Quantum Wildlife

David Wallace wrote an article about reductionism, emergence, and worlds in the many worlds interpretation of quantum mechanics that’s enlightening and more accessible than his earlier writings:

Decoherence and Ontology (or: How I learned to stop worrying and love FAPP)

Ultimately, though, that a theory of the world is “unintuitive” is no argument
against it, provided it can be cleanly described in mathematical language. Our
intuitions about what is “reasonable” or “imaginable” were designed to aid our
ancestors on the savannahs of Africa, and the Universe is not obliged to conform
to them.

I especially enjoyed figure 2 and footnote 14.

Wallace also has a latest update on the program to derive Born probabilities from decision theory:

A formal proof of the Born rule from decision-theoretic assumptions

I tend to think of Wallace’s as the most orthodox interpretation of quantum mechanics, it’s just that people don’t know it yet.

Three Bizarre Cosmology Disasters

Some say the world will end in fire, some say in ice. I say boooringggg. Here are some grand scenarios of cosmic fail that have not been given as much press as the big crunch and big freeze.

1. Spontaneous Decompactification

String theorists believe the universe has several dimensions that, unlike the ones we know, loop back on themselves in tiny “compactified” shapes. It has been suggested that this situation may not be stable in the long run, and that in billions of years random fluctuations could cause the universe to “spontaneously decompactify”. That means these other dimensions blow up to a macroscopic scale — a bubble expands at the speed of light, and then suddenly your surroundings are roomier than ever, in directions you never heard of. Unfortunately, I doubt the process preserves the structure supporting your brain and body or superintelligent yogurt or whatever you’ll care about then.

and this is what it looks like, not

2. Transition To a Supersymmetric State

Another speculation in string theory goes that the universe could randomly change from its current state, where supersymmetry is broken, to a different state, where supersymmetry is exact. Again, these things happen billions of years from now, if ever; else they’d have happened already. (What is supersymmetry? I don’t know, but I do know that even if I did know I still couldn’t tell you.) In such a universe, nuclear physics has to be redone from the ground up, and new kinds of matter replace our familiar ones; Louis Clavelli writes that “the physics of bulk supersymmetric matter is very much terra incognita”, and also that “a priori, it cannot be ruled out that Susyria is a new Galapagos teeming with abundant life”. Perhaps most intriguingly, he doesn’t rule out the possibility of supersymmetric bubbles coexisting and communicating with our normal world, although no life could survive the radiation blast at the transition event itself.

3. Naked Singularities

In general relativity, a singularity is a point or region in spacetime where there actually isn’t a point or region in spacetime because stuff blows up (this is not the technical definition that physicists use). A naked singularity is one that doesn’t have an event horizon causally separating it from the rest of the world. The so-called “Cosmic Censorship Hypothesis” says physical law prevents these from being created when big round things collapse under their own gravity; it is, however, unproven. According to Chris Hillman, it’s possible that such a naked singularity would set off a “thunderbolt” hole in spacetime expanding at light speed, leaving those in the vicinity without so much as a faint “om nom nom” to announce their instant death. Or to be exact, in Hillman’s words:

they are spindled and crushed by tidal forces which increase without bound in finite proper time.

Colliding gravitational waves and something called a “Wave of Death” supposedly could create the same result. Hillman dwells a bit on mad science applications, and it turns out that in the end there is also room for bright and happy optimism:

how can humans protect themselves against possibly inimical extra-terrestial
civilizations which might be -arbitrarily- more technologically advanced
than we are?  The all-too-familiar logic of the Cold War suggests that the
only possible defense is to develop a way of generating a Wave of Death.
Then, if a powerful extra-terrestial threatens us, we can threaten back by
warning them that we will destroy the Universe if they try to destroy us.

What Relativity Doesn’t Teach Us

In this pdf article John D. Norton investigates a long list of philosophical morals that have been drawn from relativity theory and finds most of them wanting — not true, not new, or based on either something more or something less than general relativity.

That could mean relativity isn’t as weird (to us) as we thought, or it could mean the old physics was weirder than we thought. Probably a bit of both.

Contrary to a recent commenter on Overcoming Bias (I forget who, maybe Eliezer), I think philosophers of physics tend to do better philosophy of physics than physicists, for an unmysterious reason: it’s their specialty.

Probability Backflow

Apparently in quantum mechanics you can set things up so that when you measure a particle’s velocity, you always find it going right, but the probability that on measuring its position you find it to the right of some fixed reference point goes down over time.

Quantum computing, quantum teleportation, quantum immortality, quantum suicide, quantum consciousness, quantum psychology, quantum golf… and now the quantum moonwalk?!

Relativity: Tool of the Phallocrat Reductocaust

Sometimes people talk about how modern physics shattered the old mechanistic, deterministic, reductionistic, observer-independent world view of pre-20th-century scientists like Newton and Laplace. This is rubbish. I’ll tackle the relativity case first, as it’s less controversial than quantum mechanics.

The reason it’s called “relativity” is that space and time are relative to a reference frame. In different reference frames, lengths and durations are different. For events separated far in space, different observers will disagree on which happened first.

Not supposed to be helpful, just thought there should be a picture.

But relativity theory is set up so that any disagreement between observers on time and space makes no difference to the causal ordering of what happens. Underlying it all is a perfectly un-relative thing called spacetime. A reference frame is nothing but a coordinate system; a different way of labeling the same structure. That different coordinate systems disagree on what happens first is no more philosophically meaningful than that people standing on different sides disagree on whether the house is to the left of the tree or to the right of the tree.

To talk about “observers” at all is misleading. There is no reason why I (as a cognitive system) have to use the coordinates in which I (as a block of matter) am at rest.

So although relativity theory forces us to rethink our concepts, it does not prove anything hippy or postmodern. It does not break with the program of representing the world as something mathematically precise, objective, and predictable. It is a continuation of that program by other math.

(possibly next up: quantum mechanics, chaos theory)

Time Slowing Down?

There’s a new theory that says time is slowing down and will end up stopping altogether, according to this newspaper article. Although the problem is of course in the translation from math to English and not in the theory itself, the idea of “time slowing down” doesn’t mean anything clear.

In a world like ours, processes happen in predictable proportions. Microwave radiation from cesium atoms completes a period about 3*10^17 times for every time the Earth goes around the sun. It’s necessary in practice to think of all these processes as depending on the same parameter called “time”. When we say the “rate of time” speeds up or “time goes faster”, we mean all processes speed up by the same factor. But time can’t go faster with respect to itself. Every second, one second passes. So it has to mean all processes speed up with respect to some other thing we also call “time”.

In everyday life when people say “time stood still” they mean an unusually large number of psychological events happened per physical event, causing (physical) time to slow down in (psychological) time. In special relativity every reference frame has its own time coordinate, and in every system events happen at a normal rate in the time coordinate corresponding to the reference frame in which the system is at rest; but events happen at a lower than normal rate in every time coordinate corresponding to a reference frame in which the system is moving. So here the other-thing-also-called-time is a different coordinate for the same thing.

But the newspaper article doesn’t say what their other-thing-also-called-time is. So all we can tell is that according to the theory, fewer things of one kind are happening compared to things of some other kind.

Mirror Matter

It’s unsafe to place a lot of confident physical bounds on what advanced civilizations will be able to do. Here’s an example that may turn into the start of a series.

Mirror matter is made of particles that are in a sense normal matter’s mirror image. Some physicists think it exists, perhaps even in large enough quantities to play a role in astronomy. Mirror matter would be invisible, but would behave like normal matter gravitationally, and might still interact weakly with normal matter. Robert Foot, a physicist who’s studied mirror matter, has written a book on it, part of which is on the web.

Note well: mirror matter is not antimatter is not negative mass is not matter-in-parallel-worlds.

If mirror matter exists in significant amounts, the possibilities get crazy. It’s been suggested that the Tunguska event was the impact of a body made of mirror matter, some of which is still in the ground and could be recovered by an expedition. Exoplanets could be made of mirror matter. There could be mirror stars. There could even be mirror planets in our own solar system. Some have speculated that perhaps Pluto or some moons of Jupiter are made of mirror matter with a small crust of normal matter, so that if you went there and dug down, they’d seem hollow, but you could mine the stuff.

Why would you want to collect mirror matter? There are probably a lot of different applications. Perhaps the most interesting is free energy. The mirror world, not having a mirror sun, is very cold. From any temperature difference, you can extract work at the cost of letting heat move from hot to cold. We couldn’t keep cooling the real world and heating up the mirror world forever, but we could do so for a long, long time.

If this isn’t classic mad science, I don’t know what is.

The verdict: P < .1. (I’m going purely by authority — it’s clearly legit science, but also clearly a minority view.)

But if true, incredibly cool.