The Problem with Faster Than Light Particles | Tachyons Explained

Tachyons travel faster than light, so do they go backward in time? Well, maybe, but they probably don't exist. Here's why.

Watch this video ad-free on Nebula:

Nick Lucid - Host, Writer, Editor, Animator
Em Lucid - Producer
________________________________
VIDEO ANNOTATIONS/CARDS

4-Velocity:

Speed of Light:

What if YOU were made of Light?
________________________________
RELATED YOUTUBE VIDEOS

Isaac Arthur on Tachyons:

ScienceVerse on Tachyons:
________________________________
SUPPORT THE SCIENCE ASYLUM

Patreon:

YouTube Membership:

Sign-Up for Nebula:

Advanced Theoretical Physics (Paperback):

Advanced Theoretical Physics (eBook):

Merchandise:
________________________________
HUGE THANK YOU TO THESE SUPPORTERS

Asylum Counselors:
Richard Senegor

Asylum Orderlies:
Chloë Joan López, Dhruv Singhal, James Smith, Joel Wolhendler, Medec Hurtz, Peter Engrav

Einsteinium Crazies:
Benjamin Sharef, Eoin O'Sullivan, Jonathan Lima, Joseph Salomone, Kevin Flanagan, Matias Cveczilberg, Sean K, Sheila Owen, YouTubeviewer2014

Plutonium Crazies:
Al Davis, Compuart, Dan Sullivan, Ellis Hall, Fabio Manzini, Kevin MacLean, Rex_zane, Rick Myers, Vid Icarus

Platinum Crazies:
Cesar Moya, Clayton Bruckert, David Johnston, Ishay Oz, Jonathan Reel, Joshua Gallagher, Li-Ce Hu, Marino Hernandez, Mikayla Eckel Cifrese, Mr. Orn Jonasar, Olga Cooperman, P. Patrick Tukkers, Stephanie Beach, Zachary Milne
________________________________
LINKS TO COMMENTS

________________________________
TIME CODES

00:00 Intro
00:43 What is a Tachyon?
01:27 What Everyone Gets Wrong
02:28 Spacetime Basics
03:24 Velocity Angles
04:18 Infinite Speed
05:15 How to Time Travel
06:28 Spacetime Distortion
07:23 Causality isn't Broken
07:54 More Weird Stuff
08:20 Tachyons are Imaginary
08:51 Outro
09:31 Featured Comment
________________________________
Corrections:

00:56 "Lux" is actually Latin, not Greek. Oops! My bad.

[ScienceAsylum]

0:56 Oops! Apparently, "Lux" is Latin not Greek. I'm not sure how I messed that up. Kind of ruins the whole bit I was going for. Oh well 🤦‍♂

[JorgeUribe]

And the bartender said “Hey, we don’t serve faster-than-light particles in here.”
One day, a tachyon walks into a bar...

[gaelonhays]

"Math always gives us an answer, even if our question isn't about reality." -- Nick Lucid
May be one of the best math/physics quotes I've heard in a while. I don't know if he was quoting someone else, though.

[mbchrono]

"Math always gives us an answer, even if our question isn't about reality." 🔥

[marcelobiason]

That phone call at 0:30 and 7:15 is Christopher Nolan's level genius.

[quantizado]

A fact that is generally overlooked about "time move slower the faster you go", its thats only true relative to another frame of reference. The electron in question will always perceive its time passisng normally, a second will always last a second for it, but it will expercience the outside world to move way faster and distances shirinking

[feynstein]

"Bradyons" sounds like an honorific awarded to Numberphile fans 😂

[brothermine]

It's common to use the Special Relativistic equation in hyperbolic form:
c²t² - x² = c²τ²
But it makes more sense to subtract the negative term from both sides to express it in Pythagorean form:
c²t² = c²τ² + x²
Divide both sides by t² to get
c² = c²τ²/t² + x²/t²
That's more relevant when discussing "speed" through 4-dimensional spacetime, because τ/t is the traveler's _rate of aging_ from the perspective of a stationary observer and x/t is the traveler's _speed through 3-dimensional space_ from the perspective of the stationary observer. From those two terms, one can deduce the traveler's speed through 4-dimensional Minkowski spacetime, from the perspective of the stationary observer.
The c² coefficient in the c²τ²/t² term is the conversion factor between the units of time & length, for the two "speeds" (rate of aging and speed through 3-d space). Since units are arbitrary, they could be chosen so that c=1:
c² = τ²/t² + x²/t²
It's a Pythagorean equation, where the square of a right triangle's hypotenuse equals the sum of the squares of the triangle's other two sides. In this case, the hypotenuse is the speed of the traveler through 4-dimensional Minkowski spacetime. (Minkowski spacetime has its time dimension orthogonal to each spatial dimension, which means the triangle is a right triangle.) So the square root of the left side is the traveler's speed through Minkowski spacetime, and it equals c, the same as the speed of light through 3-dimensional space. (And it equals 1 in the appropriate units of time & length.) The equation works for any kind of traveler, including light, and it presumably also works for tachyons. Everything travels at speed c through Minkowski spacetime.
The equation tells us the rate of aging of a tachyon is imaginary, the square root of a negative number. But it's unclear whether aging at an imaginary rate has a physical meaning, so it might be impossible for tachyons to exist.

[sabarapitame]

"Fast, fast!" was the first thing that I thought as I read the title of the video

[Sultan_A]

Superb, The Science Asylum, Keep It Up. 🌟 Yaaaayyy!!!! 🤗 And I’m Sultan Al-Khaldi

[bigfool]

You are a good science communicator. Many people do not make the distinction between maths and reality, although maths can give the best description of what is happening or will happen, the parameters need to be correct and precise, which a lot of people fail to see.

[parallaxe]

Hello. Such a good episode Nick. This reminded me of your earlier works, the joy, the fun and the choice of topic. Thumbs up all the way.

[chuckoneill]

"Imaginary" numbers do show up in real world engineering, too.

[contessa.adella]

Thank you. Since college (40 yrs back) I pondered what happens if you could go slower than STOP! My intuitive idea was backward time travel… Nick’s closing point is key to many maths revelations. Just because some idea can squeeze an equation out of a maths anomaly doesn’t mean it exists in our reality. Mathematicians generate some incredible meta concepts, but it takes a physicist to keep them grounded……Another brain stretcher was what would we see if Pi was a different value than 3.14…. It took me years to understand that one (ans: it warps things into an extra dimension. In curved spacetime for example pi is a bit bigger making you take longer to approach a mass than the geometric distance would seem…in this case that extra dimension is time. Pi is only the well known of irrational number on a flat surface…space time is not flat, even near Earth.

[SuperStingray]

I love the deep dive into how FTL communication with tachyons could work. Math might not always describe reality, but it's always great for the imagination!

[Salmach]

props for that Voyager comment .... was a good episode regardless.

[EinsteinsHair]

I wish you would do a video on why we cannot use entangled particles to send messages faster than light. In YouTube comments people often think we can. It would be great to be able to point them to your video. Now I have to explain to them that when we observe an entangled particle it takes on a random value, so we are just "sending" noise to the other particle. And even if we could send a signal, first you have to send many particles to a recipient at best at the speed of light.

A couple of times commenters have been confused about Hawking radiation and I've been able to simply tell them to watch Science Asylum's video on Hawking radiation.

[silverwind]

I have a big multilayer question for you. In your "what if you were made of light" video, you said that photons experience 0 time, as well as so much length contraction that the entire universe becomes completely flat. So, if, hypothetically speaking, you could instantaneously go at the speed of light and stop instantaneously, with no negative repercussions, as well as control where you end up once the universe expands, would you, in essence, have performed instantaneous teleportation to anywhere in the universe, or at least anywhere along a single direction, from your own point of view? If so, if you were to go FTL, would you experience yourself getting younger, since your personal time is going backwards? Also, would you be going through negative space or inverted space, and if so, what would either of those things be like and/or look like?

[TheAlchaemist]

I haven't seen other YT science channels tackle this specific subject despite tachyons being mentioned often. THANKS!

[numbersix]

I was able to follow this to the end, but not to my satisfaction as my math brain is too limited. But this is the first time I've heard this subject covered comprehensively. It's a great service you're providing.
Please keep doing the subjects YOU like!