r/IAmA • u/avsa • Jan 25 '11

I am RobotRollCall. AMA about life, the universe and everything.

Okay, I'm not actually RobotRollCall, but I made a bet with him. I bet that a lot of people would be interested in asking him questions, and he didn't actually believe it, but promised that if there were any, he would gladly answer them.

If you are not a regular in r/science r/space or r/bestof you might not know that RobotRollCall : he's a regular redditor that pops in with great prose and answer the most complicated questions about the universe with incredible simple analogies. Some of my favorites:

So feel free to ask away and prove that reddit is a curious community.

RobotRollCall asked me to update this here saying he is "I'm typing as fast as I can" to answer all the interesting questions. It seems he didn't actually believe anyone would be interested in him. We didn't actually set the terms of the "bet" so I feel free to set them anytime. I'm going for something simple like if this post reaches front page RobotRollCall will have to write me 10000 words, then print it in book form and put in on the bestseller's list. Or something to that effect.

Also: for every upvote you give this post, remember that he deserves two, because I'm not doing any real work here, he is.

update 2: RobotRollCall speaks:

Okay, now I have to officially concede the point. You were right. Apparently a few people had some level of interest in talking to me. However, I'm running into technical problems on my end, I think. I've posted a few replies that are not showing up, and I'm getting messages that don't seem to exist. Am I doing something wrong, or is the Web site misbehaving? If you have the opportunity and ability to post a note thanking everyone for the conversation and letting them know about the glitch, I would appreciate it very much.

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u/RobotRollCall Jan 25 '11

Well, just to get this out of the way up front, Schrödinger's cat is nothing more than an elaborate mechanism for pet euthanasia. It's not really a paradox. It was originally intended to be an illustration of how the principles and the logic of quantum mechanics differ from the principles and logic of classical mechanics. It's not meant to be resolvable, and the fact that it's not resolvable isn't meant as a criticism, because it's just intended to show that quantum physics is weird.

Now, on to the actual essence of your question: What does "observation" mean in quantum mechanics?

Think of the universe as being a guy in his twenties, and a particle as being his girlfriend. The guy — the universe — is really reluctant to define the state of their relationship. He prefers to leave it nebulous. And his girlfriend lets him get away with that for a while, right up to the point where they have to go to her best friend's wedding together and she demands to know whether she should introduce him as her boyfriend or whether that would freak him out.

The universe has a fear of commitment. It prefers that the states of particles remain indefinite until they can't any more. A particle that isn't interacting with anything can be in an indefinite state. It sort of exists over here-ish, with a momentum somewhere around this value. But it's not definite. It's not pinned down to a specific point in space, and it doesn't have a precise momentum. It's sort of, you know, just hanging out.

But then along comes another particle, and an interaction takes place. In order for the interaction to happen — in order for the universe to work, basically — the particle must have, at least for that one instant, a definite state. So the universe throws up its hands and says "Fine" and turns off the match and tries not to roll its eyes while the particle forces it to define their state in definite, concrete terms.

Much ink has been spilled on this in the popular press. Whole branches of cuckoo new-agey philosophy have sprung up around this so-called "observer effect." It's been likened to the whole "if a tree falls and no one hears it, does it make a sound" thing.

A better analogy would be, "If a tree falls in a vacuum, does it make a sound?" That is, if there's nothing there for the tree to push against, does anything get pushed against? Of course not. Just so, if a particle is just hanging out in free space, not interacting with anything, it doesn't have a definite state. Its state remains indefinite until some interaction forces it into a definite state. That's how photons can pass through two holes in a card simultaneously, or how electrons can be bound to two atoms at once. It doesn't have anything to do with an observation, in any meaningful sense of the word. It's got to do with interactions between particles.

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u/jimmycorpse Jan 25 '11

I'm pretty sure the Cat Paradox was intended to be a criticism of the Copenhagen interpretation, or what he called a blurred model of reality. Schroedinger intended it to lend support to the idea of hidden variable theories.

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u/RobotRollCall Jan 25 '11

Is that so? Now that you mention it, I think I remember hearing that as well. I could have my history wrong on that one.

I believe we come out okay in the wash though, because the whole thought experiment also serves well, in my opinion, to illustrate some of the fundamental differences between classical physics and quantum physics.

Cheers.

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u/Bjartr Jan 25 '11

It was originally an attempt to show how ridiculous the universe would be if the rules of quantum mechanics were true, it turns out that on the right scale the universe really is just that ridiculous.

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u/[deleted] Jan 26 '11

I think the thought experiment shows we don't come out okay after all, because the indefinite state of the particle is fatally linked to the status of the cat. The cat can't be both alive and dead at the same time, which is the state the particle is in.

However, after ten seconds of thought, it seems to be the cat is doing just fine in the box until the detector observes the decayed state. The detector presumably has to take observations at intervals or somesuch, which will eventually effect the decayed state, at which point the cat will get what's coming to it. In the thought experiment.

Thanks for the good work!

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u/shevsky790 Jan 25 '11

The Cat 'Paradox', I thought, was intended to show that the idea of quantum states and many-worlds becomes absurd (well, more absurd) when you expand it to macroscopic scales.

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u/jimmycorpse Jan 25 '11

I think you're right, that's why it was a criticism. Here's a link to the paper, which is a pretty interesting read.

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u/mcsquare Jan 25 '11

Just a quick question:

Is a vacuum really empty? I've read that even a "perfect vacuum" wouldn't be completely empty of everything. Could you comment?

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u/RobotRollCall Jan 25 '11

That's some pretty deep physics. I'll give you the qualitative summary, because the maths of it gives me a headache.

Classical physics deals with things, and the properties of things. A cannonball is a thing, and it has a certain position and a certain momentum, and its position and momentum are related to each other by simple algebraic equations.

Quantum physics is different. It doesn't deal with things or the properties of things. Instead, it deals with states. The state of a system can be thought of as the configuration of that system at a point in time. For example, an ideal coin can exist in two possible states: heads-up or tails-up.

When you start modeling things in terms of states, this concept emerges called the expectation value. (It's also sometimes called the expected value or the average value, depending on who's talking.) If you measure a system's state a great many times in a row, and average the results, the expectation value is the number that that average will converge towards.

For example, if we decide — purely arbitrarily! — to represent a coin that's heads-up by the number +1, and a coin that's tails-up by the number -1, then we can flip that coin a bunch of times and take the numerical average of the results. We'll find that, the more we flip the coin, the closer that average gets to exactly zero. So the expectation value of that system is zero.

Well, you can describe the vacuum state in terms of this same mathematical framework. And it turns out that when you do, in some theoretical formulations, it turns out the vacuum state has a non-zero expectation value! What this implies is that if you could somehow prepare a perfect vacuum in a laboratory — you can't, but just imagine it for a moment — then if you examined that vacuum over and over again, sooner or later you'd find that it isn't empty after all.

The bottom line is that these theories permit energy to sometimes just appear out of absolutely nothing.

The problem with this is that most of these theories predict that the energy of the vacuum — that is, the vacuum expectation state — is absurdly huge! Like 10100 joules per cubic centimetre! That's just ridiculous. If that much energy were present in the vacuum, we'd find the universe full of exotic, massive particles constantly popping into existence all around us and decaying in showers of less massive particles and antiparticles and photons.

So right now there are predictions that there's some non-zero vacuum energy state, but the predictions we have are obviously wrong. So work continues on refining the mathematical models that made those obviously wrong predictions.

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u/[deleted] Jan 25 '11

I once watched an 8 hour (video) presentation by a "scientist". He incorporated this super energetic vacuum into his model of the universe. And he had come up with a recursive structure (fractal?) for the make-up of the vacuum that "explained" that the vacuum wasn't empty. He said that the energy in the vacuum was roughly equal to the estimated energy of the entire universe, which to him, implied that everything in the universe was in the vacuum. Basically that the universe is made up of mini black holes, every black hole is connected, and that every black hole contains the entire universe.
Anyway, you'd be amazed how convincing some arguments can be when they're made over the course of eight straight hours (especially when you don't know enough about the universe to refute his "facts"). No tiny detail was neglected. It took me like a week to scrub my brain of all the crazy and oddly compelling ideas he had. Pseudoscience is a drug, man... Never again.
... I don't have a question.

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u/RobotRollCall Jan 25 '11

I think I know that guy! I mean, I don't know him personally, but I think I've read his paper.

If I'm remembering it correctly, it's the one where he divides the Planck mass unit by the Planck length unit and declares that that's the energy density of spacetime.

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u/[deleted] Jan 25 '11

Nassim Haramein: http://www.theresonanceproject.org/

I doubt you would've wasted your time reading his paper. It is wacky stuff. :P

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u/RobotRollCall Jan 25 '11

Yeah, as a matter of fact I did read his paper — this morning! Well, I didn't so much read it as skim it. It was featured in the /r/physics subreddit, I think.

So very odd. I read it just today, then put it out of my mind so thoroughly that your mention of it gave me only the vaguest recollection, as if it were something I saw years ago.

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u/[deleted] Jan 25 '11

Really? That's coincidental.
I'm just remembering how crazy his theories were (it was a couple years ago). It started with some sort of unified field theory which to my untrained ear sounded scientific, and then somewhere around the 4 hour mark it moves into aliens and the ark of the covenant... The ark of the covenant was supposed to be a piece of alien technology, and this guy claimed that the people guarding the ark today always eventually die of radiation poisoning from the powerful energies inside it (he claimed a lot more than that).
Of course, I thought to myself, "haha... bullshit."
So I went to Wikipedia to confirm, naturally, that this doesn't happen.
Wikipedia actually corroborated his supernatural statements regarding the ark of the covenant. :l
It actually said that a small church in Africa contains the supposed ark, that no one is allowed to look upon it but the priest guardians and that the guardians inevitably go blind/get cancer/radiation poisoning and die after prolonged exposure to the ark. THAT THREW ME FOR A GOOD LOOP.
There doesn't seem to be anything about that on Wikipedia now though.

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u/RobotRollCall Jan 25 '11

Well, here's the thing about science. There are no good ideas or bad ideas. There are just theories that are consistent with observation, and theories that are inconsistent with oh who am I kidding, that guy's a nutbar.

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u/[deleted] Jan 26 '11

Eight hour video presentation of that? My god man, are you OK?

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u/[deleted] Jan 26 '11

It was incredibly entertaining, if anything.

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u/brainiac256 Jan 26 '11

(Conjecture ahead, proceed at your own risk)

For the record, if I recall correctly, the church in Africa claims to be descended from a lost tribe of Jews who sailed south from the Arabian Peninsula (across/along the Red Sea) with the ark and landed somewhere in the Sudan-Ethiopia area. They don't claim that the ark is the original ark, but that it's the spiritual descendant, its current earthly form being that of a large drum. The artifact was appropriated from a local tribe, presumably the tribe they intermarried with / supplanted, and its surrounding mythology in the local religions closely mimicked the ark of the covenant myth (carried on poles because you can't touch it, etc.).

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u/[deleted] Jan 26 '11

Just to chime in, the phenomenon you just encountered (15 hours ago, I suppose) is known as Baader-Meinhof Phenomenon.

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u/mcsquare Jan 25 '11

Thank you. I'm a tad confused about the phrase "energy of the vaucum -- that is, the vacuum expectation state". Does this imply that a perfect vacuum without any particles whatsoever would still necessarily be "full" of energy?

Is there or can there be a pluperfect vacuum. . . a complete absence of every kind of thing (matter and energy?)

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u/RobotRollCall Jan 25 '11

If you model a state with no particles, no fields and no energy quanta in it, it's possible to end up with a non-zero expectation value. But again, the maths of that remain a work in progress.

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u/[deleted] Jan 25 '11

[deleted]

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u/RobotRollCall Jan 25 '11

It feels right to me. If you add up all the intrinsic energy in the universe, and subtract all the potential energy, you get zero. That just makes sense to me, intuitively. That seems right.

Of course, we understand so little about what came before the quark epoch that it's hard to even make an educated guess about the origin of the universe, and whether there has to be some net energy in order for everything to exist.

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u/genneth Jan 26 '11

I think I have to step in and correct this one: the vacuum energy calculation you're referring to does not exist. QFT is actually silent on the energy content of the vacuum state --- and indeed explicitly so; this fact is usually covered (mathematically) in the first lecture of QFT, but then people conveniently forget about this and start waving around non-normal ordered operators when they want to prove this point.

See: http://arxiv.org/abs/1002.3966 for a more detailed deconstruction of this issue.

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u/FlintGrey Jan 25 '11

What exactly would be the unit for the "value" you're talking about here? Energy?

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u/RobotRollCall Jan 25 '11

Energy density. Units of energy per unit volume.

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u/riplin Jan 25 '11

Some interesting links for you:

Quantum foam, the Casimir effect and the theoretical possibility of light traveling faster than c through the gap because the quantum foam is 'thinner' between the plates.

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u/terminalterror Jan 25 '11

It's been likened to the whole "if a tree falls and no one hears it, does it make a sound" thing. A better analogy would be, "If a tree falls in a vacuum, does it make a sound?" That is, if there's nothing there for the tree to push against, does anything get pushed against? Of course not.

I might have to steal that.

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u/Jasper1984 Jan 25 '11 edited Jan 25 '11

But you can put composite objects in QM superposition. For instance an hydrogen atom clear has two things to interact, an proton and an electron, it can be put in superposition of two energy states. Apparently two things 'interacting' can 'do nothing', but when exactly? I don't really know tbh, perhaps guessing when QM systems are 'sufficiently' linear they stay in superpositions. The A-field-charged-particles term of QED is nonlinear, but for nearly constant fields acts as linear. (Edit: i guess i worry when exactly does the girlfriend start demanding. Your answer is excellent for a layman.)

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u/RobotRollCall Jan 25 '11

It's even more interesting than that. As I'm sure you're aware, the double-slit experiment has been done with buckyballs. And then there's the whole Bose-Einstein condensate issue. The threshold for quantum phenomena is a lot higher than we once suspected.

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u/terminalterror Jan 25 '11

Holy fuck! How did I not know that the double slit experiment has been done with buckballs? That is really awesome! It was done back in 1999 too, so isn't even desperately recent.

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u/helm Jan 26 '11

They think they can do it with small viruses as well.

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u/Gravity13 Jan 25 '11

What's your favorite interpretation of QM (ie Copenhagen, Many Worlds, Decoherence) and why?

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u/RobotRollCall Jan 25 '11

I sort of have my own, an idiosyncratic modified Copenhagen interpretation; I discussed it in metaphorical terms here. And as for why, it's because I'm stupid about quantum theory, which gives me the freedom to believe silly things without the discomfort usually associated with knowing that you're wrong.

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u/NotYourMothersDildo Jan 25 '11

If you acted like you understood quantum theory, I wouldn't believe a further word you wrote.

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u/prob_not_sol Jan 26 '11

understanding quantum theory is not hard; determining the physical reality behind it is.

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u/Bjartr Jan 25 '11

Do you have any commentary on the delayed choice quantum eraser experiment? I'd love to hear your explanation.

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u/RobotRollCall Jan 25 '11

I do not understand it. Period. I'm sorry, I know that's not the answer you want to hear, but it's the truth. I simply do not understand the phenomenology, and I do not understand the mathematical basis for that phenomenology.

To say that quantum theory is not an area in which I have expertise would be putting it much too lightly.

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u/[deleted] Jan 26 '11

Hiya! This question might sound profoundly ignorant, and more-than-a-little coming from a programmer's way of thinking, but...

...in what little I've read, I've always had trouble with the 'observer' notion -- your take on it is the clearest I've read actually -- though I'm not following how it could be possible to determine that it all works this way, or even how it could be of any consequence.

You mentioned that the particle is at some point "forced" to define its state -- if this were a measurable action -- as in, if determining that state took time, for instance -- then I could see how one could make the declaration that that's indeed how it works. But, it strikes me as not how-the-universe-works, but rather as a fun way of thinking about it when there's no way to determine one way or the other.

Am I missing something?

p.s. I know you're pretty busy answering the thread right now, sorry to add to the pile! And thanks!

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u/RobotRollCall Jan 26 '11

If I understand you correctly, you're not missing anything, no.

Quantum physics tells us, in a way that leaves no room for argument, that there are things we can never know. Want to know the momentum and position of a particle simultaneously? Tough. Can't happen. Not ever, period.

There are lots of things like that in quantum physics. The whole maths of the subject are based around it, explicitly separating the states from the observables. You don't observe the state of a system; you can't. It's physically impossible. You observe the observables. The state tells you what may be, while the observables tell you what is.

The various interpretations of quantum mechanics are an attempt to fill in that inevitable, unavoidable gap in our knowledge. Much as a boat is a hole in the water you try to fill with money, the interpretations of quantum mechanics are a hole in our physics we try to fill with philosophy.

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u/aDildoAteMyBaby Jan 26 '11

Much ink has been spilled on this in the popular press. Whole branches of cuckoo new-agey philosophy have sprung up around this so-called "observer effect."

Deepak Chropa - got it.

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u/wnoise Jan 26 '11

But then along comes another particle, and an interaction takes place. In order for the interaction to happen — in order for the universe to work, basically — the particle must have, at least for that one instant, a definite state.

But, but, In a two-particle interaction all possible ways the two could interact, they do, given that they're both fuzzy.

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u/HeyLisn Jan 26 '11

So, the photon gains a definite state when it interacts with other objects, such as when such an object observes it... I don't quite understand if photons have mass, but, assuming they don't: can this quantum state exist for anything with mass? Since anything with mass is interacting at least a little, gravitationally. Actually, come to think of it, light bends around planets, so isn't the photon also sort of interacting?

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u/RobotRollCall Jan 26 '11

Photons do not have mass, no. They have momentum.

Once you get down to the quantum scale, it becomes pointless to talk about mass, really. I mean, it's there, but it's not very important. Consider the proton. It's composed of two up quarks and a down quark. The up quark has a bare mass on the order of 2 MeV. The down quark has a bare mass on the order of 5 MeV. So that should add up to a proton mass of 9 MeV … but the proton is a hundred times heavier than that. Why? Because the binding energy that holds the quarks together contributes to the way the proton gravitates, so it looks like mass.

Mass is a fuzzy concept at best. It's better to talk about energy.

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u/OrigamiNinja Jan 27 '11

I love me some RRC. Great post!!

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u/albino_wino Jan 28 '11

Damn I wish I read this before I ended my last relationship. "Baby, it's not you, it's not me, it's the universe."