Ah, July, when a young man’s fancy turns to… thermodynamics. Seriously, it is just broiling up here on the second floor. My plan tonight was to post the final “Category IV Bad Movie” entry, but that’s going to be a long one, and it’s just way too hot to even try that tonight.
Instead, I’ll riff off a post by physicist Chad Orzel, who discusses how “common sense” can apply to physics. Orzel makes a distinction between one kind of common sense, our natural human intuition about how the universe works, and the second kind of common sense, the logic of the scientific process. I’ll focus on the first kind, though.
Most people who have taken physics classes at some point in their lives will tell you that quantum mechanics (or alternatively, special relativity) is weird and counter-intuitive. And these people are absolutely right about when they say this. However, whenever I hear this complaint/observation, I think of two counterpoints.
First, our minds evolved in a world that operates at a particular scale and energy. Here’s what would be really weird: if we were born with an intuitive understanding of the physics of extremely hot things or extremely large things or extremely small things. Why would evolution have provided us with that functionality? And why would we think that our realm of “tables and chairs” would be anything like the realm of galaxies or particles?
Second, all realms of physics are weird, even boring old Newtonian mechanics. All objects instantaneously exert an invisible attractive force on each other? Really? How? Who’s crazy enough to believe that? (Certainly not physicists.) And for that matter, even if you ignore all the conceptual and philosophical issues, it’s still hard to work out Newtonian problems. Aristotlean physics might be commonsensical, but Newtonian physics clashes with common sense all the time.[1] There are all sorts of fun Newtonian thought-experiments out there that not only trip up all “regular people”, but also most physics undergrads, many grad students, and even the occasional young and unwary professor. For examples of what I mean, go read Lewis Epstein’s outstanding Thinking Physics. If you think you know Newtonian mechanics, this book will blow your mind. Ditto for fluid mechanics, electromagnetism, and other less sexy realms of physics.
Hmmm. I really sold that one, didn’t I?
1. I remember that as a little kid, my science fair project one year was to prove that objects of equal mass fall at the same rate. Despite what Galileo had to say about the matter, I was sure that the heavier rocks were hitting the ground first. Dropping rocks off a 6′ step ladder was insufficient; we had to go to the park and drop the rocks off a 20′ climbing structure before I was convinced. This experiment would be impossible to reproduce today, since such climbing structures have long been litigated out of existence.
I should lend you my copy of How to Build a Time Machine.
If I built a time machine, I’d use it to go back in time three weeks and buy a mini air conditioner.
Hey, at least you have a swimming pool.
I always look at it like this: How do we know that we AREN’T born with an innate understanding of such things, and that common education and social conditioning ruins our minds for such things?
What if you brought up a child teaching him these things as “normal”, what would his world look like?
Actually, you can tell which children are raised to have an innate understanding of quantum mechanics — they’re the ones that are always pedaling their tricycles into walls at full speed, hoping to tunnel through to the other side.
On a side note, did you know that the dark-adapted human eye can actually register individual photons? The photon is the only particle that we can directly percieve with our own senses. Pretty cool, eh?
I don’t know about you, but I can certainly perceive the vibration of individual air molecules. Of course, that means I had been drinking the night before and failed to hydrate myself properly.
Heh. Well, it turns out that the “one photon” thing is a bit of old physics folklore — the truth is that we can detect a few tens of photons. Still pretty impressive, though!
Mammal eyes need on the order of 10 photons. Frog eyes, however, are capable of generating an electrical pulse from a single photon. (Or so I’ve been told.) This makes for a very interesting Schroedinger’s Cat experiment. A single photon behaves as a probability field/wave, but should, in theory, generate different configurations in the brain of the frog, depending on what it does. This sort of situation is what led Roger Penrose to suggest that perhaps state collapse is triggered by the potential arrangements of matter implied by a set of probabilities, to diverge from their average or center-of-mass by an amount requiring the emission of a graviton in order to maintain the proper curvature of spacetime. In that case, it’s not observation that collapses states; it’s the fact that the instrument or mind doing the observing has a physical analog that has too much mass to maintain both states.
Possibly a crackpot theory, but kind of interesting, nonetheless.
I didn’t quite follow the crackpot theory… but I just think it’s sad to think that frogs have a closer connection to the quantum world than we do.
The theory is intended to roll gravity up with the rest of quantum electrodynamics.
The basic Schroedinger’s Cat thing says that, if there’s a 50/50 chance that a particle has decayed, and if it’s decayed the cat is dead, then there’s a 50/50 chance that the cat is dead.
But if the cat is dead, the mass of it’s body will be arranged quite differently from if it’s alive, right? And spacetime curves depending on the arrangement of mass in it. (General Relativity, and all that.) The graviton is supposed to be the quantum particle that is emitted to “re-curve” spacetime when mass moves around (or is exchanged with a non-mass form in nuclear reactions). Penrose says that gravitons are emitted from state-collapse events, when the arrangements of mass (and hence of spacetime curvature) implied by the possible states diverge by a certain amount — the smallest quantum of gravity.
You follow?
I completely follow your comment #10, but I’m not totally sure I understand comment #8. So is Penrose saying that IF the possible states differ by at least one graviton, THEN you get a state collapse?
He’s making a stronger “if and only if” claim. But yes, that’s the idea.
Ah, okay. Maybe I’m not understanding the importance of what he’s getting at?
Let’s say our object of interest (the cat, a radioactive nucleus, whatever) undergoes a state collapse and emits one or more gravitons. If I detect the gravitons, then okay, great, the state has collapsed. The cat is definitely Dead. Or Alive. But If I’m shielded from the gravitons, then from my perspective, the object of interest is still in a superposition of states. We are still faced with the old “problem” of observation, we’re really right back where we started.
As a corollary, we can always construct a thought-experiment where we can’t possibly detect the state change when it emits those gravitons, but we can detect the state change through other means. So I don’t see how gravitons would be more fundamentally related to state collapse than anything else.
I’m not sure I completely understand it either, but I think the main point was to drive a stake through the heart of the “spooky” idea that observation causes state collapse. Clearly there are plenty of macro events that have a definite outcome, even if you’re uncertain what it is. For example, if I draw a card from a pack and don’t show it to you, even before anyone has observed the card, we can be certain that has some identity — it is not a superposition of 1/52 probability for each card.
Penrose is saying that quantum stuff is the same — it’s not that observation causes states to collapse, it’s just that observation requires a scale too large to maintain superposition.