<p>Let's look at the validity of tachyons first. Travelling faster than light, as said by userLTK, would create time travel, which would create the famous paradox, the tachyonic antitelephone. The tachyonic antitelephone is a violation of causality, and thus most likely, tachyons would not exist.</p>

<p>Now, take a look at another assumption. Wikipedia is right almost all times, but sadly, it has some wrong information. Such is with tachyons. It gives us some contradictory statements of tachyons too. It is wrong to assume that tachyons always move faster than light. A tachyon, is a particle with an imaginary number as its rest mass. This, however, does not mean it can travel faster than the speed of light, nor that there's any conflict between their existence and the special theory of relativity.</p>

<p>The main idea here is that the typical intuition we have about particles -- them being billiard ball-like objects -- just fails in the quantum world. It turns out that the correct classical limit for quantum fields in many situations is classical fields rather than point particles, and so you must solve the field equations for a field with imaginary mass and see what happens rather than just naively assume the velocity will turn out to be faster than light.</p>

<p>Leandro M. wrote on physics stack exchange, that</p>

<blockquote>
  <p>a good way to think about tachyons is to imagine hanging several
  pendulums on a clothesline, one after the other. If you disturb one of
  them, some amount of force will be transmitted from one pendulum to
  the next and you'll see a traveling disturbance on the clothesline.
  You'll be able to identify a "speed of light" for this system (which
  will really be the speed of sound in the string). Now you can make a
  "tachyon" in this system by flipping all the pendulums upside down:
  they'll be in a very unstable position, but that's precisely what a
  tachyon represents. Nevertheless, there's absolutely no way that you
  could send a signal down the clothesline faster than the "speed of
  light" in the system, even with this instability.</p>
</blockquote>

<p>This means that tachyons don't actually move faster than the speed of light, and your assumption is wrong. </p>

<p>Furthermore, StephenG wrote in a comment that tachyons essentially can't exist in a black hole.</p>

<p>user106422 wrote in the linked question on physics stack exchange that</p>

<blockquote>
  <p>in a nutshell, creating a tachyon itself would lead to some form of
  a spontaneous phase transition in which the tachyonic mode no longer
  exists. So from a rigourous QFT + GR setting, I don't think tachyons
  exist the way it is portrayed in simpler QM models. So no, tachyons
  will not escape the horizon simply because the theory will not allow
  for them to exist.</p>
</blockquote>

<p>Thus, no, even if they exist, they don't really travel faster than the speed of light, and even if they do, that can't really "travel" through a black hole. <strong>So, it is not possible to use tachyons to explore a black hole.</strong></p>

CC BY-SA 4.0
2019-03-01T20:09:27.433Z
2019-03-01T20:09:27.433Z
Max0815
<p>I read on a Wikipedia article lately that tachyons are theoretical particles which always travel at or above the speed of light. That means that when one passes us, we see two images, a blue shifted one and a red shifted one. </p>

<p>Black holes on the other hand have gravity so strong that light gets pulled in. However, I haven't heard that black holes can exert a gravitational pull that can pull and object that is travelling greater than the speed of light.</p>

<p>So now, I am wondering that if it is possible to use/make tachyons and control those tachyons, could we send them into a black hole and use them like a "echolocation" thing, except the sensors would be on the other side of where the tachyons are first produced?</p>

CC BY-SA 4.0
2019-02-28T02:05:57.413Z
Tachyons probably don't exist. No serious theory has ever claimed that they're likely. Even Feinberg, who coined the name, was pretty sure they don't exist. And if they do exist, we have no idea how to make them.
PM 2Ring
CC BY-SA 4.0
2019-02-28T03:44:22.297Z
@PM2Ring, if it exists, is what I proposed possible? Can u answer?
Max0815
CC BY-SA 4.0
2019-02-28T04:52:09.267Z
Black holes do not work this way : velocity is not the defining quality that decides if you can "escape".  Spacetime is distorted and this is what prevents "escape".  The closest answer to your question is in a [Physics SE question](https://physics.stackexchange.com/questions/274940/if-tachyons-exists-can-they-escape-event-horizon?rq=1) and essentially boils down to "tachyons can't exist inside a black hole".
StephenG - Help Ukraine
CC BY-SA 4.0
2019-02-28T07:17:36.800Z
@StephenG Yeah, the speed of light meme is probably the most confusing thing about the way black holes are presented in popular science. It creates the impression that if you could go "faster", you could escape. Except there is no "faster" since speed of light is essentially infinite from the p.o.v. of the moving observer. And even if there was, it's not the speed that's the limiting factor, it's the closed-in spacetime within a black hole, the literal lack of an escape route, that prevents the escape.
Florin Andrei
CC BY-SA 4.0
2019-02-28T10:34:36.690Z
Let me begin by saying that the question @StephenG posts provides a good answer to this question by someone smarter than me.    I would think, however, if tachyons did exist (they probably don't), and if we could use them to measure stuff, that is, they're not ghostly particles like neutrinos but they interact in a measurable way), then I see no reason why we couldn't, in theory, use tachyons to explore part of, but not the entire, inside of a black hole.   But as the other answer indicates, when models for quantum theory are worked out, tachyons break too many rules, so there's that.
userLTK
CC BY-SA 4.0
2019-02-28T21:44:51.747Z
@userLTK would you mind to answer so I can mark as correct?
Max0815
CC BY-SA 4.0
2019-02-28T23:09:34.107Z
@Max0815 I'm not comfortable making it an answer because it's too vague.   If FTL particles exist, they should be able to fly through an event horizon and out the other side at the right angle so as to avoid too much gravity in the center, but that's just linear math.   There's also real problems with that idea if you incorporate actual quantum models or field theory, so I don't consider it a real answer, just more of a "in theory yes, but only if you ignore several things" kind of answer.     You've given me an idea for another question though.
userLTK
CC BY-SA 4.0
2019-03-01T00:53:03.867Z
@userLTK could you at least provide an overview, because I hate to leave question unanswered. Also, I'm beginning to notice some sort of downvoting on all of my question I ask, so if that continues, I will report this.
Max0815
CC BY-SA 4.0
2019-03-01T04:01:39.363Z
@Max0815 I don't think you understand me.   I'm not comfortable answering it given how limited my understanding is.   In basic terms, an object that travels faster than light can escape a gravitational field inside an event horizon, and it enables other things which I don't understand well, such as, perhaps time travel, but these things are also impossible for several reasons.   I really don't want to make an answer on physics that's both probably not true and that I don't understand key details about.  I've bluffed my way through answers before but this one is too far outside my knowledge.
userLTK
<black-hole><light><speed><particles>
Possible to use tachyons to explore black hole?
Max0815
# Possible to use tachyons to explore black hole?

(Asked by: username_0 on 2019-02-28)

I read on a Wikipedia article lately that tachyons are theoretical particles which always travel at or above the speed of light. That means that when one passes us, we see two images, a blue shifted one and a red shifted one.

Black holes on the other hand have gravity so strong that light gets pulled in. However, I haven't heard that black holes can exert a gravitational pull that can pull and object that is travelling greater than the speed of light.

So now, I am wondering that if it is possible to use/make tachyons and control those tachyons, could we send them into a black hole and use them like a "echolocation" thing, except the sensors would be on the other side of where the tachyons are first produced?

**Tags:** black-hole, light, speed, particles
> **Comments:**
> **username_1**: Tachyons probably don't exist. No serious theory has ever claimed that they're likely. Even Feinberg, who coined the name, was pretty sure they don't exist. And if they do exist, we have no idea how to make them.  
> **username_0**: @PM2Ring, if it exists, is what I proposed possible? Can u answer?  
> **username_2**: Black holes do not work this way : velocity is not the defining quality that decides if you can "escape".  Spacetime is distorted and this is what prevents "escape".  The closest answer to your question is in a [Physics SE question](https://physics.stackexchange.com/questions/274940/if-tachyons-exists-can-they-escape-event-horizon?rq=1) and essentially boils down to "tachyons can't exist inside a black hole".  
> **username_3**: @StephenG Yeah, the speed of light meme is probably the most confusing thing about the way black holes are presented in popular science. It creates the impression that if you could go "faster", you could escape. Except there is no "faster" since speed of light is essentially infinite from the p.o.v. of the moving observer. And even if there was, it's not the speed that's the limiting factor, it's the closed-in spacetime within a black hole, the literal lack of an escape route, that prevents the escape.  
> **username_4**: Let me begin by saying that the question @StephenG posts provides a good answer to this question by someone smarter than me.    I would think, however, if tachyons did exist (they probably don't), and if we could use them to measure stuff, that is, they're not ghostly particles like neutrinos but they interact in a measurable way), then I see no reason why we couldn't, in theory, use tachyons to explore part of, but not the entire, inside of a black hole.   But as the other answer indicates, when models for quantum theory are worked out, tachyons break too many rules, so there's that.  
> **username_0**: @userLTK would you mind to answer so I can mark as correct?  
> **username_4**: @Max0815 I'm not comfortable making it an answer because it's too vague.   If FTL particles exist, they should be able to fly through an event horizon and out the other side at the right angle so as to avoid too much gravity in the center, but that's just linear math.   There's also real problems with that idea if you incorporate actual quantum models or field theory, so I don't consider it a real answer, just more of a "in theory yes, but only if you ignore several things" kind of answer.     You've given me an idea for another question though.  
> **username_0**: @userLTK could you at least provide an overview, because I hate to leave question unanswered. Also, I'm beginning to notice some sort of downvoting on all of my question I ask, so if that continues, I will report this.  
> **username_4**: @Max0815 I don't think you understand me.   I'm not comfortable answering it given how limited my understanding is.   In basic terms, an object that travels faster than light can escape a gravitational field inside an event horizon, and it enables other things which I don't understand well, such as, perhaps time travel, but these things are also impossible for several reasons.   I really don't want to make an answer on physics that's both probably not true and that I don't understand key details about.  I've bluffed my way through answers before but this one is too far outside my knowledge.  

---

## 1 answers

### Answer by username_0 on 2019-03-01. Score: 1 | Accepted answer

Let's look at the validity of tachyons first. Travelling faster than light, as said by userLTK, would create time travel, which would create the famous paradox, the tachyonic antitelephone. The tachyonic antitelephone is a violation of causality, and thus most likely, tachyons would not exist.

Now, take a look at another assumption. Wikipedia is right almost all times, but sadly, it has some wrong information. Such is with tachyons. It gives us some contradictory statements of tachyons too. It is wrong to assume that tachyons always move faster than light. A tachyon, is a particle with an imaginary number as its rest mass. This, however, does not mean it can travel faster than the speed of light, nor that there's any conflict between their existence and the special theory of relativity.

The main idea here is that the typical intuition we have about particles -- them being billiard ball-like objects -- just fails in the quantum world. It turns out that the correct classical limit for quantum fields in many situations is classical fields rather than point particles, and so you must solve the field equations for a field with imaginary mass and see what happens rather than just naively assume the velocity will turn out to be faster than light.

Leandro M. wrote on physics stack exchange, that

> a good way to think about tachyons is to imagine hanging several
> pendulums on a clothesline, one after the other. If you disturb one of
> them, some amount of force will be transmitted from one pendulum to
> the next and you'll see a traveling disturbance on the clothesline.
> You'll be able to identify a "speed of light" for this system (which
> will really be the speed of sound in the string). Now you can make a
> "tachyon" in this system by flipping all the pendulums upside down:
> they'll be in a very unstable position, but that's precisely what a
> tachyon represents. Nevertheless, there's absolutely no way that you
> could send a signal down the clothesline faster than the "speed of
> light" in the system, even with this instability.

This means that tachyons don't actually move faster than the speed of light, and your assumption is wrong.

Furthermore, StephenG wrote in a comment that tachyons essentially can't exist in a black hole.

user106422 wrote in the linked question on physics stack exchange that

> in a nutshell, creating a tachyon itself would lead to some form of
> a spontaneous phase transition in which the tachyonic mode no longer
> exists. So from a rigourous QFT + GR setting, I don't think tachyons
> exist the way it is portrayed in simpler QM models. So no, tachyons
> will not escape the horizon simply because the theory will not allow
> for them to exist.

Thus, no, even if they exist, they don't really travel faster than the speed of light, and even if they do, that can't really "travel" through a black hole. **So, it is not possible to use tachyons to explore a black hole.**


---

