Observers

[danshawen]

I was just thinking, if I could flip the spin of an electron faster than light I could build a clock that has a frequency beyond measurement!

But I don't believe it's possible. Such a clock wouldn't be very useful, either.

It might have unintended causal limitations.

Fortunately, time dilation allows this limitation to be easily sidesteped. Everything in the universe shares the quantum field instant of now, but after that, it proceeds at different rates. Part of your gate could be at 1 m from the surface of the Earth, the other at 2 m. It would make a big difference. Problem solved!

 

[arfa brane]

It might have unintended causal limitations.

Yes. For instance explaining how it's possible for a system to change state such that the laws of physics are violated.

Fortunately, time dilation allows this limitation to be easily sidesteped.

Well, maybe, but locally it can't make a difference. Clocks are defined locally, right?

Everything in the universe shares the quantum field instant of now, but after that, it proceeds at different rates.

Sorry, I don't understand that at all.

Part of your gate could be at 1 m from the surface of the Earth, the other at 2 m. It would make a big difference. Problem solved!

So you're saying I can send a signal a distance of 1m that tells my gate to flip the spin of an electron, and I can do this FTL?

 

[danshawen]

Sorry, I don't understand that at all.

There is a big difference (infinite, actually) between an instant of time and an interval of time. This was basically Minkowski's mistake, which makes no difference for a complete description of bulk energy propagation <=c. An interval of time may be proportional to a velocity, but an instant of time may not.

A single instant of time, from moment to moment, is the same throughout the entire quantum field that permeates the universe. If this were not true, a particle with quantum spin = 0 would be impossible. That instant of time or spin = 0 needs to be referenced to something, and this much is shared with the theory of Special Relativity. Since a quantum spin = 0 exists, and the entire universe is not spinning (and you could easily tell if it was), QED.

This is why quantum entanglement is at once the basis of the instant of now, and also the only thing faster than the propagation of light in a vacuum, and also the reason light is ABLE to propagate at all. If the velocity of the propagation of light were the basis of time itself, it could not propagate. We know that photons can be entangled, and this alone suggests the basis of time is something other than the propagation of light.

Circular polarization (entanglement) proceeds as the waveform unfolds and propagates, but this is not a mechanism that is limited by a time dilation that is infinite as relativity would predict. This is a gaping hole in relativity theory that needs plugging.

It's all there in the cracks between the science that is known for certain, if you only take the effort to reason it out.

 

[arfa brane]

A single instant of time, from moment to moment, is the same throughout the entire quantum field that permeates the universe.

That's something which if true, is impossible to demonstrate.

If this were not true, a particle with quantum spin = 0 would be impossible.

The Higgs boson is spin 0.

That instant of time or spin = 0 needs to be referenced to something, and this much is shared with the theory of Special Relativity. Since a quantum spin = 0 exists, and the entire universe is not spinning (and you could easily tell if it was), QED.

How is it that an instant of time is spin 0? The Higgs field is scalar, there is no spin direction and only one spin state. There is nothing to reference because the Higgs field is isotropic.

If quantum spin was equivalent to instants or intervals of time the universe would have different physical laws, surely?

This is why quantum entanglement is at once the basis of the instant of now, and also the only thing faster than the propagation of light in a vacuum, and also the reason light is ABLE to propagate at all.

You're confused about what entanglement is, as I said earlier.
When you entangle two particles, it constitutes a measurement which is not classical (you get them to interact, but you don't do anything else which is "observational"). That's why entangling is called quantum measurement.
You have a measurement basis, where time is locally defined. You don't have a basis for the "instant of now".

 

[danshawen]

How is it that an instant of time is spin 0? The Higgs field is scalar, there is no spin direction and only one spin state. There is nothing to reference because the Higgs field is isotropic.

Great questions, all.

If you are an expert on superposition of quantum states, then you understand that a spin=0 boson would need to be the superposition of a boson that has a positive spin with a boson that has negative spin in precisely balanced equal magnitudes. The Higgs boson is an excitement of the Higgs field. It is a property of the Higgs field that it endows an excitation with spin = 0. Even in classical mechanics, angular momenta are easily superpositioned. Why should quantum spin superposition work any differently? Even a quantum spin must be relative to something not spining (=0 angular momentum).

Because the inertia it imparts is given in every direction at once, the Higgs mechanism would seem to require entanglement in order to accomplish what it does.

This description meets the criterion that the Higgs field is entangled everywhere. In other words, the field does not have linear inertia, but evidently it has spin inertia, or else it could not produce a spin=0 particle that interacts to give inertial mass (in EVERY direction at once) to things like fermions (which have ± half integer or fractional spins), and itself.

If quantum spin was equivalent to instants or intervals of time the universe would have different physical laws, surely?

The rate at which quantum spin "direction" may change is equivalent to the smallest incremental instant of time, not a time interval, and not an artifact of the spin itself. Notice, this definition of time is completely independent of any variable having to do with space, or the propagation of bulk energy in space.

Don't believe I have explicitly said that before. It's the explicit statement of the model I'm working from.

You have a measurement basis, where time is locally defined.

Defining time (intervals, dilation) locally is a fine idea, but an entanglement spin flip is not subject to time dilation as time intervals are, because it requires no interval of time, t=0, in order to flip. Nor does it require a convoluted theory of spacetime for bulk energy propagation v<=c.

 

[arfa brane]

Defining time (intervals, dilation) locally is a fine idea, but an entanglement spin flip is not subject to time dilation as time intervals are, because it involves no passage of time to flip.

I don't think that's correct. You can flip the spin of an electron with a photon of the right frequency. You can change the polarization angle of a photon (i.e. its spin) by getting it to interact with matter.
Flipping a spin vector involves a rotation of the (abstract) Bloch sphere of directions, this can't be instantaneous because the Hilbert space is physical.

 

[arfa brane]

What kind of gate is a pair of rectangular slits?
When does it "go quantum"?

You have a beam of electrons, say, beams of electrons have been around since Maxwell. A beam of electrons is classical, it has an energy, a temperature, even a pressure. Each electron has an average velocity, and momentum, hence average energy; the average energy per particle is the temperature of the beam (ask an LHC tech).

But, upon reaching the pair of gaps in an otherwise impenetrable barrier (earthed, to prevent classical charge building up), the beam undergoes diffraction, and it looks very similar to what you see if you use x-rays instead. It looks similar if you 'capture' the emerging beam with film, that is.
Of course, it all needs to have very small dimensions, the wavelengths involved are way beyond visible light.

So, anyhoo, the beam diffracts and there's an interference pattern immediately. The classical input has become something else, and we already know the same result is given one particle per time interval (one-particle inputs). All that is possible because of the advances in technology that have given us the means to fabricate the very small diffraction grating (with only two apertures).

But, we know we have to explain what happens between the grating and a screen in terms of wavelike behaviour and superpositions. The electrons, or other particles, can't reach the screen instantaneously.

But, the interference pattern is there because of constructive and destructive superposition. This superposition must be the same wavelike pattern for each electron, otherwise the pattern on the screen wouldn't have any phase-relative information in it. The superpositions must be the same in space and time, so the determining agency of the position of dots must be the Uncertainty Principle 'acting' on momentum. QED.

So, when does this 'fixed' superposition of states appear for each electron? Is it when the beam leaves the emitter? When particles (even one) reach the double slit? Or is it there before you even do the experiment??

 

[arfa brane]

I think I'd like to go with the second option; you need to set the experiment up but then you need to beam some classical electrons as inputs, into the apparatus.

The way the Bloch sphere canonically represents the spin of a spin-1/2 particle, as the incommensurate measurement of spin in the z direction with either the x or y directions, can be taken to any pair of incommensurate variables like position and momentum. How to think about it though?

The Bloch sphere is a space where a measurement basis can be in superposition, in a direction orthogonal to the basis.

 

[danshawen]

What kind of gate is a pair of rectangular slits?
When does it "go quantum"?

It isn't the slits that "go quantum". If you arrange to direct entangled photons at it from the same source (a pair of entangled electrons, then it goes "quantum". Observing electrons passing through either slit causes the diffraction pattern produced by both to decohere. Add different amounts of delay to the slits causes the diffraction pattern to decohere faster than light can propagate the path between the two entangled photons.

The two slits interfere with each other in the same way even if only one (unobserved) photon goes through at a time. That's "going quantum" as well. An instant of time is a sort of a quantum specialty for anything that is entangled. Of course it produces an interference pattern even one photon at a time.

Using a beam of electrons instead of photons with the double slits actually might not produce the same results. It might leave a residual electric charge on the double slits. Could be messy to predict what would happen after that.

The superpositions must be the same in space and time, so the determining agency of the position of dots must be the Uncertainty Principle 'acting' on momentum. QED.

The uncertainty principle works just fine here mainly because both the atom(s) generating the entangled photons and the barrier of which the slits are made are constructed of matter. The position of a photon passing through one slit or the other makes physical sense. Its velocity is always the speed of light. A wave-like treatment of the photon will give its velocity. A particle-like treatment will give a position.

o, when does this 'fixed' superposition of states appear for each electron? Is it when the beam leaves the emitter? When particles (even one) reach the double slit? Or is it there before you even do the experiment??

No, it isn't there before you do the experiment. It's there whenever a pair of entangled electrons or charges emit a photon.

Again, with electrons the double slit experiment is going to be double tough. Use photons.

Photons and a beam of electrons can actually have the same energies, but one would be charged and the other not.

 

[arfa brane]

It isn't the slits that "go quantum".

Hold up. In QM you shouldn't say things like that, it makes you look like you think you understand it.

I think myself that the two slits in a double slit look like a spatial kind of function, which has a time-domain representation (which I happen to know about, and which is used in filter design).
However this function is classical.

Perhaps there is some kind of entanglement going on, between the two slits, which you could say each particle gives a single measurement of.

That is, each particle is measuring an amount of phase-shift, defined physically by the slit dimensions, and the particle wavelengths so it must be the same phase-shift.

Notice how much the notion of a particle has changed, in the last 100 years or so.

 

[danshawen]

Hold up. In QM you shouldn't say things like that, it makes you look like you think you understand it.

I think myself that the two slits in a double slit look like a spatial kind of function, which has a time-domain representation (which I happen to know about, and which is used in filter design).
However this function is classical.

Perhaps there is some kind of entanglement going on, between the two slits, which you could say each particle gives a single measurement of.

That is, each particle is measuring an amount of phase-shift, defined physically by the slit dimensions, and the particle wavelengths so it must be the same phase-shift.

Notice how much the notion of a particle has changed, in the last 100 years or so.

Sorry about that. I don't really uderstand all of it either. I suspect, as you probably do, that the double slit experiment is showing us as much about atomic structure as spectroscopy does. That's where Pauli's exclusion principle came from, and that in turn is why we know as much as we do about electron configuration of atoms. I do recall, this level of certainty about something as small as an atom really fascinated me as a child.

I get carried away sometimes when I recognize that combining ideas about relativity with entanglement seems to have the potential to nudge science just a few notches deeper into nature's grand plan.

The one thing about which I am certain is that quantum physics discarded the variable for time like a used handkerchief when they found that proportional math with time as proportional to a velocity didn't work. Instead of revising their ideas about time, they took to gaming science with probabilities because those almost never went to zero. I'm not impressed by this compromise. It's time we put time back into those equations. An instant of time allows both conservation of energy and entanglement in one bold conceptual stroke, and even suggests another force at work to bind particles of matter together. The last time that happened, we got E= mc^2 in the bargain.

 

[Confused2]

Imagine a 'quantum clock' - (doesn't matter how) that ticks at some sensible and reasonably predictable rate. Now make another totally entangled with the first one (still doesn't matter how). Place one at a lower gravitational potential than the other. I think QM says they have to tick at the same rate regardless of GR and GR says they have to tick at different rates regardless of QM. Would QM or GR win?

 

[Q-reeus]

Imagine a 'quantum clock' - (doesn't matter how) that ticks at some sensible and reasonably predictable rate. Now make another totally entangled with the first one (still doesn't matter how). Place one at a lower gravitational potential than the other. I think QM says they have to tick at the same rate regardless of GR and GR says they have to tick at different rates regardless of QM. Would QM or GR win?

As soon as a single measurement is performed on one part of an entangled system, the state changes and entanglement is broken thereafter. Now translate that to your hypothetical 'entangled clocks' scenario. Each measured 'tick' represents a new system state. Still think there is some clash between GR and QM via 'entangled clocks'?

 

[danshawen]

Imagine a 'quantum clock' - (doesn't matter how) that ticks at some sensible and reasonably predictable rate. Now make another totally entangled with the first one (still doesn't matter how). Place one at a lower gravitational potential than the other. I think QM says they have to tick at the same rate regardless of GR and GR says they have to tick at different rates regardless of QM. Would QM or GR win?

Just the question is golden. I'll have to think about it, but as far as entanglement phase lock goes, I think it is likely they still run at different rates. If they did not, the famous relativistic pi meson experiment would not have worked. Even mesons produced by cosmic rays are clocks.

It really is imperative that relativity agree with quantum mechanics for the latter to go forward. If they can't be reconciled, one of them will need to go or be modified in a more drastic way.

 

[danshawen]

http://physicsworld.com/cws/article...ks-could-provide-accurate-world-time-standard

The idea evidently is to remove GR from clock synchronization, eliminating a lot of more complex calculations and measurement of satellite relative velocities via Doppler shifts. Entanglement synchronization would assuredly be simpler than those kinds of periodic corrections.

Simpler is always better, even if it is not always possible or practical. I can think of a few reasons this might be impractical to implement in a global network.

Availability of such a system certainly would have eliminated the OPERA FTL neutrino fiasco.

 

[arfa brane]

Entanglement synchronization would assuredly be simpler than those kinds of periodic corrections.

It's as simple as being able to communicate an entangled state.

Entangled clocks don't use entanglement to keep time, the atomic clock part does that. The entanglement and its communication between clocks is the resource the system of clocks can use, to synchronise with each other in a more reliable way than sending a classical synchronization signal.

The news article in your link is about an idea to upgrade the GPS system, basically with clocks which are also quantum computers. Essentially it would be a distributed quantum computer, which finds a solution to a synchronization problem. On the face of it it seems like an obvious thing to do, except quantum computers aren't really here yet.

And the authors suggest the system of clocks arguably would be a gravitational wave detector, that's if the many technological problems can be overcome. I understand someone has demonstrated entangled synchronization of atomic clocks already.

 

[arfa brane]

Back to what the double slit experiments mean.

Two slits mean a particle has a complex probability amplitude for the path it takes (through one or both slits). Does one slit mean it has an ordinary probability amplitude--of 1--for its path?
The interaction of a particle with one slit must be characteristically the same kind of interaction with more than one slit, except less complicated.

Consider ordinary surface waves. Where these meet a barrier they reflect, but if there's a small opening in the barrier, part of the wavetrain propagates through it.
You notice that the wavefronts propagating through the opening are not unaffected, they gain some sideways velocity as each wave leaves the slit, and the emerging wavefronts are circular.

A particle propagating through space with velocity v has a deBroglie wavelength in the direction of propagation given by $$ \lambda = \frac {h} {p} $$.
Along a wavefront which is propagating in one direction, the wave isn't 'moving sideways' anywhere, but this sideways momentum is a consequence of the wavefronts interacting with an opening in a barrier with the right kind of dimensions (not too small nor too large).

 

[arfa brane]

Why is it that wavelike motion can be described in two dimensions? That is, you can define a system of wavefronts the same distance apart, along a two-dimensional slice of an actual system of wavefronts such that each slice is perpendicular?

We can take images like these, in other words, and describe them mathematically so we get a close approximation, a mathematical physics of wave motion:



There are various aspects of what the images represent. For instance, you could consider them in a signal processing context (notice how the right hand image has a smoother output than the left), or in the context of uncertainty about wavelength, and so on.

Notice the 'sideways' motion from each edge of the slits (the apex either side of each slit acts like a point source of waves with a lower amplitude) . . . hmm

 

[arfa brane]

The topic then, what is an observer, goes to what is information, and eventually what is a quantum interaction such that entanglement exists?

As to what entanglement is, the answer appears to be we don't know yet. If we did know we would understand the black hole information paradox and what the physics is that relates gravity to the quantum realm, i.e. we would have a theory of quantum gravity. We do know that this theory will depend on some entanglement measure or metric, however.

So we already have something that outputs or appears to output, something we don't understand completely, which we call entanglement. We know it has an informational structure because it only emerges when measurements are made, so it seems to be the key, or part of a key, that will unlock deeper relations between information and quantum fields.

 

[danshawen]

The topic then, what is an observer, goes to what is information, and eventually what is a quantum interaction such that entanglement exists?

Notice how direction specific entanglement is. Pairwise, it is something that acts only between pairs of points along paths connected by photon travel time at any range from zero to the span of the known universe, and nowhere else. This is the principle reason why any observation of entanglement effects always entails a choice of direction. No intelligence is necessary for an observer or an instrument to observe entanglement effects other than a choice of direction. The double slit is the perfect example of this. A choice of observing one slit or the other amounts to a choice of direction in which to observe.

As to what entanglement is, the answer appears to be we don't know yet. If we did know we would understand the black hole information paradox and what the physics is that relates gravity to the quantum realm, i.e. we would have a theory of quantum gravity.

We will never have a satisfactory theory of quantum gravity until or unless it includes a mathematical description of that phenomenon that does not include the assumption that any point in inertialess empty space is the origin of a coordinate system.

The inertial roadbed of the Lorentz transformation needs infrastructure repair that includes tearing out the origin coordinate markers on the side of the road, as well as the delusion that a moving frame that contracts as it moves can have an origin permanently anchored to the center of a meter measuring stick and expect that space as defined by classical greek solid geometry belongs anywhere in a relativistic universe where only energy transfer events and time exist.

The only absolute time is the instant of now in an all pervading and universally entangled quantum field. The only absolute space is at the geometrical centers of the composite bound particles of energy we refer to as matter or antimatter. The speed of light is not the basis of time, and the speed of light itself is invariant and relative to an invariant and all pervading quantum field whose relative motion to anything else is not defined because the only inertia it really has is related to zero quantum spin and entanglement. The universe as a whole is not spinning, and if it were, you would immediately notice this as something wrong.

Making the speed of light the basis of time only happens when an interval of time is equivocated to an instant of time, and this is a proportional math equivalent of division by zero, a serious mistake that has retarded physics models for over 100 years now and restricts a physical description of reality to a consideration of proportional velocities <= c. Depending on your point of view, entanglement can be viewed as faster or slower than c. Slower or faster, like any other relative velocity, is relative to the reference frame of the observer.