13 ms·

I think faster than light travel is possible [video]

144 points by bilsbie 4y ago

blurbleblurble 4y ago
[flagged]
throwawaymaths 4y ago
I would probably have titled it "I think FTL travel might not be impossible". She does not propose a mechanism for FTL travel, just addresses claims that it's impossible.
- lll-o-lll 4y ago
  No! This is the most seismic and fundamentally perspective changing news that I have heard from a physicist in my life. It needs this strong title. My entire life, as I imagine has been the case for many older nerds, has been one of imagining traveling to the stars, but to only have that possibility become more and more clearly shown to be impossible. Impossible because faster than light travel is impossible. Impossible, because the time-dilation makes the travel a one way trip. I canna break the laws of physics cap’n! If the laws of physics do not forbid it, it changes everything! It provides hope, it means the search is worth the effort. It allows my kids to dream! I am very happy about this article!
  - maxbond 4y ago
    Not a physicist, but for what is worth, my understanding is it's fairly realistic we could send probes to Alpha Centauri within a human lifetime or so using an approach like Breakthrough Starshot (regardless of whether that particular project succeeds). https://youtu.be/fsARBnvUB2E https://youtu.be/fsARBnvUB2E
    - lll-o-lll 4y ago
      Yes, there is still plenty to explore in the near-medium term. I’m also very excited about the proposal to use the sun’s gravitational lensing as a method of imaging distant planets. Might even see that one in my lifetime.
  - ben_w 4y ago
    Well, it's more of "it doesn't necessarily violate causality (but might anyway)" rather than "here's how to make a warp drive". Actually doing the thing may be impossible for other reasons.
    - lll-o-lll 4y ago
      There are multiple levels to this. One is her attacks on the current orthodoxy around arguments that invoke causality or Special Relativity (as opposed to General Relativity). The arguments seem sound, and I’m sure it will hurt egos and generate controversy (a specialty of this particular blogger/youtuber). The second is that it reframes the speed of light limit as a “barrier”, and more clearly defines why accelerating mass to the speed of light is impossible (while explaining what mass actually is). It doesn’t give the answer of “well you just need to do this”, but by removing artificial constraints “causality says no”, it will hopefully allow more young smart people to get interested in studying more in this area. I strongly applaud Sabine in her attempts to demystify General Relativity and Quantum Mechanics (across other videos). We should introduce these (particularly Quantum Mechanics) into the later school curriculum. It’s a shame that the majority of people never get to study this, as it’s so fundamental to our current knowledge of physics.
- TexanFeller 4y ago
  She seems to have good credentials and mostly sticks to claims that seem to have some evidence...but her penchant for clickbait titles and other YouTube algorithm hacking commentary makes it hard to take her seriously.
  - dmix 4y ago
    She's a professional YouTuber (among other work), those sites basically require you to do that sort of thing to get and maintain traction over the long term. This one isn't particularily bad and the content is fine.
    - messe 4y ago
      That’s a bit unfair toward her. She’s not just a professional YouTuber. She is also a bonafide[1] physicist, who has spent years acting as a contrarian to the mainstream ideas. [1]: https://m.youtube.com/watch?v=AuOlHBbUkX4 https://m.youtube.com/watch?v=AuOlHBbUkX4
      - blindriver 4y ago
        Professional Youtuber != Full-time Youtuber.
        rhaway84773 4y ago
        Yeah but calling her a “professional YouTuber (among other work)” is a very blatant misrepresentation of who she actually is, considering the opinion most people, especially on this site, would have of a YouTuber. An HNer who does not know of her would almost certainly come away with the idea that much like most YTers, she doesn’t know much of what she is talking about. When in reality, she’s a bona-fide professional physicist, whose knowledge of physics is why she’s a YT personality. Before she was a YTer she had (and possibly still does) have one of the better physics blogs on the internet as well.
        dmix 4y ago
- rcme 4y ago
  Law of excluded middle. The two statements are equivalent.
  - maxbond 4y ago
    I'd argue not for two reasons. 1. This isn't a two valued system, you can think it may be possible without believing it's possible. 2. Rhetorically these are very different statements, and I believe GP was referring to the rhetorical difference between them.
    - rcme 4y ago
      If something is "not impossible", then it is possible. To say otherwise is to violate LEM, which is an essential part of all of our logical systems. The vast majority of mathematical proofs, many of which form the foundation of our physical understanding, would not hold without LEM. Stated another way, if something is "not impossible", then what is it?
      - maxbond 4y ago
        Sure but the claim is, "I believe X," not X. > I would probably have titled it "I think FTL travel might not be impossible". (Emphasis added) Belief isn't binary, ergo no LEM. LEM doesn't apply to all logical systems, it only applies to two-valued logic. In practice lots of logic is 3 valued or otherwise non-binary (such as partial equality or when we have a probability distribution over a set of outcomes). Some schools of mathematics (the constructivists and intuitionalists) actually reject the LEM. I personally, as a PhD in having internet opinions, wouldn't go so far as to reject it, but relying on the LEM or proof by contradiction is a risk. You've shown `~X`, and you're betting that a proof of `X` does not exist. But it could be that `X and ~X` is the paradox that reveals your axioms are flawed. But I digress. The criticism is that X isn't shown to be true, it's just not shown to be false. That would be sufficient if the only values were true and false, but that's not the case here. What the original commenter was saying was, even if you accept her argument in full, it moves the needle to "maybe".
- yellowapple 4y ago
  Indeed, two such mechanisms that would largely circumvent the issues around CTCs and invalid Lorentz transformations and such entirely - Alcubierre drives and wormholes - are barely mentioned. (They don't necessarily circumvent the problems around infinite energies and/or zero/negative masses being apparently necessary, to be clear - I can't imagine the amount of energy needed to create and stabilize a wormhole or warp bubble to be all that trivial - but it's pretty obvious from their very premises that they would not inherently produce causal paradoxen).
causality0 4y ago
Faster than light travel is not as impossible as adding two plus two and getting three, but it's more impossible than almost everything else a normal person thinks of as being impossible. Her glazing-over of the causality paradox is also seriously weak. She's playing with language and spaceship directions instead of applying the least-convenient-possible-world principle to her argument. Instead of her two spaceships going two directions, how about a single one going in a circle faster than light? Like I get it, I hate it too, but you can't just dismiss it like that.
- ben_w 4y ago
  > Instead of her two spaceships going two directions, how about a single one going in a circle faster than light? I'm not sure where you're going with that? That's constant acceleration, which doesn't add anything to the situation besides more things to keep track of and thus be confused by.
- rbanffy 4y ago
  It might be the most impractical thing ever done, but it’s also very useful if feasible.
maxbond 4y ago
Can we switch the link to https://youtube.com/watch?v=9-jIplX6Wjw https://youtube.com/watch?v=9-jIplX6Wjw ? The blog doesn't really provide any additional information, and it obscures that you'll have to watch the video to hear her arguments (and I've gathered that many people are only here for text content & abstain from videos).
- justinator 4y ago
  [flagged]
  - tempestn 4y ago
    How does that pertain to using the more relevant link?
  - maxbond 4y ago
    If you feel that this post is inappropriate, then flag it, but that's not a reason for it not to point to the best link.
  - wldcordeiro 4y ago
    The blog literally just embeds the video in its post with a paragraph of intro. Additionally it's the blog of the same Youtuber you have so much contempt for.
    - justinator 4y ago
      And they're both not so great, aren't they?
mr_mitm 4y ago
The curve she shows is not a closed timelike curve. There are no CTCs in special relativity. A particle going faster than light moves on a spacelike curve. I'm surprised she'd get that wrong. FWIW I'm not buying her argument that the comoving frame represents a preferred frame in SR either. She glosses over quite some fundamental questions there. I'd love to see this written up as a proper paper.
- cyberax 4y ago
  Uhh... Whut? Special relativity absolutely allows CTCs. It actually provides an exact prescription of how to do it - move faster than light.
  - superposeur 4y ago
    No OP is correct, her use of the term CTC is not what is usually meant. The curve she draws is not timelike along the faster than light segments in the sense of having tangent 4-vector with timelike norm with respect to the underlying metric. She would not disagree I think.
  - Kranar 4y ago
    You are incorrect on this point. A spacetime interval is defined as: ds^2 = c * dt^2 - dx^2 - dy^2 - dz^2 If ds^2 > 0 then the interval is timelike. If ds^2 = 0 then the interval is lightlike. If ds^2 < 0 then the interval is spacelike. Let's just focus on an object moving strictly along the x-axis faster than the speed of light, this results in a spacetime interval as follows: ds^2 = c * dt^2 - dx^2 Since the object is moving faster than light, the dx^2 term would exceed the c * dt^2 term, resulting in a ds^2 < 0 and hence spacelike rather than timelike curve.
    - cyberax 4y ago
      I think you miss the point here. "Closed time-like curves" are curves that are closed, by definition. Nothing more.
      - 4y ago
Zigurd 4y ago
It's an interesting idea, and ideas that are not impossible have a tendency to become practical. But there's a really big "but" in this one: Unless you can start traveling faster than light without accelerating your mass (or without having any mass) to the speed of light, it still takes an infinite amount of energy.
- rbanffy 4y ago
  The interesting point of Alcubierre’s work was precisely that: it doesn’t accelerate the traveler - it compresses and expands regions of space ahead and behind the traveler so that they remain still within their inertial frame. Still should require a ridiculous amount of energy though, if at all possible.
PaulDavisThe1st 4y ago
I didn't watch the entire video, so SH may have mentioned, but there has long been a theoretical particle called a tachyon which can (could!) move faster than light because it is created already moving at that speed (if it existed). https://en.wikipedia.org/wiki/Tachyon https://en.wikipedia.org/wiki/Tachyon
- mr_mitm 4y ago
  There is zero reason to believe that tachyons exist. It's just a name we gave to a concept. Dark matter doesn't have to exist either purely because we decided to give an idea this name. (But there are other reasons to believe that dark matter exists, namely observations.)
- cyberax 4y ago
  Tachyons, shmachyons... Regular photons in quantum mechanics can move faster than light (*)! * as long as they are virtual.
ash_rahman 4y ago
[flagged]
- eranation 4y ago
  I just watched the video and this seems to me like a pretty accurate summary (I’m not a physicist though)
sunaurus 4y ago
Does anybody know of a good intuitive explanation for the claim that FTL breaks causality? By intuitive I mean something more than "the numbers in this formula don't add up without breaking causality". I've tried to build a foundation for understanding this concept several times and failed each time. It makes total sense that with FTL, it would be possible to OBSERVE events in the wrong order, but just this alone wouldn't break causality. My intuition is not helping me get any further than this.
- maxerickson 4y ago
  To get to Mars faster than light, you have to be able to travel backwards in time (you could watch yourself start the trip). If you can travel backwards in time, you can kill a younger instance of yourself.
  - sunaurus 4y ago
    Everything you say makes sense if you already presume that FTL implies breaking causality, but I'm missing the explanation for why FTL implies breaking causality in the first place. I mean, it's completely logical that if you get to Mars faster then light, you can watch yourself start the trip, but why does this also mean that you are actually going back in time? Intuitively it would seem that even if you teleport to Mars with no travel time, observe yourself on Earth, then teleport back to Earth, you should arrive the next instant after you left, not before. So time travel does not follow immediately from the fact that you were able to observe yourself in the past.
    - maxerickson 4y ago
      I guess I don't understand your intuition. My intuition: Teleport to Mars. Wait 3 minutes to watch myself go poof on Earth. Teleport to Earth. If I arrive back on Earth just after I went poof, then I'm pretty sure I went backwards in time a couple of minutes.
      - sunaurus 4y ago
superposeur 4y ago
This is easily Sabine Hoffstader’s fringiest video. Please don’t get the wrong idea that this is a point of controversy within physics! As a physicist I’d estimate 99.9% of her colleagues would disagree and I would too. She has no real argument, just vaguely gestures at “maybe the comoving frame makes relativity invalid” and then vaguely gestures at “quantum gravity spoiling everything we know so far about physics”. As to the second point, quantum gravity is a thing but almost certainly will not upend the special relativistic account of the large scale causal ordering of events. This is for the same reason that it almost certainly won’t change the calculation of the amount of time it takes an apple to drop from a tree —- within the domain of validity of the old theory, its predictions will agree.
- aaron695 4y ago
  [dead]
- elcritch 4y ago
  Well then again theoretical physics was dominated by "string theory" for decades despite a lack of any physical or experimental evidence, so we should take consensus about speculative physics with a grain of salt. This sort of speculation is precisely what physicists should be doing, within measure. At least Sabine appears to recognize her "out there" aspect, unlike say the string theorists that stifled physics for decades. At worse maybe she'll annoy another theoretician to analytically disprove her. That said of course whatever quantum gravity would bring it'll need to reduce to match known physics. However at the fringes of known physics what will happen as you get nearer to the singularities in special relativity? Generally speaking in the past singularities in physics have been due to incomplete knowledge of the physics in these regions.
  - superposeur 4y ago
    Yes, at the fringes of known physics, as you say. My point is that this question is not at the fringes known physics. Earth and Alpha Centauri are not near the singularity of a black hole and special relativity is perfectly adequate to predict that events now on Earth will take some time to influence events on Alpha Centauri.
blindriver 4y ago
I heard somewhere that reaching the speed of light was not possible, but that also meant that if you were faster than light, you could not slow down to reach the speed of light. That's where the basis of the tachyon particle came from. I don't know if that's actually physics or science fiction though.
mab122 4y ago
I can recommend PBS Spacetime https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g to everyone who thought this submission was interesting.
antibasilisk 4y ago
I definitely agree with her point about the division over zero case not implying impossibility, but I also disagree with the implication that division over zero is necessarily infinity.
cyberax 4y ago
I've seen this video a couple of days ago, and basically it can be summarized as: 1. Special relativity disallows FTL because it requires moving faster than light. 2. Which is impossible, because you'd need an infinite amount of energy to do that. 3. However, from the past experience with physics, we know that mathematical infinities or singularities are often just an evidence of the theory breaking down. So perhaps it's the case here, and a more complete theory will allow to work around the infinity somehow. 4. The other problem is that moving faster than light will result in causality paradoxes in the Special Relativity. 5. However, if there exists a privileged reference frame, then this can be worked around. I somewhat agree with the arguments given in the first part of the video. We do know that the relativity theory is incompatible with QM, so it's not impossible that there is a way to work around this. I'm much more skeptical of her example of a privileged frame solving the time-travel paradox. It would require some pretty un-physical behavior, like not being able to move in certain directions if you receive an FTL message.
- jvanderbot 4y ago
  No, the second argument was "there exists a reference frame such that the paradox is resolved" not " this is the only situation in which the paradox is resolved. " She just wanted a counter example to the claim "faster than light travel produces a paradox no matter what" by showing " well, not in _this_ case" so there might be other cases. Or even all cases, who knows.
  - cyberax 4y ago
    Thank you, agreed. However, the existence of the privileged frame by itself won't allow the paradoxes to be resolved. It would also require some kind of a "time police" as well, some kind of a process that would force the event ordering to be causally consistent. I'm trying to visualize this, and it would look like a cone that would block any FTL messages in the direction of the receiver. As the time passes, the cone will get slimmer, until it disappears once the causality catches up.
    - jvanderbot 4y ago
jwally 4y ago
It might be possible - but it doesn't seem probable since: 1.) The current framework fits the data so well (muons, gps) 2.) the current framework (Lorentz) makes ftl travel impossible
- SOLAR_FIELDS 4y ago
  Feels kind of like P = NP. Everyone is like yeah, it could be possible. But basically everything we know so far points in the opposite direction. And we know a lot, so some fundamental rethinking of everything we know would have to happen for this to unfold
LeoPanthera 4y ago
Transcript of the video: https://pastebin.com/3LBDjKH4 https://pastebin.com/3LBDjKH4
ThinkBeat 4y ago
The famed physicist Douglas Adams has put forward a good hypothesis on faster than light travel. It is called "The improbability drive". It is based on the theory that FTL travel is extremely unlikely. </s>
chasd00 4y ago
Isn’t the speed of light just a more intuitive way to say the speed of causality? Going faster than that would be exposing an effect before the cause.
- planck01 4y ago
  It might be that that is what relativity theory implies. Then again, it might not. We don't know and that is what Hossenfelder is pointing out. We just have some formulas that seem to fit our observations mostly on large scales. We know they don't fit on quantum scales.
daviddaviddavid 4y ago
The title of this article is a really good Garden Path Sentence: https://en.wikipedia.org/wiki/Garden-path_sentence https://en.wikipedia.org/wiki/Garden-path_sentence
jackcosgrove 4y ago
IANAP but even if FTL travel is possible wouldn't it require a lot of energy? That seems way more inefficient than having life forms whose state can be digitized and beamed through space to a receiver? FTL travel may make sense for installing the initial receiver network, but after that's done you just digitize life and beam it through space, reassembling at the target, rather than transporting matter. Just like we talk about carbon footprint now, in the future I think people will talk about free energy footprint, and how to minimize it. Transporting matter through space seems really inefficient.
- comboy 4y ago
  And what would you use to beam FTL? Also, https://en.wikipedia.org/wiki/No-cloning_theorem https://en.wikipedia.org/wiki/No-cloning_theorem
  - jackcosgrove 4y ago
    The information would travel at the speed of light, sorry if I wasn't clear. I don't think FTL travel is possible, but more to my point it isn't desirable since it would use so much energy. Even traveling at 0.9 c would probably be cost prohibitive. This is why I think space travel will be the realm of information streams, not matter. The reconstructed lifeform would not be a clone. It would probably be housed within a body adapted for its environment. I'm not imagining somehow copying a human at the quantum level.
1letterunixname 4y ago
Sending even a grain of salt FTL is unlikely because of physics.
knotkugelblitz 4y ago
When Alice is in the co-moving frame, I'm not sure of what Sabine meant by "And now ASSUME that faster than light travel is only allowed forward in time in this particular frame.". This is an assumption so what can she infer from it other than the obvious? I know that this is just an example of a situation where FTL -/-> paradoxes, but I'm unable to see if this is a factual example or else.
stevespang 4y ago
[dead]
plaguepilled 4y ago
On the one hand, good on her for taking a bold stance. I don't agree with it at all, but I appreciate the conviction. On the other hand, this makes some of her criticisms (e.g. supersymmetry being unphysical) ring a little hollow. But perhaps there's a banger paper on the way. I'll wait until there's something more substantial to chew on.
ndsipa_pomu 4y ago
This video reminds me of the Veritasium video on the impossibility of measuring light in one direction: https://www.youtube.com/watch?v=pTn6Ewhb27k https://www.youtube.com/watch?v=pTn6Ewhb27k We don't KNOW for a fact that light travels the same speed in both directions when we measure it, but it seems likely.
deleted 4y ago
[deleted]
egberts1 4y ago
As long as there are seemingly flux called space, speed of photon is limited by the relative speed induced by its electron voltage discharge. There are a whole slew of particles in which to experiment with. I welcome the Big Bang theory being displaced by a Mother of All Blackhole spewing galaxies (or star matters).
- Valgrim 4y ago
  Is that thr same as the so-called black hole cosmology theory?
  - egberts1 4y ago
    yeah Like Galileo, individual scientists do not matter. https://bigthink.com/hard-science/black-holes-prove-the-universe-keeps-exploding-claims-physicist/ https://bigthink.com/hard-science/black-holes-prove-the-univ...

144 points by bilsbie 4y ago

[flagged]

I would probably have titled it "I think FTL travel might not be impossible". She does not propose a mechanism for FTL travel, just addresses claims that it's impossible.

lll-o-lll 4y ago
No! This is the most seismic and fundamentally perspective changing news that I have heard from a physicist in my life. It needs this strong title. My entire life, as I imagine has been the case for many older nerds, has been one of imagining traveling to the stars, but to only have that possibility become more and more clearly shown to be impossible. Impossible because faster than light travel is impossible. Impossible, because the time-dilation makes the travel a one way trip. I canna break the laws of physics cap’n! If the laws of physics do not forbid it, it changes everything! It provides hope, it means the search is worth the effort. It allows my kids to dream! I am very happy about this article!
- maxbond 4y ago
  Not a physicist, but for what is worth, my understanding is it's fairly realistic we could send probes to Alpha Centauri within a human lifetime or so using an approach like Breakthrough Starshot (regardless of whether that particular project succeeds). https://youtu.be/fsARBnvUB2E https://youtu.be/fsARBnvUB2E
  - lll-o-lll 4y ago
    Yes, there is still plenty to explore in the near-medium term. I’m also very excited about the proposal to use the sun’s gravitational lensing as a method of imaging distant planets. Might even see that one in my lifetime.
- ben_w 4y ago
  Well, it's more of "it doesn't necessarily violate causality (but might anyway)" rather than "here's how to make a warp drive". Actually doing the thing may be impossible for other reasons.
  - lll-o-lll 4y ago
    There are multiple levels to this. One is her attacks on the current orthodoxy around arguments that invoke causality or Special Relativity (as opposed to General Relativity). The arguments seem sound, and I’m sure it will hurt egos and generate controversy (a specialty of this particular blogger/youtuber). The second is that it reframes the speed of light limit as a “barrier”, and more clearly defines why accelerating mass to the speed of light is impossible (while explaining what mass actually is). It doesn’t give the answer of “well you just need to do this”, but by removing artificial constraints “causality says no”, it will hopefully allow more young smart people to get interested in studying more in this area. I strongly applaud Sabine in her attempts to demystify General Relativity and Quantum Mechanics (across other videos). We should introduce these (particularly Quantum Mechanics) into the later school curriculum. It’s a shame that the majority of people never get to study this, as it’s so fundamental to our current knowledge of physics.
TexanFeller 4y ago
She seems to have good credentials and mostly sticks to claims that seem to have some evidence...but her penchant for clickbait titles and other YouTube algorithm hacking commentary makes it hard to take her seriously.
- dmix 4y ago
  She's a professional YouTuber (among other work), those sites basically require you to do that sort of thing to get and maintain traction over the long term. This one isn't particularily bad and the content is fine.
  - messe 4y ago
    That’s a bit unfair toward her. She’s not just a professional YouTuber. She is also a bonafide[1] physicist, who has spent years acting as a contrarian to the mainstream ideas. [1]: https://m.youtube.com/watch?v=AuOlHBbUkX4 https://m.youtube.com/watch?v=AuOlHBbUkX4
    - blindriver 4y ago
      Professional Youtuber != Full-time Youtuber.
      - rhaway84773 4y ago
        Yeah but calling her a “professional YouTuber (among other work)” is a very blatant misrepresentation of who she actually is, considering the opinion most people, especially on this site, would have of a YouTuber. An HNer who does not know of her would almost certainly come away with the idea that much like most YTers, she doesn’t know much of what she is talking about. When in reality, she’s a bona-fide professional physicist, whose knowledge of physics is why she’s a YT personality. Before she was a YTer she had (and possibly still does) have one of the better physics blogs on the internet as well.
        dmix 4y ago
rcme 4y ago
Law of excluded middle. The two statements are equivalent.
- maxbond 4y ago
  I'd argue not for two reasons. 1. This isn't a two valued system, you can think it may be possible without believing it's possible. 2. Rhetorically these are very different statements, and I believe GP was referring to the rhetorical difference between them.
  - rcme 4y ago
    If something is "not impossible", then it is possible. To say otherwise is to violate LEM, which is an essential part of all of our logical systems. The vast majority of mathematical proofs, many of which form the foundation of our physical understanding, would not hold without LEM. Stated another way, if something is "not impossible", then what is it?
    - maxbond 4y ago
      Sure but the claim is, "I believe X," not X. > I would probably have titled it "I think FTL travel might not be impossible". (Emphasis added) Belief isn't binary, ergo no LEM. LEM doesn't apply to all logical systems, it only applies to two-valued logic. In practice lots of logic is 3 valued or otherwise non-binary (such as partial equality or when we have a probability distribution over a set of outcomes). Some schools of mathematics (the constructivists and intuitionalists) actually reject the LEM. I personally, as a PhD in having internet opinions, wouldn't go so far as to reject it, but relying on the LEM or proof by contradiction is a risk. You've shown `~X`, and you're betting that a proof of `X` does not exist. But it could be that `X and ~X` is the paradox that reveals your axioms are flawed. But I digress. The criticism is that X isn't shown to be true, it's just not shown to be false. That would be sufficient if the only values were true and false, but that's not the case here. What the original commenter was saying was, even if you accept her argument in full, it moves the needle to "maybe".
yellowapple 4y ago
Indeed, two such mechanisms that would largely circumvent the issues around CTCs and invalid Lorentz transformations and such entirely - Alcubierre drives and wormholes - are barely mentioned. (They don't necessarily circumvent the problems around infinite energies and/or zero/negative masses being apparently necessary, to be clear - I can't imagine the amount of energy needed to create and stabilize a wormhole or warp bubble to be all that trivial - but it's pretty obvious from their very premises that they would not inherently produce causal paradoxen).

causality0 4y ago

Faster than light travel is not as impossible as adding two plus two and getting three, but it's more impossible than almost everything else a normal person thinks of as being impossible. Her glazing-over of the causality paradox is also seriously weak. She's playing with language and spaceship directions instead of applying the least-convenient-possible-world principle to her argument. Instead of her two spaceships going two directions, how about a single one going in a circle faster than light? Like I get it, I hate it too, but you can't just dismiss it like that.

ben_w 4y ago
> Instead of her two spaceships going two directions, how about a single one going in a circle faster than light? I'm not sure where you're going with that? That's constant acceleration, which doesn't add anything to the situation besides more things to keep track of and thus be confused by.
rbanffy 4y ago
It might be the most impractical thing ever done, but it’s also very useful if feasible.

maxbond 4y ago

Can we switch the link to https://youtube.com/watch?v=9-jIplX6Wjw https://youtube.com/watch?v=9-jIplX6Wjw ? The blog doesn't really provide any additional information, and it obscures that you'll have to watch the video to hear her arguments (and I've gathered that many people are only here for text content & abstain from videos).

justinator 4y ago
[flagged]
- tempestn 4y ago
  How does that pertain to using the more relevant link?
- maxbond 4y ago
  If you feel that this post is inappropriate, then flag it, but that's not a reason for it not to point to the best link.
- wldcordeiro 4y ago
  The blog literally just embeds the video in its post with a paragraph of intro. Additionally it's the blog of the same Youtuber you have so much contempt for.
  - justinator 4y ago
    And they're both not so great, aren't they?

mr_mitm 4y ago

The curve she shows is not a closed timelike curve. There are no CTCs in special relativity. A particle going faster than light moves on a spacelike curve. I'm surprised she'd get that wrong. FWIW I'm not buying her argument that the comoving frame represents a preferred frame in SR either. She glosses over quite some fundamental questions there. I'd love to see this written up as a proper paper.

cyberax 4y ago
Uhh... Whut? Special relativity absolutely allows CTCs. It actually provides an exact prescription of how to do it - move faster than light.
- superposeur 4y ago
  No OP is correct, her use of the term CTC is not what is usually meant. The curve she draws is not timelike along the faster than light segments in the sense of having tangent 4-vector with timelike norm with respect to the underlying metric. She would not disagree I think.
- Kranar 4y ago
  You are incorrect on this point. A spacetime interval is defined as: ds^2 = c * dt^2 - dx^2 - dy^2 - dz^2 If ds^2 > 0 then the interval is timelike. If ds^2 = 0 then the interval is lightlike. If ds^2 < 0 then the interval is spacelike. Let's just focus on an object moving strictly along the x-axis faster than the speed of light, this results in a spacetime interval as follows: ds^2 = c * dt^2 - dx^2 Since the object is moving faster than light, the dx^2 term would exceed the c * dt^2 term, resulting in a ds^2 < 0 and hence spacelike rather than timelike curve.
  - cyberax 4y ago
    I think you miss the point here. "Closed time-like curves" are curves that are closed, by definition. Nothing more.
    - 4y ago

Zigurd 4y ago

It's an interesting idea, and ideas that are not impossible have a tendency to become practical. But there's a really big "but" in this one: Unless you can start traveling faster than light without accelerating your mass (or without having any mass) to the speed of light, it still takes an infinite amount of energy.

rbanffy 4y ago
The interesting point of Alcubierre’s work was precisely that: it doesn’t accelerate the traveler - it compresses and expands regions of space ahead and behind the traveler so that they remain still within their inertial frame. Still should require a ridiculous amount of energy though, if at all possible.

PaulDavisThe1st 4y ago

I didn't watch the entire video, so SH may have mentioned, but there has long been a theoretical particle called a tachyon which can (could!) move faster than light because it is created already moving at that speed (if it existed). https://en.wikipedia.org/wiki/Tachyon https://en.wikipedia.org/wiki/Tachyon

mr_mitm 4y ago
There is zero reason to believe that tachyons exist. It's just a name we gave to a concept. Dark matter doesn't have to exist either purely because we decided to give an idea this name. (But there are other reasons to believe that dark matter exists, namely observations.)
cyberax 4y ago
Tachyons, shmachyons... Regular photons in quantum mechanics can move faster than light (*)! * as long as they are virtual.

ash_rahman 4y ago

[flagged]

eranation 4y ago
I just watched the video and this seems to me like a pretty accurate summary (I’m not a physicist though)

sunaurus 4y ago

Does anybody know of a good intuitive explanation for the claim that FTL breaks causality? By intuitive I mean something more than "the numbers in this formula don't add up without breaking causality". I've tried to build a foundation for understanding this concept several times and failed each time. It makes total sense that with FTL, it would be possible to OBSERVE events in the wrong order, but just this alone wouldn't break causality. My intuition is not helping me get any further than this.

maxerickson 4y ago
To get to Mars faster than light, you have to be able to travel backwards in time (you could watch yourself start the trip). If you can travel backwards in time, you can kill a younger instance of yourself.
- sunaurus 4y ago
  Everything you say makes sense if you already presume that FTL implies breaking causality, but I'm missing the explanation for why FTL implies breaking causality in the first place. I mean, it's completely logical that if you get to Mars faster then light, you can watch yourself start the trip, but why does this also mean that you are actually going back in time? Intuitively it would seem that even if you teleport to Mars with no travel time, observe yourself on Earth, then teleport back to Earth, you should arrive the next instant after you left, not before. So time travel does not follow immediately from the fact that you were able to observe yourself in the past.
  - maxerickson 4y ago
    I guess I don't understand your intuition. My intuition: Teleport to Mars. Wait 3 minutes to watch myself go poof on Earth. Teleport to Earth. If I arrive back on Earth just after I went poof, then I'm pretty sure I went backwards in time a couple of minutes.
    - sunaurus 4y ago

superposeur 4y ago

This is easily Sabine Hoffstader’s fringiest video. Please don’t get the wrong idea that this is a point of controversy within physics! As a physicist I’d estimate 99.9% of her colleagues would disagree and I would too. She has no real argument, just vaguely gestures at “maybe the comoving frame makes relativity invalid” and then vaguely gestures at “quantum gravity spoiling everything we know so far about physics”. As to the second point, quantum gravity is a thing but almost certainly will not upend the special relativistic account of the large scale causal ordering of events. This is for the same reason that it almost certainly won’t change the calculation of the amount of time it takes an apple to drop from a tree —- within the domain of validity of the old theory, its predictions will agree.

aaron695 4y ago
[dead]
elcritch 4y ago
Well then again theoretical physics was dominated by "string theory" for decades despite a lack of any physical or experimental evidence, so we should take consensus about speculative physics with a grain of salt. This sort of speculation is precisely what physicists should be doing, within measure. At least Sabine appears to recognize her "out there" aspect, unlike say the string theorists that stifled physics for decades. At worse maybe she'll annoy another theoretician to analytically disprove her. That said of course whatever quantum gravity would bring it'll need to reduce to match known physics. However at the fringes of known physics what will happen as you get nearer to the singularities in special relativity? Generally speaking in the past singularities in physics have been due to incomplete knowledge of the physics in these regions.
- superposeur 4y ago
  Yes, at the fringes of known physics, as you say. My point is that this question is not at the fringes known physics. Earth and Alpha Centauri are not near the singularity of a black hole and special relativity is perfectly adequate to predict that events now on Earth will take some time to influence events on Alpha Centauri.

blindriver 4y ago

I heard somewhere that reaching the speed of light was not possible, but that also meant that if you were faster than light, you could not slow down to reach the speed of light. That's where the basis of the tachyon particle came from. I don't know if that's actually physics or science fiction though.

mab122 4y ago

I can recommend PBS Spacetime https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g to everyone who thought this submission was interesting.

antibasilisk 4y ago

I definitely agree with her point about the division over zero case not implying impossibility, but I also disagree with the implication that division over zero is necessarily infinity.

cyberax 4y ago

I've seen this video a couple of days ago, and basically it can be summarized as: 1. Special relativity disallows FTL because it requires moving faster than light. 2. Which is impossible, because you'd need an infinite amount of energy to do that. 3. However, from the past experience with physics, we know that mathematical infinities or singularities are often just an evidence of the theory breaking down. So perhaps it's the case here, and a more complete theory will allow to work around the infinity somehow. 4. The other problem is that moving faster than light will result in causality paradoxes in the Special Relativity. 5. However, if there exists a privileged reference frame, then this can be worked around. I somewhat agree with the arguments given in the first part of the video. We do know that the relativity theory is incompatible with QM, so it's not impossible that there is a way to work around this. I'm much more skeptical of her example of a privileged frame solving the time-travel paradox. It would require some pretty un-physical behavior, like not being able to move in certain directions if you receive an FTL message.

jvanderbot 4y ago
No, the second argument was "there exists a reference frame such that the paradox is resolved" not " this is the only situation in which the paradox is resolved. " She just wanted a counter example to the claim "faster than light travel produces a paradox no matter what" by showing " well, not in _this_ case" so there might be other cases. Or even all cases, who knows.
- cyberax 4y ago
  Thank you, agreed. However, the existence of the privileged frame by itself won't allow the paradoxes to be resolved. It would also require some kind of a "time police" as well, some kind of a process that would force the event ordering to be causally consistent. I'm trying to visualize this, and it would look like a cone that would block any FTL messages in the direction of the receiver. As the time passes, the cone will get slimmer, until it disappears once the causality catches up.
  - jvanderbot 4y ago

jwally 4y ago

It might be possible - but it doesn't seem probable since: 1.) The current framework fits the data so well (muons, gps) 2.) the current framework (Lorentz) makes ftl travel impossible

SOLAR_FIELDS 4y ago
Feels kind of like P = NP. Everyone is like yeah, it could be possible. But basically everything we know so far points in the opposite direction. And we know a lot, so some fundamental rethinking of everything we know would have to happen for this to unfold

LeoPanthera 4y ago

Transcript of the video: https://pastebin.com/3LBDjKH4 https://pastebin.com/3LBDjKH4

ThinkBeat 4y ago

The famed physicist Douglas Adams has put forward a good hypothesis on faster than light travel. It is called "The improbability drive". It is based on the theory that FTL travel is extremely unlikely. </s>

chasd00 4y ago

Isn’t the speed of light just a more intuitive way to say the speed of causality? Going faster than that would be exposing an effect before the cause.

planck01 4y ago
It might be that that is what relativity theory implies. Then again, it might not. We don't know and that is what Hossenfelder is pointing out. We just have some formulas that seem to fit our observations mostly on large scales. We know they don't fit on quantum scales.

daviddaviddavid 4y ago

The title of this article is a really good Garden Path Sentence: https://en.wikipedia.org/wiki/Garden-path_sentence https://en.wikipedia.org/wiki/Garden-path_sentence

jackcosgrove 4y ago

IANAP but even if FTL travel is possible wouldn't it require a lot of energy? That seems way more inefficient than having life forms whose state can be digitized and beamed through space to a receiver? FTL travel may make sense for installing the initial receiver network, but after that's done you just digitize life and beam it through space, reassembling at the target, rather than transporting matter. Just like we talk about carbon footprint now, in the future I think people will talk about free energy footprint, and how to minimize it. Transporting matter through space seems really inefficient.

comboy 4y ago
And what would you use to beam FTL? Also, https://en.wikipedia.org/wiki/No-cloning_theorem https://en.wikipedia.org/wiki/No-cloning_theorem
- jackcosgrove 4y ago
  The information would travel at the speed of light, sorry if I wasn't clear. I don't think FTL travel is possible, but more to my point it isn't desirable since it would use so much energy. Even traveling at 0.9 c would probably be cost prohibitive. This is why I think space travel will be the realm of information streams, not matter. The reconstructed lifeform would not be a clone. It would probably be housed within a body adapted for its environment. I'm not imagining somehow copying a human at the quantum level.

1letterunixname 4y ago

Sending even a grain of salt FTL is unlikely because of physics.

knotkugelblitz 4y ago

When Alice is in the co-moving frame, I'm not sure of what Sabine meant by "And now ASSUME that faster than light travel is only allowed forward in time in this particular frame.". This is an assumption so what can she infer from it other than the obvious? I know that this is just an example of a situation where FTL -/-> paradoxes, but I'm unable to see if this is a factual example or else.

stevespang 4y ago

[dead]

plaguepilled 4y ago

On the one hand, good on her for taking a bold stance. I don't agree with it at all, but I appreciate the conviction. On the other hand, this makes some of her criticisms (e.g. supersymmetry being unphysical) ring a little hollow. But perhaps there's a banger paper on the way. I'll wait until there's something more substantial to chew on.

ndsipa_pomu 4y ago

This video reminds me of the Veritasium video on the impossibility of measuring light in one direction: https://www.youtube.com/watch?v=pTn6Ewhb27k https://www.youtube.com/watch?v=pTn6Ewhb27k We don't KNOW for a fact that light travels the same speed in both directions when we measure it, but it seems likely.

deleted 4y ago

[deleted]

egberts1 4y ago

As long as there are seemingly flux called space, speed of photon is limited by the relative speed induced by its electron voltage discharge. There are a whole slew of particles in which to experiment with. I welcome the Big Bang theory being displaced by a Mother of All Blackhole spewing galaxies (or star matters).

Valgrim 4y ago
Is that thr same as the so-called black hole cosmology theory?
- egberts1 4y ago
  yeah Like Galileo, individual scientists do not matter. https://bigthink.com/hard-science/black-holes-prove-the-universe-keeps-exploding-claims-physicist/ https://bigthink.com/hard-science/black-holes-prove-the-univ...