Discussion in 'Physics & Math' started by arfa brane, Apr 9, 2018.
Anybody read The Cat Who Walks Through Walls ?
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Yeah. That and Time enough for Love, The Number of the Beast, and To Sail beyond the Sunset. All of which are interconnected in some way.( There are also connections to The Moon is a Harsh Mistress and The Rolling Stones ( among other Heinlein novels).
Mainstream science no longer believes in the deterministic concepts of the 1800's.
The current belief is that the classical world of our senses is based on a quantum level of reality which is probabilistic rather than deterministic.
I read a bunch of Heinlein novels. I think I started too late. I found a lot of it irritating.
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I've tossed more than one book because I thought the author was full of it.
If a time travel device is some day invented, it might become more useful as a space traveling device, unless it was accompanied by movement in space.
Suppose the device took me circa 30 days into the past. If I remained in the same place, I would be a long way from the Earth of 30 days ago .
Note that the typical time travel paradoxes might not be possible. If I went back to the time when my grandfather was 10 years old, I would far away from that 10 year old version of him unless the device also moved me spatially.
Four dimensional tracking would be required, most certainly, begging the question "How do we get that data?"
I have a suspicion that any time travel device would be limited to travel over the span of time that the time machine itself is in existence. You would enter the time machine at some point of its time line and exist it at another point of its timeline.
This solves two problems:
It explains why we do not now have any time travelers visiting from the future now.
It takes care of the movement in space problem*. You just appear where the time machine is at that time. ( However, there may be other issues in play. Is momentum conserved? if so what happens when you transport back by 6 months and appear with a velocity some 60 km/sec relative to the machine itself.)
* The movement in space issue is, in of itself, a bit of a head-scratcher. Movement relative to what? Since there is no absolute frame of rest by which to measure motion, there is no way to say how much the Earth "moved" over those 30 days in any absolute sense.
You have to admit that we're a good ways away from where we were when you were born, right?
Again, relative to what?
The speed at which the Sun (and the rest of the Solar System) move relative to the average of the nearby stars. This speed is at the moment about 20 km/s or 72,000 km/h, but can change in the future because of the gravity of other stars that the Sun may pass on its travels.Apr 24, 2017
Astronomy Answers: AstronomyAnswerBook: Motion of the Earth
In the non-specific sense of how it's mutably implemented in different fiction, "temporal migration of consciousness" is potentially an old idea dating back at least to John Wyndham's Consider Her Ways (if not well before). The Alfred Hitchcock Hour did a version of the short-story in 1964. (video clip)
Novikov Self-Consistency Principle: "Asserts that if an event exists that would cause a paradox or any *change* to the past whatsoever, then the probability of that event is zero. It would thus be impossible to create time paradoxes."
Since time-travel is speculation anyway, back in the March 1994 issue of Scientific American, David Deutsch's The Quantum Physics of Time Travel(PDF) took a stab how consistency could be preserved in the context of non-classical physics. Today, experiments stemming from Seth Loyd's views seem to indeed indicate that information sent into the past could only yield outcomes which maintained consistency (or only particles which did not contradict their own origins or existence could successfully time-travel).
The team found that only those photons that wouldn’t lead to paradoxes made it through unscathed. Although the result is in line with expectation, no one has simulated time travel in this way before. An odd consequence of post-selection is that because the presence of a CTC annuls paradoxical states completely, it can disallow some states that seem innocuous today but have unacceptable consequences later. “In principle, one could detect the future existence of time machines by … looking for deviations now from the predictions of quantum mechanics,” says Todd Brun of the University of Southern California in Los Angeles. Although, he adds, it’s hard to know in advance what to measure."
Time travel experiment demonstrates how to avoid the grandfather paradox (2011)
Time Travel without Regrets (2011)
Time Travel Simulation Resolves “Grandfather Paradox” (2014)
"Relative to the average of the nearby stars" is a reference of convenience, not one against which absolute motion can be judged . You could just as easily choose the Solar system's motion relative to the Galaxy's center, or our galaxy's motion with respect to the center of mass for the local group, or our motion with respect to the CMBR. The point is that none of these references are "special". None of them can be considered THE reference against which the Earth's motion is measured. When there are an infinite number of equally valid reference frames from which you can measure the motion of the Earth, how do you justify using one over any of the others?
You may quibble as much as you like.
Quibbling? That is the nature of relativity. There is no preferred reference frame.
Certainly the local group of stars is not a preferred reference frame. How many? The closest 10? The closest 20? If I make it 21 instead of 20, the velocity changes.
How is pointing out something that is fundamental to the very nature of the universe quibbling?
The Door into Summer is another interesting Heinlein Time travel story.
Yeah, and a good "revenge is sweet" as well.
In all the so-called resolutions proposed there not involving traveling somewhere else i.e. 'parallel universes', it's assumed either CTC's are possible (requiring GR to be fully self-consistent - it aint), or restrict to very simple quantum interactions where degrees of freedom are at the binary level. Try transporting even one complex molecule say a protein, and watch the argument fall apart. Further, such simple scenarios neglect that the mere presence of even one particle from the future will gravitationally effect it's surroundings. Unavoidably then altering the future state of the universe. All still bunkum.
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