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Cosmologist Carlo Rovelli: Future time travel only a technological problem


Not a scientific one. Dan Falk interviews physicist Carlo Rovelli about “about the nature of time, whether it has a beginning and if humans might one day master time travel:”

Carlo Rovelli

Could time travel ever be possible?

Well, “time traveling” is what we do all our lives, isn’t it? But you mean, can we jump quickly to the past or to the future. Jumping to the far future is certainly possible. It’s only a technological problem, not a scientific one.

One way is to move very fast. When you move fast, time passes very slowly for you — so if you could run fast enough around your house many times, you could do that in a time span which for you is a couple of minutes, but in the meanwhile centuries pass for everyone else. The only difficulty is that the speed needed for this has to be very high, comparable to the speed of light.

Another way to jump to the future is to travel near a black hole. Near a black hole, time slows down. So a starship could wait there for half an hour and then move away from the black hole, and find itself millennia in the future.

What about traveling back in time?

That’s much more complicated. It is not logically impossible, but it requires beating the second law of thermodynamics, which would be like beating the laws of probability. I think that if we ever achieve this, it would be long after we’ve mastered forward time travel.Dan Falk, “Physicist Carlo Rovelli ponders the enigmatic fourth dimension” at NBC News

While we are here, philosopher of science Robert Crease writes critically of Rovelli’s new book, Carlo Rovelli’s The Order of Time:

For centuries, philosophers and scientists have been tempted to seek some seemingly permanent, unchanging stuff in experience – quantum fields, say – that give rise to everything else, including human experience, and name this the “real”. The trouble with the “reality trick” is not just that we keep changing our minds about the fundamental stuff. It also downgrades the importance of everything else, most notably our lived experience. Rovelli seems to recognize this in a chapter on how language can promote certain erroneous assumptions about reality and existence. Still, it is all too tempting to revert to language that suggests that storms and supernovae are not real but merely epiphenomena.

You can’t explain time by putting physicists in charge of “what time really is” and then trying to stitch this together with experienced time. That inevitably results in experienced time having a secondary status – discussed only in humanities courses that get axed from the curriculum when the next budget crisis hits. The task for philosophers of time is to explain that physicists’ conceptions of time are highly selective, mathematized ideas that are useful, but grow out of human concerns that arise in experienced time. Robert Crease, “Fooled by Time” at Physics World

See also: Does physics deconstruct our sense of time? At Nature, Andrew Jaffe reviews Carlo Rovelli’s The Order of Time

Carlo Rovelli: Theories of everything ill-conceived but we can learn to understand quantum mechanics


Cosmologist: Philosophy is essential to the development of physics.

Nothing infuriates me more than hearing mainstream physicists pontificate about time, a subject most of them have zero understanding of. Rovelli: Well, “time traveling” is what we do all our lives, isn’t it? No it isn't. Nothing travels in time in any direction. We are always in the present, the every changing present. It is simple to prove that time travel is nonsense. Any kind of movement requires a rate of change, i.e., a speed. Normal speed is computed as v = ds/dt. Movement in time, if it exists, is no exception. The speed of motion in time would have to be given as v = dt/dt = 1, which is nonsensical since 1 is not a speed. And no, it is not 1 second per second. It is 1 and it's nonsense. Conclusion: Rovelli is a crackpot. But he's not alone, the recently deceased little guy in the wheelchair was famous for his belief in time travel. Such is the state of modern physics, a mountain of bovine excrement. FourFaces
I keep telling my colleagues that we should start a time-travel project. Then I remember that it doesn't matter when your time-travel project finishes. Then I remember that it doesn't matter when it starts. And then I forget about it again. ScuzzaMan
Spacetime is still not properly understood. Time is emergent in a very physical way, and it makes the flow of energy one-way. This is all just wishful thinking---another "just-so" story in the making. PaV

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