by the barrier.

3) Now we do the double slit experiment with the central barrier between the two slits is set to the thickness as used for the above, and the depth of the barrier itself being many times that thickness.

If the photons are passing down the slits as waves, then how do the photons make it through the slits without touching the walls of the slits and avoid being absorbed?

For the QED explanation of the pattern of the photons on the far detection screen, is that the photons, on exiting the slits interfere with each other's paths. This implies that the photons (whether as a wave or as multiple paths) while travelling down the slits would have encountered the walls of the slits at some point - and therefore be absorbed.

So the question is, if the interference is because the photons are waves, then the explanation is inconsistent with the photons being able to get through without being absorbed by the sides of the slits?

 

You've effectively uncoupled the argument, then. You can't completely get rid of motion, and time passes. So what?

 

It does not follow that motion is necessary for the passage of time.

But that surely is the point, time is only present when there is motion?

How can it be possible for time to exist without motion?

Maxila, you have asked some very valid questions in your posts here.

 

I understand frame of reference as meaning a set of coordinates that allow me to make measurements of position, direction, and changes to those under time. What do you understand frame of reference to mean?

 

You are imbuing frame of reference with properties and characteristics (an almost concrete existence which an object either has to be within or not) that the standard definition does not include.

I appreciate that I am probably not using the term correctly.

I am trying to argue that, because light moves at a constant speed in all frames of reference, this means that light must first be moving at a constant speed to a 'universal frame of reference', as a first requirement to produce that result.

Detecting such a 'universal frame of reference' is another question, and shouldn't be used as a blocker to stop the first point being discussed / decided.

 

First of all the frame of reference in which the observation is made is one we are at rest in, the speed of light measured in this frame is always c, regardless of which frame you choose to make your measurement in. If light travelled relative to a universal frame we would measure the speed of light to be other than c in the frame in which we make the measurement. This is the principle of relativity. You are the one making unecessary additional (universal) frames.

 

Second, you ask

 

"if two photons are travelling side by side how can this not lead to the conclusion that they are travelling relative to a universal frame"

 

My question to you would be how does it lead to the conclusion there is a universal frame? Does it lead to any conclusion? Can you disprove a negative or just collect enough evidence to show a diferent answer is more likely?

 

Thirdly, This universal frame you are insisting on must by definition be absolutely at rest, what is the frequency of light in this frame. We know the speed of light is constant in all frames but its frequency changes depending on your motion relative to its source so what would the frequency of light be in a universal frame, zero or infinite?

 

(keeping wiht the theme)

 

Fourthly, the point everyone is trying to make is that two photons travelling side by side does not lead to the conclusion there is a universal frame nor does it lead to the conclusion there is not a universal frame...

 

But everthying else we know tells us there is not a universal frame, as many people have explained in many different ways.

Perhaps it would help if I reverse the question...

If two objects are side by side, and remain so, is it possible that they are NOT in the same reference frame?

If it is possible that they are not in the same reference frame, then I will re-assess my conclusion.

 

What's the reference to this experiment? (Journal, date, page number, etc)

 

 

I don't think QED will give you the answer you are naively expecting.

 

I don't know the journal reference, but Richard Feynman knew about the experiment as he refers to its results in his book 'QED The Strange Story Of Light And Matter', on page 21 in the Introduction.

"As we continue to substitute still thicker layers of glass - we're up to about 5 millionths of an inch now - the amount of light reflected by the two surfaces reaches a maximum of 16%, and then goes down, through 8%, back to zero - if the layer of glass is just the right thickness, there is no reflection at all. (Do that with spots!)

With gradually thicker and thicker layers of glass, partial reflection again increases to 16% and returns to zero - a cycle that repeats itself again and again (see Fig. 5). Newton discovered these oscillations and did one experiment that could be correctly interpreted only if the oscillations continued for at least 34,000 cycles! Today, with lasers (which produce a very pure, monochromatic light), we can see this cycle still going strong after more than 100,000,000 repetitions - which corresponds to glass more than 50 meters thick. (We don't see this phenomenon every day because the light source is normally not monochromatic.)"

My issues with QED still stand when considering either experiment...

With the partial reflection of light from glass:

1) The reflection from the front surface occurs at a different time to when the 'reflected' light from the back surface returns to the front surface - and so a single photon cannot be using the QED mechanism.

2) QED mechanism does not explain how partial reflection can be 'turned off' or 'amplified', for example, zero partial reflection.

And with the two slit experiment:

If either of the two slits is closed, then the number of electrons / photons reaching the screen is halved. This shows that half of the electrons / photons were passing down that path. If a barrier is used that absorbs the electrons / photons if they reach any part of the barrier, then QED is inconsistent in when it treats the electron / photon as a particle, and when it treats the electron / photon as a wave.

1) When travelling down a slit, QED treats the electron / photon only as a particle - for if the electron / photon were a wave at the point of entering the slit, or during its passage down the slit, then what would stop the wave from touching the sides of the slit and the barrier absorbing the electron / photon?

2) How is it that only once the electron / photon emerges from the slit that QED then treats the electron / photon as a wave?

 

So you are looking for philosophy, not science. Try two doors down the hall on the left.

Not really...

Those were simply examples to show that a valid calculation can fail as an explanation.

The QED explanation using multiple paths is shown to be false by the experiment - that is science...

QED states that the cause of the variance in the partial reflection of light from the front surface of the block of glass is as a result of multiple paths.

This hypothesis can be tested by using a very thick block of glass, as now the probability of the multiple path from the back surface of the glass becomes an insignificant contribution towards the interference.

But the experimental results do not bear that out - as a one centimetre block of glass behaves no differently to a 10 metre block of glass.

Perhaps it would help if someone could calculate the QED probability of the multiple path that is reflected from the back surface of the glass, when the block is 10 metres deep, and when the block is one centimetre deep?

For QED to agree with experiment, that multiple path probability has to be the same for the two different blocks of glass.

Thanks

Multiple paths are not the reason; they are a way of describing the reason. The reason is non-locality.

 

"Multiple paths" and the calculation in QED is just a way of accounting for the nonlocality of quantum effects.

 

How else would you quantify the effect of everything in the universe, other than by summing every possible path and interaction (with the appropriate weighting).

 

It is like the way any sound can be represented by the (weighted) sum of sinewaves of different frequencies. The more frequencies you include (with ever smaller contributions) the more accurate your representaiton will be. That doesn't mean that a car engine has an infinite number of sinewave generators. Similarly, I wouldn't say the ,multiple paths are real.

 

 

As the theory works and you are therefore wrong, your points are not valid.

No - just because the calculations work, doesn't mean that the theory is valid as an explanation.

For example, the movements of the planets around the sun can be calculated accurately using formulae based on the planets being black holes - such an approach works but isn't a correct explanation of reality.

The confusion arises when the terms 'calculation' and 'theory' are innocently treated as having the same consequence.

For example, the Law of Gravity (a set of equations) allows us to calculate how bodies with mass influence each other - but having those equations doesn't allow us to explain gravity, it doesn't explain the mechanism of how gravity works. It doesn't even allow us to understand what mass is.

Strange, I appreciate your input.

The problem is that the idea of multiple paths being the reason for the variation in the amount of reflected light from blocks of glass of different thickness - is that it doesn't hold up to close scrutiny.

My points above stand as valid reasons why.

 

I don't see why the many paths explanation isn't equally applicable to that: you consider all the paths taken. "Proceeding side by side" is irrelevant because the outcome of the double slit experiment can be changed by things that happen after the interference pattern is formed (the delayed choice version of the experiment). So timing is irrelevant.

 

We know (from theory, from experiments like this, and entanglement and ...) that quantum effects are inherently non-local in both time and space. They are affected by things that happen elsewhere and in the past and the future.

 

That is why the QED calculations work: every path and every possible interaction has to be considered because it will have an effect on the outcome. At the simplest level things that are closer (the other side of the galss) will be more significant than, say, reflection off the surface of Pluto next Tuesday.

I didn't know that the QED calculations included paths that exist at different moments in time?

So the probability of any one path is not just related to how far away the path is from the 'overall path', but also how far the path occurs in the past or the future?

As an explanation, QED is sounding more and more far fetched ! So now it involves time travel ?

 

I don't see why the many paths explanation isn't equally applicable to that: you consider all the paths taken. "Proceeding side by side" is irrelevant because the outcome of the double slit experiment can be changed by things that happen after the interference pattern is formed (the delayed choice version of the experiment). So timing is irrelevant.

 

We know (from theory, from experiments like this, and entanglement and ...) that quantum effects are inherently non-local in both time and space. They are affected by things that happen elsewhere and in the past and the future.

 

That is why the QED calculations work: every path and every possible interaction has to be considered because it will have an effect on the outcome. At the simplest level things that are closer (the other side of the galss) will be more significant than, say, reflection off the surface of Pluto next Tuesday.

The above fails...

When the block of glass used in the experiment is say 10 metres thick, the interference from the path that comes from the back surface of the glass, the above says that path would be negligible - as it is so far away (and so far ahead in the future !)

And yet, when the experiment is performed, and a millionth of an inch is shaved from the back surface of the glass, the amount of reflected light from the front surface changes.

 

 

Why does "the photon takes all paths, and most of them interfere and result in no signal" not work as an explanation?

The 'many paths' explanation is plausible for the double slit experiment, since there the 'interfering paths' of the single photon progress side-by-side and so can occur and overlap at the same time.

However, for the partial reflection of light from a block of glass, the 'interfering path' that comes from the photon reaching the back surface of the glass and being reflected back, that path returns to the front of the glass at a different (later) time - and so the reflected path from the back of the glass cannot interfere with the reflected path from the front of the glass.

This means that the amount of light reflected from different thicknesses of a block of glass, for example it can vary between 0% to 16% depending on thickness of the glass, must have a different explanation to the 'many paths / interference' explanation offered by QED. (Even though, as a calculation, QED agrees with experiment.)

The variation in the light reflected from the block of glass experiment, suggests that there is something varying (I don't know what) with the atoms in the block of glass, and it is this that is involved in the reflection of the light, and the variation in the 'whatever' depends on the thickness of the glass.

 

Have you watched the Feynman lectures on QED yet? He covers this in great detail.

Yes, the QED calculations are covered in detail, and I have no problem with their accuracy and ability to agree with what is observed.

I'm just saying that QED doesn't appear to work as an explanation. If someone could explain how it works for a single photon (in terms of this discussion), I would much appreciate it !

If the response is going to be: it is not possible to explain - QED works as a calculation, the calculation is all that is required of Physics?

That is okay, but it should be clearly stated that QED is just a means to calculate, and QED is invalid as an explanation...

 

Yes, but as you say that's interference and depends on some of the wave traveling through the material and reflecting.

But that explanation based on interference fails to work when the experiment is performed with individual photons.

When the experiment is performed with individual photons, and the amount of light returned from the front of the glass is counted over time, it is found that the amount of light depends on the thickness of the glass.

An individual photon cannot interfere with itself through reflection from the front and back surfaces of the glass - as by the time the 'reflection' from the back surface reaches the front surface, the photon is no longer there.

 

The electron (or photon) interacts with the electrons in the material of the barrier. This is what makes the barrier opaque to electrons/light.

 

I second the recommendation for Feynman's lectures. He explains some of the subtleties very clearly.

When the experiment is performed with NO slits in the barrier, the electrons / photons never get through to the other side, the barrier is opaque to the electrons / light.

So, when the two slits are present in the barrier, and the wave meets that small part of the barrier that divides the two slits, how does the wave manage to progress?

Why isn't the wave absorbed by that part of the barrier?

Imatfaal, I don't mind referring to the analogy of the water wave to help the discussion, but my questions always refer to the behaviour of the electron / photon.

You mention that the water wave does not go through the barrier - I accept that.

But my question is why the electron / photon wave does not go into the barrier? What is stopping the 'quantum wave' from passing through the inside of the barrier as it is passes down each slit?

Unable? No. While water, specifically may not have been observed, atoms and molecules have been. My graduate work was in this field. I work next door to a guy who observed sodium atoms and dimers interfere. It's been observed in C-60 (buckyballs) and that was 15 years ago!

http://physicsworld.com/cws/article/news/1999/oct/15/wave-particle-duality-seen-in-carbon-60-molecules

 

To paraphrase Josh Billings, there is a problem here with the things you know that just ain't so.

 

 

It's the wave explanation. The wave goes through both slits.

Yep okay, fair point about the atoms and molecules.

What I want to understand is how the wave explanation (for example for the electron) describes the path of the wave as it travels between the two slits.

For example, is there any time when the wave is inside the small part of the barrier that divides the two slits?

If the wave does spend some time inside the barrier that divides the two slits, I don't understand why the wave doesn't collapse? Or if it doesn't collapse how the wave is able to progress while inside the barrier?

If the wave does not spend any time inside the barrier - then I don't understand what is preventing the wave from taking that path?

 

Saying that there is no partial reflection of the individual quanta is a different argument. No, there is not, because there are quantized properties that you can't split up. Just as individual water molecules can't be partially reflected, and yet water waves exist.

 

Electrons and photons can be reflected and more importantly can diffract and interfere, which are wave properties.

Analogies have to be used with care ...

True, the path of a single water molecule is never partially reflected, but on the other hand, a single water molecule is also unable to interfere with its own path.

So when the experiment is done with discrete photons / electrons over time, what is the explanation for how the photon / electron interferes with itself?

Both the wave explanation and the multiple path explanation, have difficulties.

 

Electrons (and photons) are quanta or fundamental. Part of the electron or photon cannot be left behind.

 

When you consider light classically, then clearly some will get through the slits, some will be absorbed and some reflected. But any individual photon (or electron) can only follow one of those routes ... with a probability that reproduces the classical distribution.

If the electron / photon only follows one route - how does the interference occur?

 

And yet that's precisely how they behave, which has been known for >75 years.

But they don't behave as waves!

We know that they don't behave like waves by the example of waves in a water tank...

A water wave never passes through the wall - only through the gap. When the part of the wave meets the wall, that part is reflected back.

Electrons and photons are never partially reflected back - they are either completely absorbed by the wall / completely reflected by the wall, or they are completely able to pass through the slit and appear on the other side.

The failing of the many paths route / wave explanation, is that for all the possible paths that put the electron / photon at some point inside the wall - that will stop the progress of the electron / photon completely.

 

Electron/positron annihilation doesn't have the energy to create a neutron, by a factor of almost 1,000.

 

There might be instances that are consistent with it, but a refutation requires you look at all the evidence. All you need is one counterexample to refute an absolute, i.e. the idea that something cannot happen, or something must happen.

 

e-e+ annihilation does that.

I meant that the neutron is an example of a neutral particle that has charge inside it, showing that a neutral particle in itself is not proof that the charge no longer exists.

On that basis, therefore it does not follow that the e-e+ conversion into neutral photon / photons is proof that the charge has been 'destroyed'.

Is there any other evidence that supports the hypothesis that charge - and + can be destroyed?

Total charge is the conserved quantity. Asking if it "goes anywhere" might lead one into a misconception that charge is a "thing" rather than a property of the system. A system with zero charge, i.e. neutral, can mean nothing in the system has any charge, or that there is an equal amount of + and -.

 

We know the individual charged particles disappear because we stop detecting them, e.g. in a cloud chamber. The tracks stop (or in pair production, start) and you get tracks from charged particles. We can also detect the gammas from the pair annihilation showing conservation of momentum and energy, but nothing else is detected.

Thanks

However, neutrons don't leave tracks in a cloud chamber, and yet they have positive and negative charges inside them (with the charges being on the quarks).

If someone were to think that individual amounts of charge cannot be created or destroyed, are there other pieces of evidence that could be used to refute that idea?

There are two slits. A wave will pass through both and interfere with itself. A particle will pass through only one slit.

 

If the experiment is set up so that you can tell which slit each photon passed through, there will be no interference pattern. If there is no way to determine which path each one took, there will be an interference pattern.

Treating the electrons as waves seems to be a rather implausible explanation!

When the electrons are fired with the apparatus having NO slits present, the electrons never get through the barrier, they never appear on the other side.

From this, it can be concluded that the electrons are not able to pass through the barrier.

With the proposed explanation when the two slits are present in the barrier, is that the electron is a wave, or the electron 'travels' along many paths and those different paths enables the electron to interfere with its own direction of movement when it exits on the other side of the barrier.

If the electron really were a wave, then part of the wave will always be inside the interior of the barrier, where the electron / wave would not be able to proceed, and it would become trapped inside the barrier.

Or, if the electron were travelling along many paths, then most of those paths would also take the electron into the interior of the barrier, and the electron would not be able to proceed, it again would become trapped inside the barrier.

How can the electron as a 'wave', or as a 'particle' able to travel along 'multiple path', ever manage to make it to the other side of the barrier, regardless of whether the slit is present or not?

 

The mass has been converted into some other form of energy. Photons, for example, or kinetic energy of some other particle.

 

The charge has not gone anywhere, as it's a conserved quantity. If a +1e particle annihilates with its -1e antiparticle, the net charge is zero, both before the interaction and afterward.

 

These are properties of things, not things unto themselves.

Swansont, that line could be interpreted in two ways...

1) The TOTAL charge has not gone anywhere, as it's a conserved quantity.

2) The INDIVIDUAL charges have not gone anywhere, as they are a conserved quantity.

I assume that you mean that the total charge does not go anywhere?

But individual charge can disappear as long as an 'opposite' individual charge also disappears at the same instant?

Just out of interest, how is it proved that the individual charges have disappeared?

Or the converse, how is it disproved that the individual charges are present?

Thanks

In addition to the equations not making sense, they are consistent with everything else that's known about photons, and there is no way in which such a reference frame makes physical sense.

 

Think of what it means to have an observational frame of reference, and I suspect that anything you think of will not apply to a photon.

 

All lengths contract to zero in the direction of travel, so they can't measure length. All trips would take zero time, so there is no way to measure travel time. A photon's state doesn't change from emission to absorption, ie. it doesn't age, ie. it measures no passage of time. A photon doesn't absorb other photons, so it can't observe anything while traveling. To accelerate to c requires infinite energy, unless you have no mass, but if you have no mass then you have no rest energy, so you can't be at rest and you can't have a rest frame. All these things fit together, and there's nothing that describes a photon being able to observe. The math models physical reality, and the math doesn't work for a photon's frame of reference, while there is also no such thing known or theoretical that makes sense to model.

But this assumes that light and matter are fundamentally the same...

Yes, all the above probably does apply to matter - but why does it have to apply to photons?

 

How can you have a universal frame? That implies one single frame of reference. But there are an infinite number of frames that give you this answer.

 

Plus, as you've been told, there is no frame of reference for photons.

Yes, different frames for different observers - but for the photons themselves, do they move relative to their own universal frame?

If they do not move to a universal frame, how can the following be explained...

Using starlight thousands of years old and created in a different part of the galaxy to us, if it happens to reach us, then we can create some light and compare the two by directing the newly created light so that it is moving parallel to the path of the older starlight. If we were to do this, then we would find that the new light moves at the same speed as the old light.

How is this result explained if light does not move to a universal frame?