Living in Many Worlds

Eliezer Yudkowsky5 Jun 2008 2:24 UTC
61 points
80 comments5 min readLW linkArchive

Some commenters have recently expressed disturbance at the thought of constantly splitting into zillions of other people, as is the straightforward and unavoidable prediction of quantum mechanics.

Others have confessed themselves unclear as to the implications of many-worlds for planning: If you decide to buckle your seat belt in this world, does that increase the chance of another self unbuckling their seat belt? Are you being selfish at their expense?

Just remember Egan’s Law: It all adds up to normality.

(After Greg Egan, in Quarantine.[1])

Frank Sulloway said [2]:

Ironically, psychoanalysis has it over Darwinism precisely because its predictions are so outlandish and its explanations are so counterintuitive that we think, Is that really true? How radical! Freud’s ideas are so intriguing that people are willing to pay for them, while one of the great disadvantages of Darwinism is that we feel we know it already, because, in a sense, we do.

When Einstein overthrew the Newtonian version of gravity, apples didn’t stop falling, planets didn’t swerve into the Sun. Every new theory of physics must capture the successful predictions of the old theory it displaced; it should predict that the sky will be blue, rather than green.

So don’t think that many-worlds is there to make strange, radical, exciting predictions. It all adds up to normality.

Then why should anyone care?

Because there was once asked the question, fascinating unto a rationalist: What all adds up to normality?

And the answer to this question turns out to be: quantum mechanics. It is quantum mechanics that adds up to normality.

If there were something else there instead of quantum mechanics, then the world would look strange and unusual.

Bear this in mind, when you are wondering how to live in the strange new universe of many worlds: You have always been there.

Religions, anthropologists tell us, usually exhibit a property called minimal counterintuitiveness; they are startling enough to be memorable, but not so bizarre as to be difficult to memorize. Anubis has the head of a dog, which makes him memorable, but the rest of him is the body of a man. Spirits can see through walls; but they still become hungry.

But physics is not a religion, set to surprise you just exactly enough to be memorable. The underlying phenomena are so counterintuitive that it takes long study for humans to come to grips with them. But the surface phenomena are entirely ordinary. You will never catch a glimpse of another world out of the corner of your eye. You will never hear the voice of some other self. That is unambiguously prohibited outright by the laws. Sorry, you’re just schizophrenic.

The act of making decisions has no special interaction with the process that branches worlds. In your mind, in your imagination, a decision seems like a branching point where the world could go two different ways. But you would feel just the same uncertainty, visualize just the same alternatives, if there were only one world. That’s what people thought for centuries before quantum mechanics, and they still visualized alternative outcomes that could result from their decisions.

Decision and decoherence are entirely orthogonal concepts. If your brain never became decoherent, then that single cognitive process would still have to imagine different choices and their different outcomes. And a rock, which makes no decisions, obeys the same laws of quantum mechanics as anything else, and splits frantically as it lies in one place.

You don’t split when you come to a decision in particular, any more than you particularly split when you take a breath. You’re just splitting all the time as the result of decoherence, which has nothing to do with choices.

There is a population of worlds, and in each world, it all adds up to normality: apples don’t stop falling. In each world, people choose the course that seems best to them. Maybe they happen on a different line of thinking, and see new implications or miss others, and come to a different choice. But it’s not that one world chooses each choice. It’s not that one version of you chooses what seems best, and another version chooses what seems worst. In each world, apples go on falling and people go on doing what seems like a good idea.

Yes, you can nitpick exceptions to this rule, but they’re normal exceptions. It all adds up to normality, in all the worlds.

You cannot “choose which world to end up in.” In all the worlds, people’s choices determine outcomes in the same way they would in just one single world.

The choice you make here does not have some strange balancing influence on some world elsewhere. There is no causal communication between decoherent worlds. In each world, people’s choices control the future of that world, not some other world.

If you can imagine decisionmaking in one world, you can imagine decision-making in many worlds: just have the world constantly splitting while otherwise obeying all the same rules.

In no world does two plus two equal five. In no world can spaceships travel faster than light. All the quantum worlds obey our laws of physics; their existence is asserted in the first place by our laws of physics. Since the beginning, not one unusual thing has ever happened, in this or any other world. They are all lawful.

Are there horrible worlds out there, which are utterly beyond your ability to affect? Sure. And horrible things happened during the twelfth century, which are also beyond your ability to affect. But the twelfth century is not your responsibility, because it has, as the quaint phrase goes, “already happened.” I would suggest that you consider every world that is not in your future to be part of the “generalized past.”

Live in your own world. Before you knew about quantum physics, you would not have been tempted to try living in a world that did not seem to exist. Your decisions should add up to this same normality: you shouldn’t try to live in a quantum world you can’t communicate with.

Your decision theory should (almost always) be the same, whether you suppose that there is a 90% probability of something happening, or if it will happen in 9 out of 10 worlds. Now, because people have trouble handling probabilities, it may be helpful to visualize something happening in 9 out of 10 worlds. But this just helps you use normal decision theory.

Now is a good time to begin learning how to shut up and multiply. As I note in Lotteries: A Waste of Hope:

The human brain doesn’t do 64-bit floating-point arithmetic, and it can’t devalue the emotional force of a pleasant anticipation by a factor of 0.00000001 without dropping the line of reasoning entirely.

And in New Improved Lottery:

Between zero chance of becoming wealthy, and epsilon chance, there is an order-of-epsilon difference. If you doubt this, let epsilon equal one over googolplex.

If you’re thinking about a world that could arise in a lawful way, but whose probability is a quadrillion to one, and something very pleasant or very awful is happening in this world . . . well, it does probably exist, if it is lawful. But you should try to release one quadrillionth as many neurotransmitters, in your reward centers or your aversive centers, so that you can weigh that world appropriately in your decisions. If you don’t think you can do that . . . don’t bother thinking about it.

Otherwise you might as well go out and buy a lottery ticket using a quantum random number, a strategy that is guaranteed to result in a very tiny mega-win.

Or here’s another way of thinking about it: Are you considering expending some mental energy on a world whose frequency in your future is less than a trillionth? Then go get a 10-sided die from your local gaming store, and, before you begin thinking about that strange world, start rolling the die. If the die comes up 9 twelve times in a row, then you can think about that world. Otherwise don’t waste your time; thought-time is a resource to be expended wisely.

You can roll the dice as many times as you like, but you can’t think about the world until 9 comes up twelve times in a row. Then you can think about it for a minute. After that you have to start rolling the die again.

This may help you to appreciate the concept of “trillion to one” on a more visceral level.

If at any point you catch yourself thinking that quantum physics might have some kind of strange, abnormal implication for everyday life—then you should probably stop right there.

Oh, there are a few implications of many-worlds for ethics. Average utilitarianism suddenly looks a lot more attractive—you don’t need to worry about creating as many people as possible, because there are already plenty of people exploring person-space. You just want the average quality of life to be as high as possible, in the future worlds that are your responsibility.

And you should always take joy in discovery, as long as you personally don’t know a thing. It is meaningless to talk of being the “first” or the “only” person to know a thing, when everything knowable is known within worlds that are in neither your past nor your future, and are neither before or after you.

But, by and large, it all adds up to normality. If your understanding of many-worlds is the tiniest bit shaky, and you are contemplating whether to believe some strange proposition, or feel some strange emotion, or plan some strange strategy, then I can give you very simple advice: Don’t.

The quantum universe is not a strange place into which you have been thrust. It is the way things have always been.

1. Greg Egan, Quarantine (London: Legend Press, 1992).

2. Robert S. Boynton, “The Birth of an Idea: A Profile of Frank Sulloway,” The New Yorker (October 1999).

Eliezer Yudkowsky5 Jun 2008 2:24 UTC
61 points
80 comments5 min readLW linkArchive