The "strong anthropic principle" is far more controversial. What is this theory?
The strong anthropic principle says that the universe must bring forth life and observers at some stage. So even if there's only one universe, it must be the case that this universe will end up being observed by beings such as ourselves. Now, that's much harder for scientists to swallow because it seems to turn everything upside down. Most scientists think that the universe came into existence by some happy coincidence, or maybe from this multiverse selection there were beings who emerged. But these beings don't play a central role even in the multiverse theory. They don't play a creative role, whereas in the strong anthropic principle, the observers are in the central position. They are the ones dictating how the universe is put together. And that seems too much for people to swallow. It gives mind and consciousness a central place in the great scheme of things.
Well, it sounds fairly religious. Let's face it, the most common explanation for how all of this happened is that God set the process in motion so that human beings could eventually evolve.
You could give this either a religious or an anti-religious interpretation. The religious interpretation is that God made the universe just as it is in order that life and conscious beings could emerge. The other way, which I suppose would be anti-religious, is to say that the emergence of life and observers causes the universe to have the laws that it does. In the causal sense, it puts the cart before the horse. It makes the emergence of life and observers later on in the universe have some responsibility for the way the laws come into being at the beginning.
Is this what John Wheeler, the famous theoretical physicist, talked about when he made the case for a "participatory universe"?
Yes. Now we're into another variant of the anthropic principle -- which is sometimes called the "final anthropic principle" -- where, somehow, the emergence of life and observers link back to the early universe. Now, Wheeler didn't flesh out this idea terribly well, but I've had a go at trying to extend it. This has some appeal because the conventional theistic explanation and the conventional scientific explanation both suffer from the same shortcoming. They attempt to explain the universe by appealing to something outside it. In the religious explanation, appeal is made to an unexplained God who simply has to be there in order for the universe to be created in the form that it has. In the scientific explanation, the laws of physics just happily exist for no particular reason, and they just happen to have exactly the right properties, but it's all unexplained and it's all pushed off to outside of the universe. What appeals to me about John Wheeler's idea is that it attempts to provide an explanation for the bio-friendliness of the universe from entirely within it. Now, the difficult point is that we have to explain why life today can have any effect on the laws that the universe emerged with at the time of the big bang.
This sounds like it's coming right out of science fiction. Somehow, future people can go back in time and have some role in creating the universe. It's pretty far-fetched.
It is pretty far-fetched until you stop to think that there is nothing in the laws of physics that singles out one direction of time over another. The laws of physics work forward in time and backward in time equally well. Wheeler was one of the pioneers of this underlying time symmetry in the laws of physics. So he was steeped in the fact that we shouldn't be prejudiced between past and future when it comes to causation. The particular mechanism that Wheeler had in mind has to do with quantum physics. Now, quantum physics is based on Heisenberg's uncertainty principle. In its usual formulation, it means that there's some uncertainty at a later time how an atom is going to behave. You might be able to predict the betting odds that the atom will do this or that, but you can't know for certain in advance what's going to happen. Now, this uncertainty principle works both ways in time. There's no doubt about this. If we make an observation of an atom in a certain state now, then its past is uncertain just as its future is uncertain.
So one way to think about this is that there will be many past histories that will lead up to the present state of the universe. In the remote past, its state was fuzzy. Now in the lab, it's all very well to put an atom in a certain state and experiment on it at a later time. But when we're applying quantum physics to the whole universe, we simply can't establish the universe in a well-defined quantum state at the beginning and make observations later. We're here and now. So we can only infer backward in time. It's part of conventional quantum mechanics that you can make observations now that will affect the nature of reality as it was in the past. You can't use it to send signals back into the past. You can't send information back into the past. But the nature of the quantum state in the past can't be separated from the nature of the quantum state in the present.
So you're not talking about super-smart beings in the far future who go back in time and somehow fiddle with the laws of physics to create the big bang. You're saying this happens just through the act of observation itself, through the fact that human beings or other intelligent beings are aware of the universe.
Right. I'm not talking about time travel. This is just standard quantum physics. Standard quantum physics says that if you make an observation of something today -- it might just be the position of an atom -- then there's an uncertainty about what that atom is going to do in the future. And there's an uncertainty about what it's going to do in the past. That uncertainty means there's a type of linkage. Einstein called this "spooky action at a distance."
But what's so hard to fathom is that this act of observation, which has been observed at the subatomic level, would affect the way matter spread right after the big bang. That sounds awfully far-fetched.
Well, it's only far-fetched if you want to think that every little observation that we perform today is somehow micromanaging the universe in the far past. What we're saying is that as we go back into the past, there are many, many quantum histories that could have led up to this point. And the existence of observers today will select a subset of those histories which will inevitably, by definition, lead to the existence of life. Now, I don't think anybody would really dispute that fact.
What I'm suggesting -- this is where things depart from the conventional view -- is that the laws of physics themselves are subject to the same quantum uncertainty. So that an observation performed today will select not only a number of histories from an infinite number of possible past histories, but will also select a subset of the laws of physics which are consistent with the emergence of life. That's the radical departure. It's not the backward-in-time aspect, which has been established by experiment. There's really no doubt that quantum mechanics opens the way to linking future with past. I'm suggesting that we extend those notions from the state of the universe to the underlying laws of physics themselves. That's the radical step, because most physicists regard the laws as God-given, imprinted on the universe, fixed and immutable. But Wheeler -- and I follow him on this -- suggested that the laws of physics are not immutable.
I'm trying to understand how the laws of physics could change. You're suggesting that they were different 10 billion years ago. How could they change through the act of observation?
I have to explain my point of view in relation to the laws of physics. In the orthodox view, the laws are regarded as just unexplained, fixed, idealized mathematical relationships. It's an idea that goes right back to Newton-- that the universe is governed by these infinitely precise mathematical laws.
This is basically the Platonic view of the universe.
Plato had the view that mathematics lies outside of the physical universe, in a realm that's not part of space and time. It's often called the "Platonic heaven." But there's another view of the laws of physics, which is gaining increasing currency, that has really come about because of the information revolution. So a lot of physicists think that we should regard the laws of physics not as perfect, immutable mathematical forms that just happen to exist for no reason in this Platonic realm, but rather that they're more like computer software.
Let me explain that. When the Earth goes around the sun, we can imagine applying Newton's laws to predicting how it's going to move. That's just like a computer algorithm. If we know the position and motion of the Earth today, we can compute its position and motion this time next year. So the laws of physics could be thought of like a computer algorithm, taking input data, processing it and delivering output data. That inevitably leads to the analogy that the universe is really a gigantic computer. And many people are enamored of that idea.
So basically, information is all there is in the universe.
That's right. The universe is just a big information processor. Wheeler calls this "it from bit." Now if you take that view -- that the universe is a gigantic computer -- then it leads immediately to the conclusion that the resources of that computer are limited. The universe is finite. It's finite because the speed of light is finite. There's been a finite time since the big bang. So if we have a finite universe, we have a computer with finite resources, and hence, finite accuracy. So once you recognize that the universe is a gigantic computer, then you see that the laws of physics can't be infinitely precise and perfect. There must be a certain amount of wiggle room or sloppiness or ambiguity in those laws.
And the key point here is that the degree of error, which is inherent in the laws, depends on time. As the universe gets older, there are fewer errors because it's had longer to compute. If you go back to the first split second after the big bang, then the underlying errors in the laws of physics really would have been very large. So instead of thinking of the universe as beginning magically with a bang, and the laws of physics being imprinted magically on the universe with infinite precision right from the word go, we must instead think of the laws as being emergent with and inherent in the universe, starting out a little bit vague and fuzzy, and focusing down over time to the form that we see today.
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