[petelamana (OP)]

Lately I have been reading posts from some years ago.  I realize that the information in some of these posts can still be considered "on-point", while other information wouldn't know the point if it stabbed them.  To that end, would someone please bring me up-to-date on the info from the following post...

Re: What are tachyons?
« Reply #6 on: April 06, 2009, 05:07:30 pm »

Vern's post:

It is entangled photons that seem to pass information at faster than light speeds. When the polarization of one of a pair of photons is changed, the other of the pair seems to instantly take on that polarization. I suspect that there's another mechanism at work, but don't have a clue about what it might be.

I don't think there's a theory that suggests that tachyons actually exist. There is a body of work that fits them into the Quantum Mechanical realm, but it only suggests that if they existed, they would have certain properties.

I think the closest we can come to observing them is in media such as water when an electron can exceed light speed in that medium.

I will save the multitude of questions I have until later.

Thank you.

[Bill S]

I’m certainly no expert, but here are some thoughts about the tachyon, just to set the ball rolling.

The tachyon is a theoretical particle that always travels faster than light.  It is never accelerated from subluminal to superluminal speed, so it doesn’t contravene the rules of SR, but it does travel backwards through time, relative to us, which raises some interesting thoughts.

You may have seen the quote from John Gribbin at:

https://www.thenakedscientists.com/forum/index.php?topic=72229.0

“So if a tachyon were created in some violent event in space, it would radiate energy away furiously…..and go faster and faster, until it had zero energy ……and was travelling at infinite speed”.

To detect a tachyon, one would have to look for an event, the cause of which had not yet happened.

The prospect of looking for something that may be travelling at infinite speed, may be undetectable and, in any case, has not been formed yet, does seem to be quite a daunting task. 

[petelamana (OP)]

To detect a tachyon, one would have to look for an event, the cause of which had not yet happened.

The prospect of looking for something that may be travelling at infinite speed, may be undetectable and, in any case, has not been formed yet, does seem to be quite a daunting task.

And perhaps something best left to the creativity of science fiction.  However, like much fiction, science or otherwise, there is almost always an underlying bit of reality.

[jeffreyH]

You ask what is the truth about the subjects of your title. Are you trying to determine which information may contain misconceptions?

[Colin2B]

tachyon ...it does travel backwards through time, relative to us, which raises some interesting thoughts.   

For some observers, not all. You need to be clear who ‘us’ are.

[jeffreyH]

If the observer is Dr Who then he beats tachyons hands down.

[Colin2B]

If the observer is Dr Who then he beats tachyons hands down.

Oh, I see, they are some sort of dalek?

[jeffreyH]

Shame on you. Now you are just speculating wildly. That is no example to set.

[Bill S]

For some observers, not all. You need to be clear who ‘us’ are.

"Us" would be the occupants of our "observable" Universe.  So, who are the observers who would see the tachyons travelling forward in time?

I don't believe I've just written "Us would be" 

[jeffreyH]

Just because mathematics may contain a negative time element does not necessarily indicate physical particles traveling back in time.

[evan_au]

entangled photons ... tachyons

These are quite different concepts, and unrelated (as far as I know).
- Tachyons are hypothetical particles that only travel faster than light
- Photons are real particles which always travel at the speed of light in a vacuum
- Entangled photons have been demonstrated in the laboratory, but cannot be used to transmit information faster than the speed of light (as far as we know)
- Other types of particles can also be entangled (eg electrons)

when an electron can exceed light speed in that medium

This is a real effect, seen in the blue glow around a nuclear reactor.

See: https://en.wikipedia.org/wiki/Cherenkov_radiation

quantum mechanics?

Quantum mechanics is a well-proven technique applied to photons, electrons, atoms and molecules.
https://en.wikipedia.org/wiki/Quantum_mechanics

The Standard Model extends this to all known subatomic particles and has been quite solid since the presumed Higgs Boson was confirmed.
https://en.wikipedia.org/wiki/Standard_Model

There are experiments underway at the LHC to see if the Standard Model can be extended to new particles (eg super-symmetric partners to known particles), but there is no solid evidence for these hypothetical extensions at this point in time.

baryonic string theory

String Theory at present is only a hypothesis, which  has so far been quite unsuccessful at describing subatomic particles. This is apart from the graviton, where it has done ok - but not really any better than General Relativity (which is not a quantum theory at all).
See: https://en.wikipedia.org/wiki/String_theory

[Colin2B]

"Us" would be the occupants of our "observable" Universe.  So, who are the observers who would see the tachyons travelling forward in time?

I don't believe I've just written "Us would be" 

Well, the us would be occupants of our observable universe of course 
The problem is deciding which ones.
Each occupant will measure a different passage of time in other reference frames due to relative motion. We know that the concept of simultaneous is a problem when you start moving relative to another frame even with sub light speeds, and there are situations where an observer can measure apparent backwards motion in other frames which are moving at super light speed.

 

Just because mathematics may contain a negative time element does not necessarily indicate physical particles traveling back in time.

Wise words.
Some equations return more than one value + & -. In some equations it is possible to view negative energy moving backwards as positive energy moving forwards, so common sense can prevail - until proven otherwise?

Shame on you. Now you are just speculating wildly. That is no example to set.

Why should i be any different to everyone else?

[Bill S]

….there are situations where an observer can measure apparent backwards motion in other frames which are moving at super light speed.

Interest definitely piqued, here.  Is this just in principle/theory?  The only “physical” example of superluminal speed I can think of is the motion of galaxies in the process of expansion; and we can’t actually observe that.  What am I missing?

[Bill S]

Just because mathematics may contain a negative time element does not necessarily indicate physical particles traveling back in time.

My Hero! 

BTW, not everyone knows this, but the real reason the Daleks  failed to conquer Earth was that they couldn't cope with stairs.

[Colin2B]

What am I missing?

Not a lot.
We were talking tachyons. Because they travel faster than light their paths are in the part of the Minkowski diagram where events are spacelike, where observers cannot agree on the time order of events (unlike the timelike area where observers do agree on the time order). It also means that events in that area are not part of your absolute future. So one observer might see A happen before B, but another observer would disagree.
It’s all relative