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lvlastermind
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I'm interested in knowing anything about time travel into the past. If anyone has any insight about this it would be helpful.
lvlastermind said:I'm interested in knowing anything about time travel into the past. If anyone has any insight about this it would be helpful.
Kerr black holes already are singularities. Anyway, Titor's explanation was basically just technobabble that doesn't make any sense in terms of physics, despite the inclusion of a few buzzwords like "Kerr black hole" that actually are used in physics.oldunion said:I did some research on it a while back because i got interested in John Titor's rhetoric. From what my memory has now, you would have 2 Kerr black holes which would interact with each other in such a way as to form a singularity.
Do you understand what "relative" means?Since we have no idea how fast we are moving through space, even in a relative fashion
To even say that there is a point in space now that uniquely coincides with "the position of the Earth an hour ago", regardless of whether we can know where that point is or not, is to assume the existence of absolute space, in contradiction with relativity. And as PeteSF says, you seem to be misunderstanding what "a relative fashion" would mean, it is certainly possible to say how far the Earth has moved relative to some inertial observer.DrChinese said:One of the most practical issues with respect to "sci-fi" time travel...
Where would you travel to?
Not a simple question at all. Earth rotates, as does the solar system and the Milky Way. So we do not move even close to a straight line. Since we have no idea how fast we are moving through space, even in a relative fashion, it is impossible to estimate where we where an hour ago. So if you went back in time and expected to be on Earth, you better make provision to instead end up in outer space somewhere.
Here's an article from Scientific American by physicist Paul Davies:lvlastermind said:Does anyone know of any websites with information on the possibilities of time travel into the past?
JesseM said:To even say that there is a point in space now that uniquely coincides with "the position of the Earth an hour ago", regardless of whether we can know where that point is or not, is to assume the existence of absolute space, in contradiction with relativity. And as PeteSF says, you seem to be misunderstanding what "a relative fashion" would mean, it is certainly possible to say how far the Earth has moved relative to some inertial observer.
The "same" place relative to some physical landmark like the earth, or the "same" place in some absolute sense?DrChinese said:Just the opposite, I don't mean to imply there is or is not an absolute reference frame. What I said (or meant) was there is no relative position for the Earth to use as an anchor. Presumably, the place I would want to go back to - were I going back in time - would be the "same" place I am now.
Assist in what process? Other observers couldn't find a point that was objectively the same place in a frame-invariant way, but they could certainly find the point that was the same place relative to their own frame--normally when people talk about measuring positions or speeds "in a relative fashion", they mean measuring them relative to a particular observer's rest frame. For example, if you are driving at 50 mph down the road in my rest frame, then in my frame the point you were an hour ago is 50 miles behind your current position, while in your frame the point you were an hour ago is exactly the same as your current position.DrChinese said:I certainly dispute the idea there are observers out there who could assist in this process as they will be just as confused.
What does "effective velocity" mean? If you think there is some absolute, frame-invariant concept of our "effective velocity", then you are saying the theory of relativity is wrong. It's not just a concept of us not being able to obtain enough information to determine it, it's that relativity says that in principle their can be no notion of a velocity that does not depend on an arbitrary choice of reference frame (except for the velocity of light, which is the same in all reference frames).DrChinese said:None of them would be sitting in a preferred position to assist us. Because of the various orbits we are a part of, I doubt we could ever obtain enough information to determine our effective velocity. It is very dynamic.
JesseM said:Kerr black holes already are singularities. Anyway, Titor's explanation was basically just technobabble that doesn't make any sense in terms of physics, despite the inclusion of a few buzzwords like "Kerr black hole" that actually are used in physics.
In your paper you write:oldunion said:Forgive the lacadasical usage of singularity, but it was a "relationship" of some sort between two kerr black holes. I found the paper i wrote about it last semester.
Who are these "some" who believe that the merging of black holes would be the basis for time travel? I have never heard any physicists suggesting such a thing, only John Titor's technobabble.With this laments understanding of physics, let us now observe the possibility that two black holes could theoretically collide. From research being done at the University of British Columbia by Luis Lehner, a representation of what this instance would "look" like has been calculated by a computer. The two black holes would merge into one, and among other events, radiate gravity waves from the area [2]. It is believed by some that this phenomenon is the basis for time travel and that it is possible for it to naturally happen.
What studies? Is the institute in Rhode Island Brown University (where I went to college, coincidentally)? Note that physicists had suggested the possibility of micro-black holes being created in supercollider collisions well before John Titor posted his story, he was no doubt cribbing the idea from something he had read.oldunion said:Also looking into CERN and the institute at rhode island (forget the name) would yield some interesting studies that may take to your liking.
JesseM said:The "same" place relative to some physical landmark like the earth, or the "same" place in some absolute sense? Assist in what process? Other observers couldn't find a point that was objectively the same place in a frame-invariant way, but they could certainly find the point that was the same place relative to their own frame--normally when people talk about measuring positions or speeds "in a relative fashion", they mean measuring them relative to a particular observer's rest frame. For example, if you are driving at 50 mph down the road in my rest frame, then in my frame the point you were an hour ago is 50 miles behind your current position, while in your frame the point you were an hour ago is exactly the same as your current position. What does "effective velocity" mean? If you think there is some absolute, frame-invariant concept of our "effective velocity", then you are saying the theory of relativity is wrong. It's not just a concept of us not being able to obtain enough information to determine it, it's that relativity says that in principle their can be no notion of a velocity that does not depend on an arbitrary choice of reference frame (except for the velocity of light, which is the same in all reference frames).
Your phrasing is still implicitly assuming absolute space--what does "without traversing space" mean? Do you agree that in the example where you are driving down the road at 50 mph in my frame, then in my frame the "same point in space" that you are now is 50 miles ahead of the position your car was an hour ago? Do you agree that in your own rest frame, the "same point in space" that you are now was still inside the car an hour ago? So if you're in the car and you send your body back in time an hour "without traversing space", will you end up still inside the car, or will you end up 50 miles in front of the car? If you think there is a single true answer to the question of where you would end up if you traveled in time "without traversing space", then you are assuming there is a preferred reference frame. After all, in some inertial frame, the position coordinates of the Earth 10 years ago are exactly the same as the position coordinates of the Earth today--why is that frame any less valid than any other?DrChinese said:I am not arguing the validity of relativity, and I think you are reversing my meaning. If someone went back in time 10 years, without traversing space, they would end up far away from Earth. If they went back 1000 years, they would be even farther away.
Why "probably"? The question is just undefined, since there is no "natural" place that the laws of physics say you should expect to end up. The whole idea of instantaneously disappearing from one point in spacetime and reappearing in another has no basis in any known theory of physics--instead, physicists who speculate about the real possibility of time travel are thinking of something more like a wormhole, where you travel continuously through a weirdly-curved region of spacetime and end up inside your past light cone.DrChinese said:So as I said, if you traveled to the past, where would you go back to? Empty space probably.
JesseM said:In your paper you write: Who are these "some" who believe that the merging of black holes would be the basis for time travel? I have never heard any physicists suggesting such a thing, only John Titor's technobabble. What studies? Is the institute in Rhode Island Brown University (where I went to college, coincidentally)? Note that physicists had suggested the possibility of micro-black holes being created in supercollider collisions well before John Titor posted his story, he was no doubt cribbing the idea from something he had read.
chroot said:loz,
You have absolutely no idea what you're talking about. Let me welcome you by pointing out that personal theories are not welcome here. Virtually everything you've said is either gibberish, or simply wrong. Warning issued.
- Warren
Starship said:Relativity does not allow time travel. In fact, relativity does not allow motion in spacetime.
selfAdjoint said:Welll then call it a closed timelike curve worldline.
Starship said:Once we postulate the physical existence of a time axis, motion immediately becomes an impossibility.
http://arxiv.org/PS_cache/gr-qc/pdf/0503/0503097.pdf
selfAdjoint said:That paper has been rebutted by a famous physicist who knows its author well: http://www.arxiv.org/abs/gr-qc/0504039
False. Pretty much all physicists acknowledge that general relativity in its present form allows for time travel, although most think this possibility will be eliminated by a theory of quantum gravity.Starship said:By far the majority of physicists consider time travel as pseudoscience. There just isn't any experimental evidence that it happens.
False again. In relativity it's best not to think about "motion" at all, but just to think of "worldlines" frozen in 4D spacetime. And general relativity does allow worldlines which curve back and end up in the past light cone of some previous point on the worldine, or even worldlines which look like loops, known as "closed timelike curves". You might check out the book Black Holes and Time Warps by Kip Thorne (a well-known name in the field of general relativity, who often makes friendly bets with Stephen Hawking about various unresolved questions) for more details on this.Starship said:Relativity does not allow motion is space-time. It allows motion in space. Time is just the abstract inverse of change. Change (or motion) is primary, time is something we deduce from it.
JesseM said:False. Pretty much all physicists acknowledge that general relativity in its present form allows for time travel, although most think this possibility will be eliminated by a theory of quantum gravity.
"Few physicists know relativity"? Along with quantum physics, it's one of the cornerstones of 20th-century physics! General relativity is the framework used to understand the big bang and black holes and gravitational lensing, for example. And yes, it does allow for time travel, that's exactly what I've been saying. Like I said, you can read details in Kip Thorne's Black Holes and Time Warps, or on some of the webpages I posted earlier in this thread (post #9).Starship said:Few physicists know relativity and AFAIK relativity does not allow for time travel.
I didn't say anything about motion in spacetime. Here's an analogy I used on this thread:Starship said:Motion in space-time is itself impossible (by definition).
Think of a block of solid ice with various 1-dimensional strings embedded in it--if you cross-section this block, you will see a collection of 0-dimensional points (the strings in cross-section) arranged in various positions on a 2-dimensional surface, and if you take pictures of successive cross-sections and arrange them into a movie, you will see the points moving around continuously relative to one another (in terms of this metaphor, the idea that there is no single universal present means you have a choice of what angle to slice the ice when you make your series of cross-sections). You shouldn't think of time travel as the points returning to precisely the same configuration they had been in at an earlier frame of the movie; instead, you should just imagine one of the strings curving around into a loop within the 3-dimensional block, what in general relativity is known as a "closed timelike curve".
JesseM said:Few physicists know relativity"? Along with quantum physics, it's one of the cornerstones of 20th-century physics! General relativity is the framework used to understand the big bang and black holes and gravitational lensing, for example. And yes, it does allow for time travel, that's exactly what I've been saying. Like I said, you can read details in Kip Thorne's Black Holes and Time Warps, or on some of the webpages I posted earlier in this thread (post #9).
Starship said:Few physicists know the complex math of general relativity.
Tom Mattson said:Where do you get these ideas? Anyway, you are going to have to start backing up your assertions better if you want them to be tolerated here.