Why do faster than light signals break spacetime?

Let's explore why faster than light signals reverse time and break causality. Why they can make effects occur before cause, causing time paradoxes.

This video is sponsored by Brilliant.

[AlekThunder]

"What will it be?" bartender asks. Tachyon walks into a bar.

[rajanvenkatesh]

Many videos ago, you said 'speed of light is actually speed of causality'.
With every fresh video, that is becoming clearer and clearer.
Thanks!

[abebuckingham]

If you don't understand the shirt in calculus if we consider x to be position and t to be time then the rate of change of the position over time is called dx/dt. The rate of change of velocity is acceleration and so it's d^2x/dt^2. The rate of change of acceleration is d^3x/dt^3 and the name for that is jerk. So the shirt says "Don't be a jerk".

[astrokevin]

Well done. I really liked the nested cause and effect circles. Great way of looking at this.

[YeOldeBelmont]

I love the energy you have while explaining things!

[dennisposadas]

Intuitively understood so easily by the end; marvelous, thank you!

[pujamathssolution]

Relativity is seriously a amazing topic to talk to the people's who likes it

[abdulqader]

I wish you SHOWED us at 22:14 how causality is broken when the fast observer send FTL message to stop the bomb. That was the most important part of the entire visualization of events

[vishnu_m]

Thank you! I've been waiting soo long to find video explaining this in simple way and since I found your channel I was hoping that one day you will touch this subject.
Big thanks!

[MarshallForLifeOfficial]

i love how you make everything so understandable keep doing what others don't i love it!!

[ImposterMalone]

First Video I see and I'm mainly disappointed because you're not just a floating head explaining physics.

[madlep]

The missile knows when it is in all reference frames. It knows this because it knows when it isn’t.

[sharmanraval]

i have to admit your are really smooth with the promos

[TheSmokingLizardSWE]

I don´t understand why it matters that causality is broken to observers as long as its not broken from the cause and effects "reality" as observed by them.

Even if something as in the example is launched 4xFTL in a 1LY distance, the message from an FTL observer to the effect would still reach the cause from the cause point of view after it has acted no matter how fast the message was transmitted.

[imagiro]

22:10 Intuitively I'd say, the problem is _transitioning_ a signal between slower-than-light and faster-than-light speeds. As long as the stl-"world" and ftl-world stay cleanly separated, causality doesn't break. Goes with what I heard, that the problem is _crossing_ the speed of light, not if you are below or above.
I have to think about that.
However: Reeeealy great video! Me like 😁

[jpe]

I have a suggestion for your next t-shirt: a graphic with three cartoon characters eating a puffed rice breakfast cereal, each character labeled d^4x/dt^4, d^5x/dt^5, and of course d^6x/dt^6

[nickwalden]

When we are in the original scenario, we looked at the length contraction from the missile POV. However, when looking at the FTL missile, you completely skip that step. I understand that the length contraction would make the distance imaginary, but it still seems like an important part of why things break at FTL.

[Life-mytl]

How is the causality broken in any of the cases discussed? As you said, what you see is not what is happening. So, even if the explosion is observed to happen before the missile is being launched. In reality, the effect is still following the cause. For example, we see lightning before the thunder. But anyhow the thunder occurred before the lightning. So, even if we are seeing the causality to break just because of seeing light signals in wrong order, that does not mean that the events have also occurred in wrong order. So the causality should not be broken even if the missile is travelling faster than light. Consequently, the argument that causality will break if an object travels faster than light should not stand. As an analogy, a supersonic aircraft travels faster than the speed of sound resulting in different effects without breaking the causality.

You explain well, in a very simple and entertaining way. Thank you, for sharing. Keep educating us.

[willmcgo]

Reminds me of videos where the distance is far enough, and a bullet is fired and travels faster than the speed of sound towards you, and you hear the bullet hit a target close by, then the sound of the gun firing is heard. Cody's Lab did a video on that.
Not sure how you could be traveling at the speed of sound past the target and still hear it get hit; that might be non-trivial.

[cslcchy]

22:21 But the problem is that this reverse phenomenon is only seen in the spaceship's perspective, no? Even if he sends a signal back, in the perspective of the shooter, the rocket has already launched. It is because of the limit of light's speed that the rocket is only seen after the boom occured.