[Aardwolf]

Tachyons are, as I understand it, hypothetical particles which travel faster than light.

Somehow, such a particle would have to have imaginary mass (I haven't find the source for that, but I saw it somewhere and I'm sure it should be fairly easy to locate).

So, what would something with imaginary mass do were it to collide with a particle with positive mass?

Feel free to discuss this and other things related to tachyons (in science, preferably, and not as used in science fiction).

[FUBAR-BDHR]

I thought that they were originally theorized because there was loss of mass during an experiment.  Basically since E=MC^2 wasn't preserved they knew there had to be a partial that disappeared somehow.  FTL or time travel were possibilities.   

[Aardwolf]

I don't know about that really, but it sounds like it could have been explained by neutrinos instead.

[Herra Tohtori]

I thought that they were originally theorized because there was loss of mass during an experiment.  Basically since E=MC^2 wasn't preserved they knew there had to be a partial that disappeared somehow.  FTL or time travel were possibilities.   

Yeah that is how the existence of neutrinos was hypothetized and eventually proved to actually be the correct expectation.

Tachyons are a lot more hypothetical. Basically, they are based on the interpretation of relativity that essentially says that objects with a rest mass always travel at sub-light speeds in relation to others, objects with no rest mass will always be measured as traveling at light speed (which is the reason why light speed is constant and co-ordinate-independent), and objects iwht imaginary (or negative mass, depending on how one is to interpret mathematical strangeness like imaginary mass to reality) would always travel at superluminal speeds in relation to objects with rest mass.

Tachyons are the name given to these hypothetical particles. What makes them both interesting and dull is that if one is to assume that light speed is the speed of causality, tachyons cannot be used for information transmitting purposes because that would break the causality; you would have the effect before the cause.

Of course, one could argue that it wouldn't mean causality breaking, but instead it would just mean that light speed wouldn't be the highest information transmission speed in the universe.

If tachyons were to interact with particles that have rest mass, situation would be pretty interesting. Because tachyons basically would have negative mass (mathematically it would be imaginary mass, but the interpretation of equations to reality would pretty much mean that the mass is negative... at least to my understanding), their momentum vector would actually point to the direction they came from. Which is kinda interesting because if one were to assume that objects with mass would continuously emit tachyons, it would result in a force that would draw the objects with mass closer to each other... Of course we would notice if such a force were to exist in universe. Oh wait, there is such a force. Silly me...

Note that this is just a thought experiment and is not a serious attempt to explain gravity as mass-tachyon-interactions. To do that, one would need to determine that the velocity of gravitational propagations is greater than light speed, AND find a mechanism that would explain why objects with mass would emit tachyons continuously, AND explain why and how exactly tachyons interact with particles that have mass.

Determining the velocity of gravitation has historically been quite difficult and results are as of yet inconclusive; in general relativity, the changes in the "tilt" of space-time fabric propagate at light speed as far as I know, but that's just one interpretation of theory and doesn't mean that reality is obliged to follow the model. Although the great accuracy of general realtivity gravitational model does suggest that either it's a very good approximation/abstraction of what's going on, or it actually corresponds to reality (within definite error bars).

Personally, I'm very eagerly expecting conclusive reports from LHC on whether the Higgs' boson exists or not...

[FUBAR-BDHR]

There's been something bothering me about this whole can't go faster then the speed of light law.  Isn't light made up of waves?  If so aren't  the photons or whatever the waves are composed of already exceeding the speed of light?  If say a laser beam is going in a straight line the beam is moving at the speed of light.  The waves that make up that been would have to be traveling faster since they have to cover a greater distance in the same time.

[Herra Tohtori]

There's been something bothering me about this whole can't go faster then the speed of light law.  Isn't light made up of waves?  If so aren't  the photons or whatever the waves are composed of already exceeding the speed of light?  If say a laser beam is going in a straight line the beam is moving at the speed of light.  The waves that make up that been would have to be traveling faster since they have to cover a greater distance in the same time.

Wave motion doesn't really work like that. If you look at a photon as electromagnetic wave motion, you need to consider the elctric fields and the magnetic fields in vacuum kinda like the surface of water, where a wave propagates. The photon propagating through vacuum simply first changes the electric field to one direction and then to other while doign the same to the magnetic field, and then it's gone from that part of the vacuum. They themselves don't move anywhere, it's just the change in the zero potential of vacuum that travels along with the photon... or, depending of interpretation, forms the photon.

Also, phase velocity can exceed the speed of light in some conditions, but information velocity (distance from emission to absorption divided by the time used on it) of the photon (also sometimes called group velocity) itself cannot be greater than c.

Besides, the fact that behaviour of light can be modeled as electromagnetic wave motion doesn't mean that it is merely wave motion, because every particle can be modeled as wave motion; it's just that photons' deBroglie wavelength is the same as the wavelength of the electromagnetic wave. It's possible that it is merely electromagnetic wave motion, but just as well in some cases the behaviour of photons can be described with a particle model. The duality of photons is just much more pronounced than the duality of particles with rest mass.

For example, electron microscopes are based on the fact that electrons can have way shorter wavelength than photons - or rather, photons with low enough wavelength would just pass through or fry the sample. Shorter wavelength makes it possible to get better resolution, obviously, which is why electron microscopes are so much more useful than light microscopes when it comes to really small stuff.

[Bobboau]

There's been something bothering me about this whole can't go faster then the speed of light law.  Isn't light made up of waves?  If so aren't  the photons or whatever the waves are composed of already exceeding the speed of light?  If say a laser beam is going in a straight line the beam is moving at the speed of light.  The waves that make up that been would have to be traveling faster since they have to cover a greater distance in the same time.

short answer,

no.

[Goober5000]

...one would need to determine that the velocity of gravitational propagations is greater than light speed...

Hasn't there already been work in that direction?  I remember reading once (I forget where) that somebody posited that gravity should propagate at many times light speed.  Otherwise, planetary orbits would experience lagged feedback and become chaotic.

[Aardwolf]

No, gravity has been measured to propagate somewhere between .8 and 1.2 x c, (source is probably wikipedia).

I'd never thought about that, but it seems to work fine for us, and I'm pretty sure gravity propagation should be exactly c.

[Al Tarket]

i can imagine you guys and girls chatting away to so many very intelligent scientists along with Samantha carter and then jack O'Neill comes in wonders what the hell is being said puts his hand up and says "AAAhh! oh no" looks around and walks out .

ftl hasn't been proven and words won't change that, making this whole discussion void. imo of course.

[Aardwolf]

lolwut?

This is a discussion about the hypothetical particle called the tachyon. We're not trying to "prove ftl" (how do you prove "faster than light" anyway, it's not something that can be proven or disproven... it's just a term used to describe any hypothetical (keyword: hypothetical) means of travel or communication that reaches its destination before light would.) And your Stargate reference makes no sense and has no place here anyway.

Whatever.

[Al Tarket]

hey, i have much as right as you do to ask and put my opinion across. i do not need you telling me how to run my life thank you. whatever, the same to you.

if you just explained the hypothetical thing a bit clearer i would of made a better remark, unless you think that is out of order as well?


lolwut???.. whatever you said... or whatever it means.

[General Battuta]

No, gravity has been measured to propagate somewhere between .8 and 1.2 x c, (source is probably wikipedia).

I'd never thought about that, but it seems to work fine for us, and I'm pretty sure gravity propagation should be exactly c.

Gravity should propagate at exactly C, I believe. Though I'd have to do some research to figure out what elements of the standard model support that (relativity seems pretty clear on the point.)

[Herra Tohtori]

"Should" and "does" don't always coincide...

I would expect space-time changes to propagate at light speed, though. That is, assuming the model of general relativity actually is a description of reality. However measuring this is difficult because apart from tidal forces it's rather hard to detect gravitational waves; defining their direction and velocity would be even more difficult though not impossible. The gravitation waves inducing tidal forces have way too long a wavelength and amplitude (thankfully) for us to define what velocity it's propagating at.


The only reason I brought up gravity was because tachyon-mass interactions would look like gaining "negative" momentum, or in other words, particles would start moving towards the direction of tachyon source. That is, if mass and tachyons can interact, and if my interpretation of imaginary mass = negative mass is correct. Adding an assumption that every object with invariant mass does actualyl emit tachyons, and you get a rudimentary model of gravity.

The obvious weakness in this model are plenty, mainly it's reliance to multiple assumptions that are pretty much unfalsifiable as of now. Like the fact that tachyons are completely hypothetical to begin with... Still, the idea of mass/tachyon interactions is pretty interesting.

[Mika]

About wave and particle-like duality: these are two things that should never be attempted to be used at the same time. It doesn't work that way. You either choose one to model that what you do.

Of course, QED states photons are particle -like - which poindexters with large particle accelerators have found to be a good model - and averaging masses photons yields electric field and wavelike behavior  - which cannot explain what happens anything inside the atom or like - which in turn can be simplified to light rays  - which cannot explain why rays don't always move in the direction stated by the local geometry - which can then be simplified to paraxial optics, where light ray angles are limited to a couple of degrees from local optical axis...

Mika

[Goober5000]

and if my interpretation of imaginary mass = negative mass is correct.

CP should be along to slap you shortly.   Imaginary != negative.

However, the square of the mass would be negative.  Though I can't offhand think of any equations with m² in them.

[Herra Tohtori]

and if my interpretation of imaginary mass = negative mass is correct.

CP should be along to slap you shortly.   Imaginary != negative.

However, the square of the mass would be negative.  Though I can't offhand think of any equations with m² in them.

'tis a fair point, but I already explained my reasons for this interpretation earlier, and I'm the first to admit that it is a pretty big if there about the interpratation being correct:

If tachyons were to interact with particles that have rest mass, situation would be pretty interesting. Because tachyons basically would have negative mass (mathematically it would be imaginary mass, but the interpretation of equations to reality would pretty much mean that the mass is negative... at least to my understanding), their momentum vector would actually point to the direction they came from.

Since the observations made of an object hitting you at superluminal speeds would actually look like it was moving away from you after coming to contact with you, I find this actually the only sensible interpretation available, if one is to attach the term "imaginary mass" to reality in the context of our current knowledge of reality in the first place.

A tachyon passing you would be more interesting, since you would see two images of it, but if the tachyon interacts with you (ie. you stop it), you'll only see the image of the particle as if it was moving away from you after it hit you...

...In fact it would look like you actually emitted the tachyon in the first place.

[perihelion]

Something about the idea of imaginary mass just doesn't sit well with me.  Even if you can come up with some sort of conceptual understanding for what "imaginary mass" would be (and I dispute this, heartily), you've just opened a huge can of worms.  What happens when you have mass that falls somewhere in the complex realm m = a+(i*b)?  What the gibbering balderdash would that be?

Negative mass (referred to in some circles as "exotic matter") makes some amount of conceptual sense as long as you don't get too bogged down in the particle physics of it.  Imaginary mass is like adding a new axis, and dimension, to the previously scalar quantity "mass."  The Standard Model would have to be wrong on so many levels its not even funny.

[bash]

Ah, yes, tachyons. Quite interesting things, you can do a whole lot of stuff with those, I just recently stumbled upon a device that emits tachyons to "help you balance you inner energy patterns" or some crap like that.
But let's take a look at real world physics. What are tachyons really? Basically, until proven otherwise, they are one solution of Einsteins special theory of relativity. But does that mean they exist? In my opinion: NO.
I'll illustrate my point by an example of Pythagoras (yes, the triangle guy). As you all know, his famous formula for triangles is a² + b² = c², c being the hypotenuse. Now, if you solve this formula, you get not one but two solutions for the hypotenuse, c and -c. As far as math is involved, both solutions are correct. But if you try to take this solutions to real world physics, the solution -c disappears. A triangle with a negative length for the hypotenuse simply doesn't exist. It's basically the same with tachyons: they are the negative hypotenuse of your average particle.

[Mika]

While your argument does make sense and sounds compelling (for me at least), it has two weak points:

First, That works in Euclidian space Special relativity and general relativity are different, because you must add the time component in the world position vector [x y z t].

Second, Black hole is another curiosity that was completely predicted by the mathematics alone. Singularities tend to be a problem in the mathematical point of view, which is a reason a lot of Physicists didn't take that as a real phenomenom.

Mika