Italy just had their LARES-2 satellite launched. It's purpose is to carefully measure the frame dragging predicted by Einstein's theory. https://en.wikipedia.org/wiki/Frame-dragging The satellite is unpowered and seriously dense, like a beach ball weighing 870 lbs. It's heavy in order to make the atmosphere less of an issue in its travel. It's orbit will be carefully measured by lasers from Earth. Frame dragging has been measured in the past, but there are differences in the measurements. This experiment includes the speed of the object as it orbits the rotating mass of Earth. https://ilrs.gsfc.nasa.gov/missions/satellite_missions/current_missions/lars_general.html Some folks believe Einstein's theory hasn't be tested. I like to point out that it's being tested ALL THE TIME and in many different ways.
And has been for over a century now. Frame dragging is why you can make a time machine out of a black hole. Circumnavigate a black hole at the proper speed and distance, and when you get back to the point you entered, it will also be the moment you entered. You will have gone back in time to the starting point. So you had better be sure you don't run into yourself! Hey, that would be a great test of causality that we could actually do now if we could get to a black hole. Send a probe and do that very test. Can the probe be made to hit itself, thus preventing it from circumnavigating the black hole, when it must have done so to hit itself.
A famous Russian physicist named Igor Novikov did a logical proof showing that the probe could not hit itself - he actually does the thought experiments using a billiards table with a hypothetical time machine in one of the pockets. But he concluded that a ball cannot be made to interfere with itself enough to change the binary outcome - did it hit or miss the pocket. It could deflect itself a bit but not enough to miss the pocket and violate causality. So we might expect that we could not cause the probe to destroy itself. But that was not a hard proof. We don't know. Maybe we run the experiment, the probe self destructs, and the stars all start blinking out...
The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture and Larry Niven's law of conservation of history, is a principle developed by Russian physicist Igor Dmitriyevich Novikov in the mid-1980s. Novikov intended it to solve the problem of paradoxes in time travel, which is theoretically permitted in certain solutions of general relativity that contain what are known as closed timelike curves. The 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. https://en.wikipedia.org/wiki/Novikov_self-consistency_principle Note that Larry Niven is a science fiction author. So a law for Larry isn't a law in science. It is just a great concept to use in sci fi. For Novikov [a scientist] it is conjecture.
Now that I think about it, we do have a hard proof of what happens. It comes from the calculations in General Relativity. So apparently we can cause the probe to hit itself, thus preventing it from circumnavigating the black hole and hitting itself... That is what the hard derivation says. So Novikov was just looking for some rationale to reject the derivation and the incomprehensible outcome. It's a freaking mystery!!!
Maybe we think too much. Maybe it does destroy itself and the paradox only remains in our minds. For some reason, the universe is fine with this. That seems to be what the physics says. Honest to god, that is a solution I don't think I've ever heard before. And it is simple. But causality preservation is considered to be more fundamental than energy conservation.
I can't stop thinking about this. For nearly a century we have assumed that contradictions cannot occur. The probe can't destroy itself if it has a history. It has to be consistent. We have assumed that Novikov is right. But it is consistent with the temporal anomaly. If you introduce the temporal variance due to frame dragging, then there really is no contradiction if the probe destroys itself. Why do we need a better explanation? All of this arm waving about violating causality really don't apply. We know the cause and the events occurred in the order they should according to General Relativity. It all makes perfect sense. I need to run this by the physics crowd and see what kind of response I get. I don't recall ever hearing this argument and it almost seems obvious now. What have we been so worried about? Why can't things occur exactly as predicted by GR, seeming contradictions and all? It is consistent with the physics and that's all that really matters.
I'm sure the problem comes up when you try to draw the world line for the probe. But I haven't done some of this since I was in college. And even then it was a brain buster. As a buddy once stated, tensors make me tenser.
Haha. I don't think that would apply. If in orbit you feel no gravity; just like on the space station. But that is one of my favorite effects.
I agree. But what if you hit yourself and explode? You might get stuck in an H Mobius Loop like the NCC-1701-D Enterprise did. And you wouldn't have Data to save you!
More fun facts about black holes. Clocks run slowly in gravity fields. So as you approach a black hole, someone watching would see your clocks running more and more slowly as you approach the event horizon. In fact they run so slowly when you get very close, as you are being ripped to pieces by the tidal forces of gravity, someone watching would effectively see you frozen in time in a frozen scream. I like to call it the eternal scream.
Another fun fact If you could go beyond the event horizon in a black hole that conforms to the Schwarzschild metric https://en.wikipedia.org/wiki/Schwarzschild_metric if you hit your thrusters to change your position in space, instead you would change your position in time. Time and space reverse roles.
I don't know if time travel is possible; it doesn't seem to make sense, but there are more things in heaven & Earth... Nevertheless, the theories we currently have about time travel, definitely seem wrong. First, it should be noted that many prominent physicists (including Hawking, when he was alive), maybe even the majority of them, do not believe travel backward in time is possible. There is the famous example of the ridiculous scenario, if such a thing were possible, of someone going backwards in time by a minute to meet his former self, and then them waiting a minute before returning, to pick themselves up, making it a group of four selves, then 8, then 16, ad infinitum. So any who want to bash me as just some guy on the internet, should know that there are serious doubts, among the scientific community, as well. That taken care of, what all the examples I hear, based on Einstein's work, seem to focus on, is the changing of the subject's perception of time, which then gets faultily transmuted into the idea that this affects time, itself-- BALDERDASH! If the speed of one's metabolic processes, changed the speed of time, this would mean that actual time would slow down (or would one's own slowing down make time speed up?) for someone freezing to death. It would mean that mosquitos would travel through time at a different speed than humans. But all we are really talking about are perceptions of time, not actual time. Simple experiment: put a human, a mosquito, & a sloth, simultaneously into an observation chamber. When, at some future point, they all are brought out, together, is it not but a single moment, which all three are sharing? Likewise, the entire time, locked up together, was exactly the same amount, by any objective measurement, for all three. The only difference would be how each experienced that time. Better yet, put a Mayfly in there for 12 hours, half of its life in its adult form-- and yet, for some humans, that's barely more than the time they may spend, trying to sleep off a hangover. So I really think, when people start talking about something meeting itself, they are speaking about science fiction, more than they truly are, about science.
Physicists point out that for every individual, wherever they are, whatever they are doing, however fast they are going, however massive they are, whatever acceleration they are experiencing, etc., time passes (as they can see by the clock they brought along) at exactly one second per second. So, for each individual, that is what we experience - one second per second. Yet, what is observed is that clocks that are in different situations do not always compare as equal. For example, time comparisons between Earth and the ISS are different by approximately 0.01 seconds for every 12 Earth months passed. That is known, because it is easily measured - it's not just theoretical. The reason has to do with the fact that the ISS is being accelerated according to the mass of Earth, as noted by the fact that the ISS is traveling in a curved path. Still, time is passing at one second per second for those on the ISS and for those on Earth. That is what incredibly accurate clocks say.
Or here's a possibility-- though it may seem less likely to you, than simply speeding up time: what if the acceleration effect is speeding up the atomic processes, of those incredibly accurate clocks, just as it does the biological processes of those onboard? In that case, all it would be doing is aging the space station's occupants, slightly faster than normal. Of course, for those in a hurry to age, there are all kinds of activities to which one can turn, that will do the job more easily, than needing to get up into space: take up smoking, for example. Here's the thing, Will. When those people return from the ISS, there is no reason to believe they are not sharing the same moment of "time," with people who they'd left, back here on Earth. They are not now 0.01 seconds "ahead" of everyone else, in time. People do not say, when asked of their whereabouts, "I saw him just 60.01 seconds ago," instead of, a minute ago. So, at the very most, one might claim they got 0.01 seconds more "time," in effect, jammed into the time which they had experienced. But it was a local effect: everyone else's time remained constant; and that larger timeline is what they rejoined, at the exact same spot they would have, had they not been accelerated. Again, a similar effect can be duplicated, at least in its results-- if not by actually stretching time itself, by that tiny fraction of a second-- by someone's snorting cocaine, taking amphetamines, or slamming meth: you will be able to do more, in the same amount of "time," though, if it is the last of those aforementioned options which is chosen, I would not anticipate that one's "extra time," would be especially productive time.
@WillReadmore Let me add one more thing. As I'd previously suggested, it is a known fact that increased temperature increases molecular activity (turns water into steam, for example, or hurries the aging & spoilage of food) while reduction of temperature, slows it. Therefore, at sufficiently high & low temperatures, it stands to reason that atomic processes can also be affected. Who knows, perhaps the removing of all resistance from extremely cold superconductors, is a function of their stepping outside of the same temporal strictures of the things around them. But this does not mean that they now exist, "in the future." Do you follow me? IOW, of we are to regard "Time," as a physical thing, not just a human construct, then one must include the possibility of that physical thing being non uniform, in all its parts, of being malleable. But just because one softens a specific part of some metal object, then stretches it out, through pounding it, i.e, through exerting pressure on it, does not mean that this stretching affects any part of the object, other than the part heated, and "banged."
@WillReadmore To, I hope, not put too fine a point on it: Einstein was a little overly fond of his static pictures, of his pronouncements of things being unchanging. Since light, for example, is electromagnetism, it seems illogical to me, to assume that, subjected to sufficient magnetic forces, for instance, one could not alter the speed of light, at least as it, locally, passed through those forces. In fact, it is already assumed that light cannot escape the gravity of a black hole-- so much for its speed being a "constant." That is only so, under ordinary conditions. I am suggesting that the very same thing may be true of "time." And just as the slowing of light, in some given place, due to some extraordinary circumstance, has no effect on light elsewhere, so might the acceleration/deceleration of the speed of time, only have its effects on things within the area affected by the stimulus (of speed, in this case), without affecting the flow of time elsewhere. Hence, once one is removed from the time- changing stimulus, they are no further "ahead," in general time, even if they have progressed further along, as a quantum of time, their own, personal, timeline.
When the ISS astronauts return, their personal clocks are not the same as those who stayed on Earth. Yes, the difference isn't large, even when they stay on the ISS for considerable time. They are in near Earth orbit and going very slowly compared to the speed of light. Our universe was shown by Einstein to be space-time, not just space with time being separate. One way to see what's happening is to remember that we can go from point a to point b through our three dimensions of space along different paths - some longer than others. The same is true for space-time as a whole. There are paths through space-time that are longer or shorter than others. The ISS is taking a different path through space-time, thus our clocks aren't going to be the same, even though they tick at one second per second.
Yes, one can definitely affect the speed of light. When considering the cosmic speed limit, the speed of light, what is being referenced is that speed in a pure vacuum and without other forces on it. Nothing can get faster than that. But, light can be slowed down by passing it through liquids, for one example, or by having it pass by a mass, like a star for another example. I don't know of any physics theory that suggests what you are saying about time in the last part of your post.
No, Will, he did not show that space and time were merely different sides of the same coin. He theorized it, and showed how it might be true. But just because he could imagine such a thing, is not proof of his theories, in full. That is because, all-importantly, we can't study "time," as if it were something tangible, and therefore come to any experimental conclusions about how it "behaves." However, if you accept Einstein's theories whole-- without the proper documentation, in the form of reproducible results, as you usually are so keen about first evaluating-- then you must accept that, any way in which physical space can be manipulated, so can time. I think that was kind of his main point, that through substantially affecting one, (space), we affect the other (time). So? What do you think this absolutely proves? But, for both the sake of avoiding our own wasting time, due to unnecessary misunderstandings, as well as for the benefit of the hypothetical reader, who someday may come along and be interested enough, to read our conversation: when you say their "personal clocks," what you are referring to, I am guessing, are not individual's timepieces, but rather an analysis of their biological aging, based largely on the lengths of their telomeres-- the excess, leftover length, to put it simply, of their DNA/genes-- is that correct? Because we can measure different durations of existence, which we call time, does not prove that time is in an interchangeable, two-way relationship with space. And there is the fallacy-- that just because you can imagine an analogy, it must be true! But just because Einstein could compare passing through space-time, to walking through a building, moving to higher floors as he progressed, combined with his ability, in that scenario, to be able to also move back to a lower floor, he had previously ascended from, does not, in any way, prove that this is possible, in the case of time. As I had already noted, most physicists, today, I think now actually doubt this could happen (that one could go back in time). Nevertheless, consider this idea of the atomic/biological clocks, moving faster under certain conditions. One need not even leave the planet, to experience this. The same thing was shown, on Stephen Hawking's awful (IMO) television program, How to Think Like a Genius. One person, among a group of volunteers, drove up from the canyon floor, where his friends would be sleeping, to the top of a mountain. Both groups had these incredibly accurate atomic clocks, to which you've alluded. The next morning, the rest of the group made the drive up to the top, to see their friend, and compare clocks. The clock of the person who'd spent time at the significantly higher elevation, was slightly ahead of the clock that had been at sea level. This was touted as proof that this person had "travelled faster through time." And yet, after spending the better part of a day, "getting ahead of" all those low altitude suckers, his friends were able to catch up, in just the time it took for them to drive up. Because, there they were, in conversation-- which could only occur, if they were at the same point in time. Please consider that thoroughly, as it is central to my argument. In fact, if this acceleration of his clock actually represented a moving ahead in time, even the slightest bit quicker than others, then it would have been easy to disprove Hawking's first point, of the episode I am referencing; because, in his earlier experiment, he showed how geniuses, like himself, understood that travel backward in time, was impossible. Yet, if the guy on the mountain had truly moved an iota ahead, in time, then-- had he gone to the bottom of the mountain, to join his friends, the next day, instead of their coming to him-- he would necessarily be going back in time, to see his friends, who'd not experienced his same "acceleration." Again, anyone who considers this effect as the equivalent of time travelling, just does not understand it. At a higher elevation, the effects of both gravity and atmospheric pressure-- i.e., forces of resistance-- are less. Therefore his biological processes move more swiftly. The clock must be subject to the same atmospheric & gravitational forces. So all this experiment really proves, is that atomic processes can be speeded up (and the inverse, slowing them down, would be, likewise implied) through differing the gravitational forces, and the atmospheric pressure, they are under. Just to reiterate the other thing I said, at the outset: I am not claiming that this is impossible; for nor can I prove that. I am merely saying that, 1) Einstein's theories on space-time have not been fully vindicated, even if some of his equations have proven to be helpful; and, 2) as they have been explained by Einstein, some of his ideas seem rather dubious, not just to me, but to a majority of experts, in this field. It has long been proven that humans, writ large, can totally misperceive even the most straightforward of phenomena. For example, the ancient Greeks, despite their wisdom, were once quite convinced that the wind, was created by trees. It was, in their minds, a self-evident fact, for whenever one sees the trees branches bending, one will surely feel wind.
