Tachyons and tachyon guns

Alright, I’ve got another noodle scratcher (possibly for the guys who helped me with the whole neutron bomb situation).

Recently I was talking to my brother (Age 20), who was talking to me about Einstein’s theory of relativity, and how some people think they’ve discovered that it’s wrong (that will be in my next thread if I don’t find out more on my own). Anyway, my brother said that there’s a theoretical particle of some sort called a tachyon (I’m not sure if I spelled it right) that goes faster than the speed of light. He went on to say that if a tachyon gun were to be invented, the object you were shooting at would be dead before you pulled the trigger, or something to that effect. He also said that tachyons are thought to speed up as they lose energy, and could travel back and forth across the universe in a second. Now, my brother didn’t seem to know to many details, so I have to ask the brilliant Straight Dope community. How can this be? Do you know ANYTHING about tachyons? It really interests me thank you!:rolleyes:

Briefly, from a George Sudarshan page:

When I had Dr. Sudarshan as my physics professor back in the 1970s, the buzz was that he’d be a shoo-in for a Nobel Prize if anybody could make any headway on detecting evidence of the existence of tachyons. I haven’t seen that much has happened on that front.

2 things here - First the tachyon is, like you say, theoretical. Just because it could exist, doesn’t mean it does exist. Second, as far as dying before you pull the trigger - no. Just because a theoretical particle may exist doesn’t mean that the concept of cause and effect has been repealed.

Stadard IANAP disclaimer.

… Gave me details and extra things that my brother couldn’t tell me about. Thanks guys. :smiley:

I didn’t think tachyons could theoretically interact with normal particles. I could be completely wrong about that, however, anybody know?

Tachyons move faster than light. That doesn’t mean they arrive at the target before they leave the source, just that they arrive before anything else could.

On the other hand, all other sources of information about what is happening, and all other mechanisms for cause and effect are limited by the speed of light, so you will perceive some really weird phenomona.

It’s all about frame of reference. In Special Relativity, simultaneity is relative. If something moves faster than light in one frame of reference, it will move infinitely fast in some other frames, and backwards in time in some other ones.

If you were to watch the arrival of an object moving faster than light, you could not see it until it had arrived. Then the light would catch up and it would look like it was leaving.

It’s not clear from your post, but tachyons don’t contradict relativity - while the popular version is ‘you can’t go faster than light’, you could more accurately put that part as ‘you can’t accelerate to or past the speed of light, or decellerate to or below the speed of light’. Faster than light communications can cause problems with casualty, though a ‘tachyon gun’ wouldn’t act like you describe (to get the ‘person dies before you pull the trigger’, you’d need an observer moving around at some speed IIRC).

The problem with a tachyon gun is that tachyons theoretically would not be able to interact with normal matter; they couldn’t be bound into place to transmit information or energy. It’s been a good while since I’ve read up on it so I don’t have a good explanation or source, but I suspect one of the more physics minded dopers could tell you where to look for information.

This info is great!

Do any of you who have researched tachyons know of any good books on the subject? I’d like to know more, thank you again.

I think the proper frame of reference for the “death before firing” effect would be that of the target, or a bystander near the victim. If the projectile moves FTL, and death is “instantaneous”, then the tachyon-bullet would arrive between the subject’s eyes before the light that bounced off the killer’s moving trigger finger reached the now-dead guy’s pupils.

As reliable as he is;), I was talking to my dad, and he said he had learned something about tachyon rays back in the day. He said he learned something about tachyon devices such as guns, if they were ever created, they would shoot, or activate before the thought to activate or pull the trigger even occurs. I don’t think it’s possible, but what can you guys tell me?

<VIBRO raises his hand>

You! In the back! Vibrating guy!

Um…Pardon my ignorance, but can you clarify your statement about how an object moving faster than light would appear to be leaving when it’s actually arriving? I don’t understand how that could be so, and if it is so, wouldn’t it mean that we can’t ever know if an object is moving forward at a speed <c or backward at a speed >c?

Actually, the problem would be greater than you raise – since tachyons would move backward in time, the problem with a tachyon gun would be that any time you saw something dead, you would have to aim the gun at it, so that the tachyon which killed it could move from it back to the gun.

Does FTL automatically assume moving backwards through time? Or does that depend on the observer?

I understand the concept of time dilation, but does time actually backup for someone moving FTL or does it just stop?

tachyon gun cant work because you cant make a round to hold said tachyons. however is it theoretically possible to make a “gun” that generated a collective of tachyons preferably bullet sized and ejected it out the barrel. i don’t know just an idea

I didn’t get it either at first, but after thinking it out, I believe it would work the following way :

1)The bullet arrives, but moving faster than light and all, you see nothing while being wounded

2)An instant later, the light emitted when the bullet was just in front of you arrives, so you see the bullet where it was before hitting you, say 10 centimeters away.

  1. An instant later, the light emitted a bit earlier, when the bullet was 1 meter away from you arrives, so you see the bullet 1 meter away

4)And so on…so the bullet appears to be moving backward. Eventually, you’ll see the gun firing and the bullet leaving it.

Please correct me if I’m wrong.

Quoth caveman:

Location isn’t relevant, only velocity. It’s not just a matter of “dead before you see the shooter’s trigger finger move”, it’d be “dead before the trigger finger moves at all”. Or at least, it would be, if it were possible to make a tachyon gun or to die from a tachyon bullet, which it isn’t.

please explain why it isn’t theoretically possible to create a weapon that generated a collective of tachyons, and why you could not die from said collective

Could a tachyon gun shoot this thread when it was first posted in 2002?

I gather from previous responses that tachyons, if they exist, can’t interact with normal matter.