The Universe is Deterministic

[Tumbleweed]

Your question is not stated clearly but:

We do not just see the "only a billion year old light". We see the light from all ages of the universe from about 377,000 years after the Big Bang.

Remember that the speed of light means that looking out into space is the same as looking back into time, e.g. we see Alpha Centuri as it was 4 years ago.

You also seem to be assuming that the processes that were producing light a billion years after the Big Bang created a flash of light and then stopped. This is not the case.

I think you misunderstand me. Lets say two stars have formed and accelerated to a point one billion light years apart after the big bang. One of them goes super nova and will represent an early event in a young universe. If that light from the super nova goes past the other star in one billion years, and since no matter could possibly catch up with the super nova light, how is it to ever be seen again by anyone?

 

[Reality Check]

I think you misunderstand me. Lets say two stars have formed and accelerated to a point one billion light years apart after the big bang. One of them goes super nova and will represent an early event in a young universe. If that light from the super nova goes past the other star in one billion years, and since no matter could possibly catch up with the super nova light, how is it to ever be seen again by anyone?

That is right - the light that passes the other star from the supernova will not be seen again at that star and no one at the star will be able to catch up with it.
Of course the light can still be seen by someone at other stars further out from that star and attributed to a supernova in the young universe.

 

[sol invictus]

Quantum field theory is strictly causal in the sense that no event outside a lightcone can influence any event inside it.

Apart from issues of measurement, QFT is strictly deterministic in the sense that the wave function (which describes the system as fully as is possible) is completely determined by the wave function at an earlier time.

You can verify those statements in any book. While I'm happy to discuss their implications, it's irritating to be challenged on facts about QFT (which, after all, is a theory).

Then you will have to explain your use of “commute” in that context.

I've lost track of what you're trying to argue for or against, so I'll just address concrete questions like that one.

"Commute" refers to a property of operators and matrices. If two operators A and B commute, then AB-BA=0. In relativistic QFT it is a fact that A(x) commutes with B if x,y are spacelike separated. Physically, that means that operations such as creating particles cannot affect anything outside the future lightcone of the spacetime point where said particle was created.

 

[Tumbleweed]

That is right - the light that passes the other star from the supernova will not be seen again at that star and no one at the star will be able to catch up with it.
Of course the light can still be seen by someone at other stars further out from that star and attributed to a supernova in the young universe.

But what if there were no stars further out, that the universe had only spread out a tiny fraction of what it is today. Then the light from an early supernova would quickly catch and pass the accelerating matter, but someone however many years later would have no clue that the early supernova existed because its light is now billions of light years past all matter. There has to be a limit as to how far back you can peek due to the fact that the very early light waves have long since passed us by. Or so it would seem

 

[Reality Check]

But what if there were no stars further out, that the universe had only spread out a tiny fraction of what it is today. Then the light from an early supernova would quickly catch and pass the accelerating matter, but someone however many years later would have no clue that the early supernova existed because its light is now billions of light years past all matter. There has to be a limit as to how far back you can peek due to the fact that the very early light waves have long since passed us by. Or so it would seem

In your scenario (a toy universe with only a star and a supernova) there is only one observer at the star. The "limit as to how far back you can peek" for that observer is as far back as the supernova.
Once the light has passed the star (the "accelerating matter"?) the observer no longer sees the light.

In the real universe, we can peek back to the formation of the CMB, 370,000 years after the the Big Bang. That is because the entire universe was filled with the photons that came to make up the CMB. The universe expanded, the Milky Way formed and the CMB is all around us.

 

[Ziggurat]

Could the wave theory of matter be compared to a game of fish?

Your suggestion would correspond to a "hidden variables" interpretation of quantum mechanics. While not strictly ruled out, the experimental falsification of Bell's Inequality severely restricts the kinds of hidden variables theories which are possible. The ones that remain are... unappealing.

Quantum theory seems to be saying that, sans any other information, where the twin card/particle exists cannot be determined until I guess and the cards are turned over revealing the correct location, and whether my guess is right or wrong.

In the case of entangled particles, we're usually talking about their spin state (because that's easy to correlate between pairs in what is known as a "singlet" state). One can measure other properties of one (or both) particle in the pair without disturbing the spin state of the particle so one can know that the particle exists without disturbing the uncertainty in its spin. Rather than the spin state not existing, however, the math suggests that it exists in all possible spin states simultaneously prior to measurement.

The fact that in the quantum world you either have to have velocity or location but never both

This is not an accurate description of the Heisenberg uncertainty. Consider a fairly localized wave function like, say, a Gaussian. The square of the wave function (which will also be a Gaussian in this case) is basically a probability density. It's got a well-defined average (or expectation) position, but it's also spread out over some area, which corresponds to an uncertainty in position. We can also form a probability density for our particle's momentum, and we will similarly find an average (or expectation) position, but with some distribution that gives an uncertainty to its momentum. So our wave function has both position and momentum (and hence velocity), but because of the distribution in both, it's not a position and a momentum, but more like positions and momentums. The Heisenberg uncertainty principle doesn't say that you can only have one or the other, what it says is that if you take the uncertainties in each and multiply them together, the product has a minimum possible value. But every measurement you ever do, on either position or momentum, will always have some non-zero uncertainty in its result, which means that the uncertainty for the other need not blow up to infinity.

reminds me of pi and its relationship to a circle. You can have a definite diameter but never an exact circumference and vice versa: either one but never both

Um, no. It's NOT like that. Diameter and circumference have an exact relationship, so either you know both exactly or you know neither exactly.

 

[Tumbleweed]

In your scenario (a toy universe with only a star and a supernova) there is only one observer at the star. The "limit as to how far back you can peek" for that observer is as far back as the supernova.
Once the light has passed the star (the "accelerating matter"?) the observer no longer sees the light.

In the real universe, we can peek back to the formation of the CMB, 370,000 years after the the Big Bang. That is because the entire universe was filled with the photons that came to make up the CMB. The universe expanded, the Milky Way formed and the CMB is all around us.

But if the CMB is moving in a straight line at c why are we still detecting it? My only guess is reflection. And what about those eary supernovas/ galaxies. How will we ever detect their radiation or know they existed?

 

[Tumbleweed]

Quote:
reminds me of pi and its relationship to a circle. You can have a definite diameter but never an exact circumference and vice versa: either one but never both


Um, no. It's NOT like that. Diameter and circumference have an exact relationship, so either you know both exactly or you know neither exactly.

I have to disagree with that. I have a circle whose diameter is defined as 5 units. You are telling me you can determine the exact circumference in those same units?? How if pi is not an exact number. Ditto the other way around. I have a drawn circle in front of me. It certainly appears to have a finite diameter and a finite circumference, but mathematically it just does not work out that way. ONE of them has to be indeterminate if the other is defined

 

[Ziggurat]

But if the CMB is moving in a straight line at c why are we still detecting it? My only guess is reflection.

Nope.

I could be wrong about this, but I suspect you're thinking of the big bang in terms of a big empty universe except for a little bit of super-compacted matter which then explodes out into this previously empty space. But that's not what happened. Space itself has expanded. The distinction is important, and if you can wrap your head around it, the rest should fall into place easily.

The CMB doesn't actually originate from the initial bang, but from a time shortly after that when space had expanded enough to become transparent (initially it was full of hot dense plasma). When the universe became transparent, the CMB was let loose into the universe from everywhere, and in all directions. There is no edge to the universe (it's either infinite or it wraps around on itself), so there's nowhere for the CMB to escape, and everywhere we look, we're looking back in time within the universe so we'll always see the CMB.

And what about those eary supernovas/ galaxies. How will we ever detect their radiation or know they existed?

By looking at very distant ones.

 

[Ziggurat]

I have to disagree with that. I have a circle whose diameter is defined as 5 units. You are telling me you can determine the exact circumference in those same units??

Sure: it's [latex]$5 \pi$[/latex].

How if pi is not an exact number.

But pi IS an exact number. It's irrational, so you can't represent it exactly with a finite series of decimals, but pi itself is definitely exact. And you can even write down exact numerical representations of it in a finite amount of space using series.

 

[The Man]

Quantum field theory is strictly causal in the sense that no event outside a lightcone can influence any event inside it.

Technically that simply makes it strictly local or more specifically restricts possible causes and events to time like separations. It in no way imbues any given event or group of events with a cause or group of causes, but simply asserts that such cause or group of causes should be in the past light cone of that event or group of events.

Apart from issues of measurement, QFT is strictly deterministic in the sense that the wave function (which describes the system as fully as is possible) is completely determined by the wave function at an earlier time.

Well of course, any theory or universe becomes “strictly deterministic” apart form the “issues” that make it specifically not, well, strictly deterministic. Just as any universe or theory becomes “strictly causal” apart from that which no strict cause is determined or perhaps can be determined even just within the past light cone.

You can verify those statements in any book. While I'm happy to discuss their implications, it's irritating to be challenged on facts about QFT (which, after all, is a theory).

While I am happy to address or explain anything I have said or mean by what I have said (although I can’t guarantee that such explanation will help either of us), you have simply to ask. However, if you simply choose to make assumptions and irritate yourself there is not much I can or will do about that, except perhaps just irritate you further.

Just as a side note your last remark is a bit confusing. Should not a theory any theory be challenged and how would one go about that without challenging the purported facts about that theory? If you do in fact find such discussions or challenges to be irritating then perhaps you are not as happy to have such dissuasions as you might like to think.

I've lost track of what you're trying to argue for or against, so I'll just address concrete questions like that one.

Sorry Sol, I do not think you were ever specifically on track to what I was saying on this thread and as the writer ultimately the responsibility to make myself clear and subsequent failure to do so falls on me.

"Commute" refers to a property of operators and matrices. If two operators A and B commute, then AB-BA=0. In relativistic QFT it is a fact that A(x) commutes with B if x,y are spacelike separated. Physically, that means that operations such as creating particles cannot affect anything outside the future lightcone of the spacetime point where said particle was created.

Again simply making it local as such a quantization of the field was intended to, not surprising then that it does what it was intended to do.

 

[sol invictus]

Technically that simply makes it strictly local or more specifically restricts possible causes and events to time like separations. It in no way imbues any given event or group of events with a cause or group of causes, but simply asserts that such cause or group of causes should be in the past light cone of that event or group of events.

Yes, I agree. It's a necessary characteristic for causality in a relativistic theory, but it's not sufficient.

Well of course, any theory or universe becomes “strictly deterministic” apart form the “issues” that make it specifically not, well, strictly deterministic. Just as any universe or theory becomes “strictly causal” apart from that which no strict cause is determined or perhaps can be determined even just within the past light cone.

Yes.... but again, the only place where determinism might fail is in this mysterious process of "measurement". If we assume measuring devices are composed of particles that obey the known laws of physics and hence are described by QFT, then there is nothing acausal or non-deterministic there either, except in so far as the MW description itself is.

Whether MW is non-deterministic or acausal is a matter of semantics. It is in one sense (namely that one cannot predict what one will observe in certain experiments no matter how precisely the initial conditions are known), but it is not in another (namely that the full state of the system is determined by its state at any precious time).

Just as a side note your last remark is a bit confusing. Should not a theory any theory be challenged and how would one go about that without challenging the purported facts about that theory?

You can challenge whether the theory is an accurate description of reality, but that hasn't come up much so far. You could also challenge whether some statement about the theory is true. But the statements we've been discussing are pretty basic, so that's going to be tough in this case.

 

[The Man]

Yes.... but again, the only place where determinism might fail is in this mysterious process of "measurement". If we assume measuring devices are composed of particles that obey the known laws of physics and hence are described by QFT, then there is nothing acausal or non-deterministic there either, except in so far as the MW description itself is.

Whether MW is non-deterministic or acausal is a matter of semantics. It is in one sense (namely that one cannot predict what one will observe in certain experiments no matter how precisely the initial conditions are known), but it is not in another (namely that the full state of the system is determined by its state at any precious time).

Well again that is the rub of it Sol “this mysterious process of "measurement"”. Sure it is a matter of semantics; make your definitions broad enough and anything will fit them. We can loosen determinism and/or causality such that if it is so in one sense or not so in just some particular sense then that is good enough. However we could also loosen the restriction on causality from a strict relativistic local only interpretation to incorporate at least some degree of non-locality as long as the restriction on observer to observer non-local communication is maintained. Just as a matter of speculation let’s say in the examples given Alice makes her measurement and it is a result in part due to vacuum fluctuations. As result of her measurement vacuum field along the space like interval connecting the entangled particles is altered. As Bob makes his measurement the state of the vacuum field in the local area of his measurement device has already sifted to ensure a correlated measurement. Basically the vacuum state of the two space like separated locations are said to be ‘Superentangled’ (if I am reading it correctly).

I accidentally posted a link to the wrong paper in post #126 (I’ve just barely started reading that one) it was supposed to be this one, Sorry.




http://philsci-archive.pitt.edu/archive/00000649/00/RS_meets_NW,_PDF.pdf

from the Abstract

The Reeh-Schlieder theorem asserts the vacuum and certain other states to be spacelike superentangled relative to local fields. This motivates an inquiry into the physical status of various concepts of localization.

from the Conclusions

The local fields allow the possibility of arbitrary space-like distant effects from arbitrarily localized actions, equally counterintuitive and equally compatible with Lorentz covariance!

 

[sol invictus]

Well again that is the rub of it Sol “this mysterious process of "measurement"”. Sure it is a matter of semantics; make your definitions broad enough and anything will fit them. We can loosen determinism and/or causality such that if it is so in one sense or not so in just some particular sense then that is good enough.

Well, if there's a standard meaning to "deterministic" in physics it's that the state of the system at time t>0 is completely determined by its state at t=0. QFT and QM in the MW interpretation are deterministic according to that.

However we could also loosen the restriction on causality from a strict relativistic local only interpretation to incorporate at least some degree of non-locality as long as the restriction on observer to observer non-local communication is maintained.

True, but it's very hard (perhaps impossible) to come up with theories that manage that. And it's unnecessary, since MW has no such non-locality and works perfectly well.

Just as a matter of speculation let’s say in the examples given Alice makes her measurement and it is a result in part due to vacuum fluctuations. As result of her measurement vacuum field along the space like interval connecting the entangled particles is altered. As Bob makes his measurement the state of the vacuum field in the local area of his measurement device has already sifted to ensure a correlated measurement. Basically the vacuum state of the two space like separated locations are said to be ‘Superentangled’ (if I am reading it correctly).

I don't think that's an accurate description of what happens in such a measurement.

For concreteness, let's focus on an EPR setup (the measurements there don't depend on vacuum fluctuations, but they do depend on a state that's strongly entangled across a spacelike separation). Many people think that QM requires an instantaneous "action at a distance" to ensure the EPR measurements are correctly correlated. That's wrong, as I can demonstrate very easily (and have before on this forum, actually).

from the Conclusions

The local fields allow the possibility of arbitrary space-like distant effects from arbitrarily localized actions, equally counterintuitive and equally compatible with Lorentz covariance!

That's a pretty technical paper. The statement quoted above does not seem to follow from the math (which, if correct, shows that one can come arbitrarily close to some distant effect using the class of operators he considers, not that one can achieve it). I'm not sure what to make of the results in there; they don't have any clear interpretation in my view.

 

[The Man]

Well, if there's a standard meaning to "deterministic" in physics it's that the state of the system at time t>0 is completely determined by its state at t=0. QFT and QM in the MW interpretation are deterministic according to that.

Again simply an exemplification of the point you quoted and under the constraints of that potentially “standard meaning to "deterministic"” the universe is then “deterministic”. Since the state of a system in that universe at some time t>0 is completely determined by its state at t=0.

True, but it's very hard (perhaps impossible) to come up with theories that manage that. And it's unnecessary, since MW has no such non-locality and works perfectly well.

Indeed very hard, perhaps impossible (unfortunately not everything can be done by simply dividing measurements). Since MW has no such non-locality, works perfectly well as a QM interpretation and is deterministic according to the previously mentioned constraint, then so too is the universe.

I don't think that's an accurate description of what happens in such a measurement.

I didn’t really think that you would.

For concreteness, let's focus on an EPR setup (the measurements there don't depend on vacuum fluctuations, but they do depend on a state that's strongly entangled across a spacelike separation). Many people think that QM requires an instantaneous "action at a distance" to ensure the EPR measurements are correctly correlated. That's wrong, as I can demonstrate very easily (and have before on this forum, actually).

I have no doubt that many people do as I have no doubt that you have done as described in the latter.

That's a pretty technical paper. The statement quoted above does not seem to follow from the math (which, if correct, shows that one can come arbitrarily close to some distant effect using the class of operators he considers, not that one can achieve it). I'm not sure what to make of the results in there; they don't have any clear interpretation in my view.

Apparently so too in the view of the author as the conclusions are rather ambiguous (other then the comparative details) and simply argues for keeping both considerations open, much as I have been doing here. However, I did find it interesting and relevant to the discussion.

 

[INRM]

What about it?

What were the exact findings?

No.

Why no?

 

[Reality Check]

What were the exact findings?

Why no?

Afshar experiment

 

[Tumbleweed]

The magnitude of spin of an elementary particle is constant, it cannot be slowed down or sped up by any means, only its direction can change.

With entangled particles, you don't know the spin state of either particle until you do a measurement. The measurement of any one particle is random, but the correlation between them perfect: if you measure your half of the pair, you know what Bob's will be even if he hasn't measured it yet. But if you're on earth and he's on Mars, how do you send a message to Bob? You can measure the spin of your particle, and instantly Bob's particle's spin will have a correlated outcome, but you can't MAKE your spin have a particular outcome before measurement. So what does Bob observe? Nothing, unless he measures his spin, and when he measures his spin, it appears to be random until he talks to you, which happens at light speed. You can't send a super-luminal signal, because no result from Bob's measurement will tell him anything about what you did. He won't even be sure that you measured your particle at all until he talks to you.

What if your only goal was to get the particle on Mars to react instantaneously by measuring its twin on Earth, no Bob necessary. You dont care what the results of your measurement is, only that there is a reaction. Could that be used as a control circuit?

 

[Tumbleweed]

Nope.

I could be wrong about this, but I suspect you're thinking of the big bang in terms of a big empty universe except for a little bit of super-compacted matter which then explodes out into this previously empty space. But that's not what happened. Space itself has expanded. The distinction is important, and if you can wrap your head around it, the rest should fall into place easily.

The CMB doesn't actually originate from the initial bang, but from a time shortly after that when space had expanded enough to become transparent (initially it was full of hot dense plasma). When the universe became transparent, the CMB was let loose into the universe from everywhere, and in all directions. There is no edge to the universe (it's either infinite or it wraps around on itself), so there's nowhere for the CMB to escape, and everywhere we look, we're looking back in time within the universe so we'll always see the CMB..

So you are saying its kind of like one of those Klein bottles? And that when we look at early galaxy photons we are looking at photons that have "wrapped around"?

 

[Reality Check]

So you are saying its kind of like one of those Klein bottles? And that when we look at early galaxy photons we are looking at photons that have "wrapped around"?

He is saying that the universe does not have a boundary. It is either infinite or wraps around on itself, i.e. either like or not like a Klein bottle.
This is to do with the CMB not "early galaxy photons".
An analogy for the CMB could be to think about a small balloon filled with fireflies and imagine being at a point in the balloon. You can see the fireflies all around you. Now let the balloon expand. The fireflies are still around you.

When we look at "early galaxy photons" we are looking at photons from galaxies when the universe was young. They have traveled from the galaxies to us. In some cosmologies I think this includes the possibility of traveling along a "Klein bottle loop".