Questions about light

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It seems to me I need to find the bar y'all are enjoying, because I'm a bit perplexed and too sober. ;)

1) Tachyons are hypothetical only. No evidence of them has been found, but "absence of evidence isn't evidence of absence". The important thing is that they aren't in violation of Relativity, oddly enough.

2) They must always start and finish at a speed faster than light.

3) Their ftl speed is what we would, somehow, measure, not what speed it would experience. Light at c travels from A to B in 0 seconds (its own inertial frame). How would one even measure something that travels, say at 2c, but is at its destination before it left? To assume tachyons arrive at places before leaving their starting point seems unlikely, and, while at the bar, I would prefer a Titos and tonic before considering any alternative. ;)

The little I've read seems to show that they are simply traveling at a higher speed than c, and not some weird time thing.

A lightning analogy might help. We know how fast sound travels but we also know we will see the flash before the sound. The tachyons would arrive first before the photons, assuming they were from same emission. [One physicist (Berkely) tried to argue, erroneously, in his book that free will would fail if they exist.]

Regarding post #6, Dave, the tachyons very likely have no mass (but momentum like photons), so to use them to accelerate a ship, somehow, to incredible speeds is very unlikely. But in SF, you want to sound novel in any advanced science propulsion system, so it's not that bad an idea (physics aside). :)
 
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Still sober here!
There is lots to theorize about, for example does a tachyon go back to a certain date and then see time move forward? Or does a tachyon start right now and move backwards in time eventually reaching time zero? Option 1 would require our universe to suddenly add a bit of negative mass, reducing our total, which would violate conservation of mass.
For the tachyon to go back in time and then live a normal life would require a whole 'nother universe which would really violate mass conservation!
 
The math that says tachyons would create causality paradoxes also says that travel at a substantial fraction of the speed of light causes a "twin paradox". And, of course, there is the "double slit diffraction by single photons" paradox.

So, not that I am a "believer" in tachyons, but I am more of a skeptic of negative arguments that rely on "paradoxes" to disprove the existence of something.

Actually, wouldn't a large amount of slow tachyons, which have mass but interact with absolutely nothing we can detect, produce the effect of "dark matter"? Not "WIMPS" (weakly interacting massive particles) but rather "NIMPS" (never interacting massive particles)? And, even if they do interact "weakly", could the reason that we can't detect them be that we cannot understand data that does not seem to obey the causality tests?

I am not a proponent of that theory, but am willing to think "outside the box" as far as I can logically imagine.
 
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Twin paradox is simply a function of varying rate of time passage due to velocity.
Causality is in reference to the arrow of time not the rate of its passage.
Single slit diffraction pattern easily explained by wave particle duality.
 
Bill, pardon my disagreement, but the "twin paradox" is not simply a matter of relative speed changing the appearance of the rate of time passage between two observers - rather it is the calculated difference that occurs when two people start and end up in the same place at the same time, and their calculated difference in ages depends on which one was assumed to be traveling and which one was assumed to be at rest. Things don't work out the same for both assumptions, even though the theory is that it is the relative speed difference that causes the effective difference in age at the end. (Yes, I know that people have tried mathematical and philosophical explanations about how the accelerations involved would affect the outcome.)

And, the double slit paradox is not explained by the duality of wave and particle characteristic of photons, it is simply accepted as somehow being true. But, the experimental facts about when the double slit pattern looks like particles and when it looks like waves is not actually explained at all. In fact, isn't that part of the "entanglement" theory basis? Naming something is not the same as explaining it.

So, I am still of the opinion that simply pointing out paradoxes that we have not (yet?) accepted as truths does not provide positive proof that something must be impossible. We already have accepted too many apparent paradoxes to assume no others can exist. Yes, maybe some day we will be able to resolve those paradoxes with better knowledge/understanding that produces better mathematical formulas that make the processes clear enough to not seem paradoxical any more. But, that could apply to anything that currently seems to be a paradox.
 
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Yes, the twin paradox is as you stated. But there is a key difference between the two cases, one underwent acceleration and the other did not. Those are absolute differences not relative. But then what if both accelerated such that they stayed abreast of each other? No paradox there. And what if one accelerated one direction and the other an equal amount in the other direction? Then they would each have the same acceleration magnitude albeit in different directions. Note that atomic clocks have gone around the world on a jet airliner and found to be slow upon return. So we have directly measured time dilation.

Yes, wave particle duality explains the single slit experiment but then what explains wave particle duality? You got me there. But this is no more speculative than your argument so we are at a wash.
 

Catastrophe

"There never was a good war, or a bad peace."
Even IF one imaginary, non-existent, miniscule particle did maybe misbehave, would that be the end of the world? What would be the actual real world implications (if any)?

So often we see such occurrences when a single particle is imagined to (for instance) pass through an imaginary, non-existent, unproven passage in a never observed bent portion of spacetime, and, all of a sudden we have the USS Enterprise with a crew of hundreds passing through a time warp and conveying billions of interacting molecules, including surviving life forms.

The danger in giving undue credence to extrapolating the maybe, hypothetical, unproven behaviour of one photon is multiplying the baseless claims of conveying billions of atoms and molecules through hypothetical rifts in space time faster than light, reforming engineering- and living- forms to their complex and complete functionality, in the bat of an eye?

Talk about "giving an inch, and taking a mile" - this is imagining a Planck length and hypothesising a billion light years. The clutching of credibility, coloured as pseudo science. Limitless imagination may be praised in fiction, but please do not let it creep, unchecked, into real science.

Cat :)
 
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At least three issues here:
- Yes, if but one particle obeys a certain law, the laws of physics may have to be rewritten. Barring some sort of error in observation, one is as good as a million.

- The concept of a worm hole happens to be a particular solution to the equations of GR but that does not mean it is possible in reality. It could well be a "trivial" solution.

- Nothing wrong with extrapolation as long as we are aware there may be other factors come into play. Looking at far away galaxies receding and then extrapolating back in time to a singularity is a perfectly reasonable assumption. To declare the universe actually started out at some finite size requires an additional assumption thus is less likely. Neither model disproves the other, it is simply a matter of probability while we wait for more data.
 
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Catastrophe

"There never was a good war, or a bad peace."
billslugg, generally I agree with you, but "one is as good as a million" is on the way to the USS Enterprise. One in a million may be as good as a million widely distributed around space, but one in a billion, and then a trillion working in coordination and preserving life functions or engineering processes, is an entirely different matter. "Beam 'em up, Scottie".

Cat :)
 
One last thing about the twin paradox: Yes, we can run it where one twin undergoes acceleration and one does not. But, we can also do it with both twins accelerating, but at different rates or to different maximum velocities to the original inertial frame of reference. My point is that what we don't have is a formula that provides a quantitative explanation about how that acceleration can change things in a manner such that we always get the same ages when the twins get back together at zero relative velocity.

So, my conclusion is not that Special Relativity is wrong, but rather that it must be incomplete.

And that is my opinion of all theories that involve paradoxes that have been observed of calculated. So for tachyons, I think it would be possible for them to exist but not be capable of transmitting information, either because they have no effects that we can harness, or because they have no effects at all, except gravity. But, maybe, if they do go backwards in time, we simply can't design an experiment that can deal with the reversal in causality.
 
I did some reading on the Twin Paradox and its resolution has to do with the fact that the moving twin is not in an inertial frame of reference.
Well, sort of true. In reality, at least one twin needs to be accelerated to get a relative velocity difference. But, the theory (Special Relativity) does not address that. It simply calculates a change in time passage as a function of the speed difference and the amount of time at that speed difference. So, we expect that the solution to the calculated paradox involves the acceleration and deceleration, which is necessary for the "experiment", but is outside the conditions for which the theory is valid.

The problem is that we apparently do not have a theory, or at least a solution to a theory's math, that quantitatively tells us the results of the acceleration and deceleration on the total time passage difference, compared to a twin that remains at-rest for the duration of the experiment.

I have always wondered whether a proper time assessment for the twin paradox would end up showing that the twins have actually aged the same amount after one stays in-place and the other starts from that same place at relative zero speed, accelerates to near light speed, either circles around or stops, turns around and reaccelerates to go back, and then, whichever way that twin gets back to the starting point, decelerates to zero relative speed next to his stay-at-home twin. Frankly, that is what I would intuitively expect to come out to the same age. I just don't know of anybody who can calculate that result with relativistic theory as it is currently understood.
 
Regarding the apparent paradox, perhaps this explanation will help. Here

The last paragraph is interesting as it takes a Doppler approach. This is a little like the business analogy where “add-on” and “mark-up” differ. A 50% add-on to $1 is $1.50, but a 50% mark-up is $2, allowing the seller to make 50% profit. [I think this applies.]

iPhone with rib sauce. :)
 
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Catastrophe

"There never was a good war, or a bad peace."
Please pardon my lack of "knowledge" in this area. I am enquiring on behalf of those who are interested, but do not have, and cannot find, the necessary information about the assumptions involved in apparently knowing about the behaviour of two entities light years apart, lifetimes apart?

Is there any solid information, facts, or just more "possible solutions to equations?"

Just π in the sky?

Cat :)
 

Catastrophe

"There never was a good war, or a bad peace."
My problem is:
How can two parts of a "pair" of sub atomic entities be tracked when they are light years apart, or when one returns from having been light years away?

Isn't there a "bit of Heisenberg" going on here?

Cat :)
 
One last thing about the twin paradox: Yes, we can run it where one twin undergoes acceleration and one does not. But, we can also do it with both twins accelerating, but at different rates or to different maximum velocities to the original inertial frame of reference.
Yrs. It’s my understanding that the key is which party traveled away. The acceleration is only there to point to which party moved to a faster inertial frame. Besides, acceleration time can be minuscule and isn’t included in SR. [ SR can slice acceleration, however, into increments to reduce the math in GR, fwiw.]
 

Catastrophe

"There never was a good war, or a bad peace."
I am getting stuff like this:
"Nor is it paradoxical to find that distant events are correlated. After all, if I put each member of a pair of gloves in boxes, and mail them to opposite sides of the earth, I should not be surprised that by looking inside one box I can determine the handedness of the glove in the other."

This seems a far stretch from subatomic entities which we cannot see being put into boxes and posted. And how are we supposed to distinguish the "handedness" of a subatomic entity? I thought this was not possible?

Cat :)
 
I am getting stuff like this:
"Nor is it paradoxical to find that distant events are correlated. After all, if I put each member of a pair of gloves in boxes, and mail them to opposite sides of the earth, I should not be surprised that by looking inside one box I can determine the handedness of the glove in the other."

This seems a far stretch from subatomic entities which we cannot see being put into boxes and posted. And how are we supposed to distinguish the "handedness" of a subatomic entity? I thought this was not possible?

Cat :)
Cat, I think there is a direct parallel to glove "handedness" in the spin or other quantum aspects of fermions, which cannot have the same values in the same quantum state. So, if a pair of say, electrons were "entangled" so that they had opposite spins, then sent flying in opposite directions, looking at one would tell you what the other was like no matter where it had gone to.
What gets me about "entanglement" is the idea that forcing on of the pair to have a particular value will also force the other to have the corresponding value (same or opposite, depending on Fermi or Bose statistics for the particle type). It is the intentional forcing of a state in one of the pair that seems to make "spooky action at a distance" by the other somehow still maintaining the corresponding state, no matter how far away it is. If it were just finding out what state one particle is in, it would just be a random event that allows you to know which glove was in the other box. But, waving a wand over the box you have to somehow make it have a right hand glove for sure would seem to somehow make the glove in the other box have a left hand glove for sure. It has always bothered me that theorists claim this, but I have never really understood what experiment they used to actually demonstrate that.
 
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