Does My Wrist Watch Physically Beat Slower?

PeterDonis

Yes. So what? If tachyons are allowed, then there are still going to be causally connected events that are spacelike separated. It doesn't matter that not *all* causally connected events are spacelike separated; having *any* of them be so is enough.

If tachyons can't affect objects that aren't tachyons, and vice versa, then tachyons effectively don't exist; there's no way to detect them and no way to affect them, because we and all of our scientific instruments aren't made of tachyons, we're made of ordinary matter. There's no point in discussing tachyons if they can't interact with ordinary matter; we can simply ignore them.

Tomahoc

Even without tachyons there are some problems with inconsistency. Going to the train example and 2 lightnings hitting both ends. It is said in:

http://www.rafimoor.com/english/SRE.htm

"Suppose we put two photoelectric cells at point P on the train where the two flashes of light meet in the man’s frame. One of the cells is directed to the front of the train and the other to the back. Now we connect the cells to a bomb in a way that if the two cells are illuminated simultaneously the bomb explodes. In the man’s frame the bomb will explode. In the woman’s it will not since in her frame the flashes meet by her and not at point P."

The woman is the one sitting on the moving, the man on the station at point P. The website didn't answer if the woman is dead or not. So do you think it explodes? The website didn't give details of what happen at the end. Just look at the illustration as the lightning and train example is classic. So there are some frames it explodes and some frames it doesn't? If not.. does it explode or not?

DaleSpam

No, there are no problems with inconsistency, and there are no disagreements between frames on whether or not it explodes.

Similar problems are often given as homework in introductory relativity classes.

PeterDonis

The word "simultaneously" is being used here in a different sense than you are interpreting it; it does not refer to two spacelike separated events, but to a single event--a single point in spacetime--at which two things happen (each cell receives a flash). A better way of phrasing how the cells are connected would be: "if the two cells receive light beams at the same spacetime event, the bomb explodes". That phrasing makes it clear that whether or not the bomb explodes is frame-invariant. See further comments below.

No, this is not correct. The two flashes do *not* meet by the woman; the woman sees the flash from in front of her *before* she sees the flash from behind her. The two flashes meet at point P even in the woman's frame; the difference is that in the woman's frame, point P is moving, whereas in the man's frame, point P is at rest.

It explodes.

Tomahoc

Not so fast. Prior to the paragraph. It is said that "That is, while the man measures the light from the front getting to the woman before the light from the back, the woman sees the light from both sides simultaneously.".

The web site especially mentioned that the woman sees the light from both sides simultaneously. So dead or alive, that is the question.

PeterDonis

Please read more carefully. The statement in quotes is a *hypothetical*, which the author later shows to be false. He is *not* stating it as an actual conclusion of relativity.

[Edit: The same is true of the statement I said was incorrect: "in the woman's frame it will not since in her frame the flashes meet by her and not at point P"--it is also part of the hypothetical, which the author later shows to be false.]

Tomahoc

Ok. I'll look into them. For now. I'm looking for web sites that illustrates what you mentioned that "If tachyons are allowed, then there are still going to be causally connected events that are spacelike separated. It doesn't matter that not *all* causally connected events are spacelike separated; having *any* of them be so is enough.".

Know any such web site with spacetime diagrams of tachyons and effects on causality to get me busy this weekend.

Or maybe an actual example you already knew. If the baseball is made up of normal matter and throws into a windows. If no tachyons, there is no frames where the order is reverse? If there are tachyons flying alongside.. how come it can be reverse? I get the essence, but want exact details of how the worldline details work that can make the ordering reverse or chaotic. Thanks.

PeterDonis

This follows from the definition of tachyons: they travel faster than light. That means they travel on spacelike worldlines, so successive events on a tachyon's worldline are spacelike separated.

If the baseball is made of normal matter, then it travels on a timelike worldline. The time ordering of events on a timelike worldline is frame invariant. (The same is true of the ordering of events on a lightlike worldline, so a "baseball" made of photons would be the same in this respect as a baseball made of normal matter.)

Please read carefully. I didn't say "a baseball with tachyons flying alongside it"; I said "a baseball *made of* tachyons". That means the baseball itself is moving faster than light.

See above. The time ordering of events on a spacelike curve is frame-dependent. That's just a basic fact about spacelike curves.

Tomahoc

Ah. As long as closed causal loop is solved by tachyons moving fixed in aether frame. There is no problem about reverse order. I mean. When you rewind your video tape or fast forward them. It is just in the function. One knows that window doesn't spontaneously reassemble. So if a frame shows that. We can say "Ah, it's just an artifact"... unless you want to argue that what happens in a frame actually happens such that the window spontaneously reassemble? But then we can just say to ignore it... and just treat the normal ordering as actual with the reverse order virtual like virtual particles.. just an artifact effect.

DaleSpam

Good, I am glad that you agree with that much at least.

Honestly, I don't place any significance on LET, it is merely the most well-known counter example to the Vandam's false claim that the experimental evidence we have to date can only be interpreted as a block universe and not as any other interpretation as well as his other false claim that the relativity of simultaneity implies a block universe.

Lorentz's disavowal of LET is historical trivia and not relevant to the question of whether or not the evidence supports it. Science isn't a popularity contest, the only vote that counts is nature's.

If you wish to continue the search then this is where you need to focus your efforts. The task is fairly clear: find an experiment where LET predicts X and block-universe predicts Y with X≠Y. I don't believe the task is possible, for the reasons stated above, but at least it is clear.

What you can say that is not overstepping is that the evidence is consistent with a 4D universe. You can also talk about the many aesthetic, practical, and philosophical advantages of the block-universe approach over other approaches, like LET. If you don't claim that the block universe is the only interpretation supported by the evidence then your drawings and explanations would be quite beneficial, I think. And there is certainly nothing wrong with simply stating that it is your clear personal preference.

PeterDonis

But how do we know that? Because we always see the events in the same order: throw baseball, then window breaks. If baseballs made of tachyons were commonly observed, and we commonly saw the events in the opposite order, we might not be so confident that we knew which order was the "right" one.

Part of the standard physical interpretation of a frame is that "what happens in a frame actually happens", yes. There is no room in the standard interpretation for some observations made in a frame to be "artifacts".

Since you mention virtual particles, it's worth bringing up the point that if we include quantum mechanics, we can no longer say that tachyons can actually transmit information or causal influences faster than light. See here:

http://math.ucr.edu/home/baez/physic.../tachyons.html

The same is actually true of virtual particles: virtual particles in quantum field theory can travel faster than light, but they can't be used to transmit information or causal influences faster than light, for the same sorts of reasons as tachyons can't be used that way as explained in the article above.

jk22

I think there are experiments checking the constancy of the speed of light no matter what the motion of the observer is in the so called emission theory (see Wikipedia), for example by measuring the speed of sun light during spring and autumn or from binary star systems and no significant difference could be found.
Another way to test it is the Sagnac interferometer that uses rotating mirrors.