Science nerds of the Escapist: "hidden variables" or true randomness?

[renegade7]

Quantum physics kind of threw a monkey wrench into the philosophy of science. Before QM, classical scientists assumed that the universe was at its heart deterministic, that is, if every piece of information in the universe could be known then its state at any time in the future or past could be determined with perfect accuracy. Along comes quantum mechanics, and that all goes out the door.

The reason is that observing a system necessarily requires putting some energy into it. For instance, when you shine a flashlight on something to look at it you are essentially directing light energy at it. In our macroscopic classical world, this is rarely enough to have any great effect on the system. However, at the subatomic level, shining a photon on something is in many cases enough to completely upset the system you're looking at. For instance, if you tried finding the positions of the electrons by putting the atom in a magnetic field, you would perturb the atom and move the electrons. All you'd be able to do is get a picture of a fuzzy cloud of areas where the electron PROBABLY is, in theory, the actual particle itself could be anywhere in the universe although practically speaking it is of course far more likely to be in that region near the nucleus of the atom.

There are three camps that philosophers of science are divided into on this:

The first is that this is simply a matter of technology. The state of a quantum particle can be known with 100% certainty, once we have the right technology, and the universe is fundamentally deterministic right down to the quanta. "God does not play dice" basically.

The second is that the universe is on the fundamental level completely deterministic, and while the variables that would be needed to construct such a picture do exist, it's just in principle impossible for us to find them.

The third is probabilistic determinism. That is to say, the universe at the most basic level strictly contains an amount of pure randomness, and it is an unavoidable fact of reality that not only can the state of a particle not be known to 100% precision, but that state of the particle itself is not determined by a 100% precise process. At the macroscopic level enough of this randomness either cancels out or becomes negligible enough for us to not to generally be concerned with it (although it can be "amplified" so to speak into the macroscopic world, for instance with a true random number generator http://photonics.anu.edu.au/qoptics/Research/qrng.php), but the fact remains that in principle the universe by its very nature will always obscure some amount of information from us. Or "not only does God play dice, but he throws them in places where we can't see them".

The amount of randomness is up for debate: the universe could actually be more random than deterministic, or it could be more deterministic than random. Knowing this for sure would require the construction of a unified field theory connecting the quantum scale to the macro-scale, and many scientists, perhaps not without good reason, are skeptical that such a thing will ever be possible.

I'm curious if anyone else has ever encountered or thought about these issues.

My own thoughts

Spoiler

Being something of a pragmatist, I tend to take the third position. The uncertainty principle has been so soundly confirmed by the last 100 years of progress in physics that I am just deeply skeptical of the first position, and in regards to the second, then I pretty much have to go with the "invisible pink unicorn" argument: if it exists but I can't see it, interact with it, or detect it in any way, then for practical purposes it does not exist. As for how much is random vs how much is deterministic, I think I have to stay an agnostic on that until some kind of unified theory connecting the quantum to the macroscopic is developed.

 

[Zombie_Fish]

The first is that this is simply a matter of technology. The state of a quantum particle can be known with 100% certainty, once we have the right technology, and the universe is fundamentally deterministic right down to the quanta. "God does not play dice" basically.

This is just plain wrong. It's not a case of "We just don't have the technology", it is a case of "It has been proven Mathematically that we cannot distinguish with certainty two arbitrary quantum states". If we could then we would be able to violate the uncertainty principle, the no-cloning theorem and probably achieve superluminal communication while we were at it.

The second is that the universe is on the fundamental level completely deterministic, and while the variables that would be needed to construct such a picture do exist, it's just in principle impossible for us to find them.

If this is something like the 'Hidden variable model' then this was proven wrong by Bell's Theorem. His paper gave an example of a game which you had a greater chance of winning via the use of quantum mechanics than you did via the use of hidden variables alone.

By a case of elimination, I'm left agreeing the most with the third option. As for how much is random versus deterministic, I'd go with the camp that a unifying theory is probably impossible. Such a grand theory to me seems reminiscent of what Mathematicians tried to do in the 19th and 20th century, which was also proven impossible.

 

[Mezahmay]

I'm inclined to believe it is the first case. Not only does it sound proper to me, but in the light research I've done in the last hour or so I've learned it is theoretically possible to violate the uncertainty principle [http://phys.org/news/2013-02-spacetime-violate-heisenberg-uncertainty-principle.html] using a circuit with an open timelike curve. Admittedly I am not well versed in this subject or subjects like it since I'm a chemical engineering major and don't follow physics news closely, but there have been a lot of instances in human history where technology was the limiting factor for further understanding. As I understand the case with overcoming problems like measuring units smaller than the Planck length, the limiting factor is the energy required to produce waves with short enough wavelengths that are relevant on a quantum mechanics scale. I have confidence that some day that barriers and barriers like it can be overcome with time.

EDIT: Tangent thought, I feel "science nerd" is a little too vague. Science encompasses many things and not many people are that into quantum physics. I suppose this is more of a philosophy of physics question though... Damn. I'm now conflicted.

 

[Wyes]

The reason is that observing a system necessarily requires putting some energy into it. For instance, when you shine a flashlight on something to look at it you are essentially directing light energy at it.

I just wanted to point out that while this is true, it isn't the whole picture. You can do interaction-free measurements and you still mess with the system. This is because the method of measurement isn't what matters, it's the fundamental act of measurement itself (which is even weirder).

Because of that, I've always been inclined to think of it as the third option. Which is good, because next year I'll start my first step into the world of quantum optics research.

 

[renegade7]

I'm inclined to believe it is the first case. Not only does it sound proper to me, but in the light research I've done in the last hour or so I've learned it is theoretically possible to violate the uncertainty principle [http://phys.org/news/2013-02-spacetime-violate-heisenberg-uncertainty-principle.html] using a circuit with an open timelike curve. Admittedly I am not well versed in this subject or subjects like it since I'm a chemical engineering major and don't follow physics news closely, but there have been a lot of instances in human history where technology was the limiting factor for further understanding. As I understand the case with overcoming problems like measuring units smaller than the Planck length, the limiting factor is the energy required to produce waves with short enough wavelengths that are relevant on a quantum mechanics scale. I have confidence that some day that barriers and barriers like it can be overcome with time.

EDIT: Tangent thought, I feel "science nerd" is a little too vague. Science encompasses many things and not many people are that into quantum physics. I suppose this is more of a philosophy of physics question though... Damn. I'm now conflicted.

They do not mean "circuit" in the electronic sense, but rather the loop that forms in a world line (the path of an object through 4-D spacetime) in a "closed" timelike curve wherein an object returns to not only its position in space but also its position in time (ie it goes forwards into the future and then returns to the point both in space and time before it did anything). An "open" timelike curve is one in which the object does not return to its worldline at the point which it departed, but at another location in space and another moment in time entirely. Or rather, it violates causality.

This discovery isn't of a violation of Heisenberg's uncertainty principle, but rather just a new way to look at it in theoretical applications. What they do is essentially break the causal structure connecting the particle to different points in space and time. Basically, if you can travel through time while conserving energy, mass, and information perfectly (which is not possible), you are able to violate the uncertainty principle as long as that particle does not interact with anything while doing so.

That last part is the catch. If the particle in question is the only particle and force-carrying object in the universe, then it could violate uncertainty by being in a position to ignore superposition.

So, we've got two really huge ifs here. IF the particle is able to travel backwards and forwards in time in a non-trivial way (theoretically possible but not known to physically occur) and IF it is able to do so while not interacting with anything (definitely impossible in the current understanding of physics) then it is able to violate uncertainty. And, even though you WOULD in theory be able to get a perfectly precise view of the particle's state, you still would not be able to predict its next state with perfect certainty. Not to diminish the paper, because it actually is pretty interesting and a possibly useful discovery, but to just clarify what it means.

The reason is that observing a system necessarily requires putting some energy into it. For instance, when you shine a flashlight on something to look at it you are essentially directing light energy at it.

I just wanted to point out that while this is true, it isn't the whole picture. You can do interaction-free measurements and you still mess with the system. This is because the method of measurement isn't what matters, it's the fundamental act of measurement itself (which is even weirder).

I know, but I didn't want to start getting into all of the weirdness of conservation of information independent from mass and energy and thought it would be easiest to read to just go with the "intro to modern physics" explanation.

Because of that, I've always been inclined to think of it as the third option. Which is good, because next year I'll start my first step into the world of quantum optics research.

Nice. I haven't taken my qualifying exams yet (shudder) but I'm thinking of going for solid state or maybe engineering physics. Best of luck.

 

[Mezahmay]

They do not mean "circuit" in the electronic sense, but rather the loop that forms in a world line (the path of an object through 4-D spacetime) in a "closed" timelike curve wherein an object returns to not only its position in space but also its position in time (ie it goes forwards into the future and then returns to the point both in space and time before it did anything). An "open" timelike curve is one in which the object does not return to its worldline at the point which it departed, but at another location in space and another moment in time entirely. Or rather, it violates causality.

This discovery isn't of a violation of Heisenberg's uncertainty principle, but rather just a new way to look at it in theoretical applications. What they do is essentially break the causal structure connecting the particle to different points in space and time. Basically, if you can travel through time while conserving energy, mass, and information perfectly (which is not possible), you are able to violate the uncertainty principle as long as that particle does not interact with anything while doing so.

That last part is the catch. If the particle in question is the only particle and force-carrying object in the universe, then it could violate uncertainty by being in a position to ignore superposition.

So, we've got two really huge ifs here. IF the particle is able to travel backwards and forwards in time in a non-trivial way (theoretically possible but not known to physically occur) and IF it is able to do so while not interacting with anything (definitely impossible in the current understanding of physics) then it is able to violate uncertainty. And, even though you WOULD in theory be able to get a perfectly precise view of the particle's state, you still would not be able to predict its next state with perfect certainty. Not to diminish the paper, because it actually is pretty interesting and a possibly useful discovery, but to just clarify what it means.

You're right about the circuit thing. That was poor phrasing on my part. I will try to avoid such an error in future discussion I may have on physics. And thank you for clarifying some of the points made on that paper. Admittedly I did not understand its full extent and this has helped form a more complete sense of its content and practical limits. I even got to learn what superposition means on a quantum mechanics level! So much learning today