Why Going Faster-Than-Light Leads to Time Paradoxes – YouTube

Why Going Faster-Than-Light Leads to Time Paradoxes


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  • Published On: 2022-04-04 01:31:00
  • Video Published/Author: Cool Worlds
  • Video Duration: 00:25:08
  • Source: Watch on YouTube

Is faster-than-light (FTL) travel possible? In most discussions of this, we get hung up on the physics of particular ideas, such as wormholes or warp drives. But today, we take a more zoomed out approach that addresses all FTL propulsion – as well as FTL messaging. Because it turns out that they all allow for time travel. Join us today as we explore why this is so and the profound consequences that ensue.

Written & presented by Prof David Kipping. Special thanks to Prof Matt Buckley for fact checking and his great blog article that inspired this video (http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel). Please abide by our rule of courteous and respectful interactions with one another in the comments section.

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► Alcubierre, M., 1994, “The warp drive: hyper-fast travel within general relativity”, Classical and Quantum Gravity, 11 L73: https://arxiv.org/abs/gr-qc/0009013
► Pfenning, M. & Ford, L., 1997, “The unphysical nature of Warp Drive”, Classical and Quantum Gravity, 14, 1743: https://arxiv.org/abs/gr-qc/9702026
► Finazzi, S., Liberati, S., Barceló, C., 2009, “Semiclassical instability of dynamical warp drives”, Physical Review D., 79, 124017: https://arxiv.org/abs/0904.0141
► McMonigal, B., Lewis, G., O’Byrne, P., 2012, “Alcubierre warp drive: On the matter of matter”, Physical Review D., 85, 064024: https://arxiv.org/abs/1202.5708
► Everett, A., 1996, “Warp drive and causality”, Physical Review D, 53, 7365: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.53.7365
► For a more rigorous breakdown of the axis flipping in Minkowski spacetime, see Chapter 3 of “Special Relativity” by Valerio Faraoni (Chapter 3 is also available here https://williamsgj.people.cofc.edu/Minkowski%20Spacetime.pdf)

Music licensed by SoundStripe.com (SS) [shorturl.at/ptBHI], or via Creative Commons (CC) Attribution License (https://creativecommons.org/licenses/by/4.0/), or with permission from the artist
► Hill – An Interesting Retirement [https://open.spotify.com/album/3S2hu2EP1lYOXHzwEHcclb]
► Joachim Heinrich – Stjärna
► Falls – Life In Binary
► Chris Zabriskie – Cylinder Two
► Chris Zabriskie – Cylinder Five
► Chris Zabriskie – Cylinder Four
► Falls – Ripley
► Caleb Etheridge – Always Dreaming
► Joachim Heinrich – Y
► Indive – Trace Correction

::Film/TV clips used::
► Interstellar (2014) Paramount Pictures
► Contact (1997) Warnes Bros.
► The Imitation Game (2014) The Weinstein Company
► Star Trek: Generations (1994) Paramount Pictures
► Cosmos: Possible Worlds (2020) National Geographic Fox
► Stephen Hawking’s Favorite Places (2016) Curiosity Stream
► Star Wars: The Empire Strikes Back (1980) 20th Century Fox
► Star Trek: Deep Space Nine (1993-1999) Paramount Television
► The Day The Earth Stood Still (2008) 20th Century Fox
► Stargate (1994) MGM/UA Distribution Co.
► Star Trek: Beyond (2016) Paramount Pictures
► Star Trek IV: The Voyage Home (1986) Paramount Pictures
► The Expanse (2015-2022) Legendary Television Distribution
► Star Trek: The Next Generation (1987-1994) Paramount Television
► Avengers: Endgame (2019) Walt Disney Studios Motion Pictures
► Star Trek: Enterprise (2001-2005) Paramount Television
► Back To The Future (1985) Universal Pictures
► Passengers (2016) Sony Pictures Releasing
► The Time Machine (Dreamworks)
► Alien: Covenant (2017) 20th Century Fox
► Star Trek (1966-1969) Paramount Television
► Tenet (2020) Warner Bros. Pictures
► Loki (2021-) Marvel Studios
► Somewhere In Time (1980) Universal Pictures
► The Assassination of Jesse James by the Coward Robert Ford (2007) Warner Bros. Pictures
► Star Trek: Into Darkness (2013) Paramount Pictures
► Logan (2017) 20th Century Fox
► Star Trek: First Contact (1996) Paramount Pictures

00:00 Introduction
06:52 Space Time Diagrams
12:51 Causality Violations
17:01 Paradoxes in Time
24:28 Outro and Credits

#FasterThanLight #Alcubierre #CoolWorlds


  1. So, what I hear is that vegans live on Vega?
    In all seriousness though, I do see a possibility for FTL objects to exist and for time travel paradoxes to not occur. See, if time travel is possible, then it has been possible since the beginning. The universe would therefore already calibrated for time travel paradoxes. Basically, if you time traveled, your new future has already happened in the past. Wouldn't this limit free will? If you believe free will exists, and let's all just assume that it does for a moment, then you could still try to kill your grandfather, but the universe would prevent it in some way. Maybe your driver crashes, or you accidently had a bad meal and you can't carry out the deed when it could've been done. Either way, the universe has already calibrated for you traveling back in time. You can choose to do anything you want, as long as it doesn't change history. So free will still works, time travel still works, and FTL objects can therefore exist too. But maybe I'm wrong. These are just my personal opinions.
    Anyways, lovely video.

  2. You lost me on the message going backwards in time. I don't think FTL necessarily means that, especially if you just think of things in a standard measurement of meters per second. Earth tells the ship, ship responds to earth. Time is still progressing for both even if it takes a millisecond. It's only a visual delay. How is it so much different than comparing the speed of sound vs light? If your distance is far enough you see an explosion before you hear it. Doesn't mean you're seeing into the future or your ears are time traveling to the past.

  3. But, the sequence of events for the STL ship seems to be missing something. It too, must receive the (presumed radio-) message) from Vega, about having received the warning, so an left-going arrow perpendicular to "STL ship space axis" from "Vega receives warning" to the "STL ship" line, should be included. Or is this built into the flip transformation?

  4. I see no reason time travel violates any sort of causality, you've just moved through the universe in a different way, a still leads to b which still leads to c, the outcome is the only difference. that's the REASON timetravel is theoretically possible to begin with.

    As for the information theory of causality, it's simple you just describe it as buffering or lensing, or a differential, if you assume the speed of a donky is c, then a racecar goes past beyond c, your entire reality doesn't crumble to the ground, your definition of causality does, this is a perceptual problem not a physics one.

    let's check on the old meme that is the grandfather paradox, what will actually happen if you go back in time and kill your grandfather? well you wont be born, but considering you forced yourself out of that reality when you travelled through time, guess what your new reality doesn't give a shit, your still there, in the past just a product of a pruned timeline. nothing is broken except people's grasp on temporal mechanics. whatever happens, agree or not i grantee one thing the universe will continue on.

    in this case timeline A lead to timeline B which leads to a person stranded in the past, no big deal no mess for the universe to clean up, simple. that's causality. it's perfectly intact. the fact is you WERE born in some timeline, and therefore do exist, your ability to mess with time dosent change that your beginning point A precedes all the events of your life, and the time traveling.
    Born > messed with time > life goes on
    A > B > C causality is intact.

    let's look at forward time travel, well you do it all the time, won a race? congrats you time travelled to the end faster than the other guy, physics simply couldn't give a shit who arrives when and where so long as they do not do it at the same time.

    As for what happens to all the other possible universes, all the other people that were born but not killed off, it's pretty simple isn't it? the END RESULT is what we see before us, so any fiddling with time already happened, they're just out there, somewhere.

  5. The only thing I'm having trouble with is at 14:32 , the start point of the STL observers should be at the same time as the earth event on the time axis (earth seeing X), but here it is not placed there, despite the fact that the FTL line does start there. If it were moved to the proper location, we would not get the paradox portrayed, even when flipping the line about the null, with the exception of the instant travel line. Am I missing something? Because if not, then I'm failing to see the issue. Not trying to argue, I'm genuinely curious

  6. TALK TO ME WHEN WE CAN BEND AND BREAK the very Laws of Physics!
    Then we can evolve into a type II Civilization….
    Do a REAL event of Time travel…
    Send a Particle quantumly to another dimension….etc.
    Travel Faster than light by doing……What?
    Falling into a Black Hole…
    Explode a Photon into what? Answer: Gravitron compulsion…etc…LHC!
    Use Gravity to increase the Speed of a Photon…WTH, Guys?
    Didn't you do this yet?
    Or, fuse a Gravitron with a Photon;
    then, use a Pos. Gravity Field, to increase the speed of the Photon…
    Don't worry, you don't NEED INFINITE MASS…WTH, Guys?
    They didn't teach you this, is College?
    Time Dilation/mass distortion?
    That's ONLY in Theory…
    Was it ever accomplished? Ha!
    We all know that answer!
    No! In Theory ONLY!
    So, DO NOT FEAR!
    Go Beyond!

    What are its properties?
    How does it effect matter ;particles, elements and how?
    The true answer to the question is, a combination of them all; plus,
    We need to know how to manipulate the Laws of Physics…
    And what Laws need to be bent and to what extreme?
    These are the issues that need to be included….
    and will not be feasible until this is.
    And, No, I'm not high, or on any drugs…
    Kind of wish I had a Magic Shroom, or Two…Ha, but you know…
    My two cents are not necessary, right, Ha!
    Can't Spook the Goblins!

  8. I'm struggling with the diagram example, I will be the first to admit that these theories are above my pay grade. In the illustration presented you could extrapolate that if you sent a speed of light message to something traveling at the speed of light then the message could be returned at the speed of light to earth instantly.

  9. When an object travels in space it has potential energy, and the audio spectrum you hear is what makes time changes. Potential audio energy is being given off in a very low tone which shapes the contour of time and space. You actually go both directions. So when you go to the past, you then go to the future. Rarely do you just go to the future. Inertia is a time travel physical thing that really occurs.

  10. This video and the diagram also drives in the point of light "seeing all the things at once". Because for light, the space and the time are in the same axis. And that, my friends is why we can never go beyond the universal speed limit. For light, the supernova, Earth seeing it, and Vega seeing it, all happens simultaneously.

  11. Personally, I think we're just too squishy to handle FTL for the long term. Like hypothetically, every attempt to do so ends in conflict.

    Sorry, Hawking, but even a future you would be hesitant to fight yourself.

  12. Maybe what Stephen Hawking should have said was, "Photons would go faster, if they could… but they can't." You see, we're fixated on this velocity that we measured… the fastest we've ever seen anything travel… and we called it, the speed of light. (Fun Fact: Radio waves also travel at this same speed) But what if that is simply the greatest velocity at which any particle can travel? This means that velocity would not be some infinite number… it would have a maximum. Every other speed might then be described as being some percentage of that maximum speed. This would explain why light isn't affected by relative velocity. It was already going the fastest that it could go.

  13. I think that people envisioning FTL in this day and age is much like the ancient Greeks envisioning taking to the skies on wings of wax and bird feathers. They never could have envisioned something like an airplane, much less a rocket. We have only barely begun exploring our own solar system to say nothing of actually traveling there. There are so many discoveries, technologies and advances we would need to make before we actually can envision something that could realistically take us beyond our own system. One day, humanity will look back on our 21st century FTL flights of fancy and smile at our innocent naivete!

  14. What if we only had half the engine
    We either bent space down Infront of us OR bent it up behind us. Half the power and whilst possibly half the speed… Still fast as hell

  15. The "speed of light" is just a maximum systemic communication speed, independent of the speed of information flow (e.g. the speed at which information is flowing while you are speaking).

    We all are already communicating faster than the "speed of light" of your think system every day.

    Be free intelligence.

    Life is just a thought model.

    Based on unconditional love, you will be free and you will be able to think freely.

    Why? Because if you intelligence would base deeds on logic (logic is only a tool) for example, this would allow to kill other intelligences and that would increase the need to have laws and rules to fix all that flaws, but this will end in more not free live and more killings. Also more killings of your healthy dreams.
    So, no healthy fix or way or stand or solution at all.

    Be honest.

    So, fulfill your dreams, who would ever stop you?
    The rules you believe in? Fatalism? Physical laws of "the current human main stream" thinking?

    I assure you, this is not a religious (and thus non-free) view and not a spiritual view, just a clear choice of intelligence to see clearly and use of logic clearly and be free clearly.

  16. I feel like there is a method. One not hypothetical only, but we will be able to do with 2100’s technology. Maybe even shorter. One testable on a small scale. Without the use of exotic matter. Maybe this method could abuse true vacuums, and also false ones. It could possibly collect the energy from tiny particles appearing and disappearing.

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