Cheating the Causal Game
A new quantum framework that blurs cause-and-effect at a fundamental level could improve information processing and lead to a theory of quantum gravity. [...] From an early age we take the cause and effect of events happening in time for granted; it’s how we think. Without cause and effect, where would science be? We could not attempt to predict the outcome of experiments to test ideas about the world, or try to formulate such theories of what will happen. Even the math that describes the atomic world—quantum theory—assumes that events take place in time in an ordered and connected fashion. Which makes it all the more strange that some physicists are trying to ditch this neat time-ordering.
This is by no means an obvious strategy to employ, notes Caslav Brukner, at the University of Vienna, Austria, one of the physicists behind the idea. "It’s simply new physics," he says. "We are asking whether space, time and causal order are truly fundamental ingredients of nature." The team hopes that by taking an approach that doesn’t rely on causal structure, it might provide a clue about where causal order comes from. Is it a necessary property of nature or can it be derived from more primitive concepts? [...]
Q&A with Paul Davies: What is Time?
[...] The flow of time is an illusion, and I don’t know very many scientists and philosophers who would disagree with that, to be perfectly honest. The reason that it is an illusion is when you stop to think, what does it even mean that time is flowing? When we say something flows like a river, what you mean is an element of the river at one moment is in a different place of an earlier moment. In other words, it moves with respect to time. But time can’t move with respect to time—time is time. A lot of people make the mistake of thinking that the claim that time does not flow means that there is no time, that time does not exist. That’s nonsense. Time of course exists. We measure it with clocks. Clocks don’t measure the flow of time, they measure intervals of time. Of course there are intervals of time between different events, that’s what clocks measure. [...]
Dreaming The Dream
[...] What worries cosmologists is not so much the possibility that we might all be Boltzmann brains dreaming unreal dreams about the world around us. Nobody seriously believes that. Cosmologists build theories about the Universe and how it evolves. In other areas of science, when you have come up with a theory (say about the behaviour of mice) you then set up an experiment (observe many mice) to see if your theory fits with observations. If it does, good, if not, you need to improve the theory, or throw it out. But since it's impossible to replicate our Universe in a lab, cosmologists can't do this. They need to come up with other ways of finding out whether a theory is plausible.
This is where Boltzmann brains come in. Once you have constructed a theory about the Universe you can calculate the probability that certain types of observers (including Boltzmann brains) come into existence. If the calculation suggests that we are overwhelmingly likely to be Boltzmann brains, rather than the good and honest observers we know we are, then that's an indication that something about the theory, or the assumptions you made in your probability calculation, is wrong. [...]
Why does cosmology need philosophy?
[...] Cosmologists have developed the multiverse theory for good reasons (see this Plus article). But as Ellis says: "There's absolutely no direct evidence and it never will be possible to get direct evidence. If you can't test the theory you have to say, 'Is this now a scientific proposal or a philosophical proposal?' In my view this is scientifically inspired philosophy, not science, because I think you should draw a hard line."
In view of this untestability some people have suggested that we should weaken the requirements of science. 'If we have a really strong theoretical argument, [people have suggested] we should say, 'It's so good, we no longer need to test it in the way we've taken for granted up to now,'"explains Ellis. "I think that's very dangerous and I think it would allow all sorts of pseudo-sciences to be reclassified as science. I don't think we want to see that happen." [...]
If you pulled on a rope a mile long, how long would it take for the pull to reach the other end. Or would the pull be instantaneous?