[HN Gopher] I think faster than light travel is possible
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I think faster than light travel is possible
Author : bilsbie
Score : 72 points
Date : 2023-04-09 21:02 UTC (1 hours ago)
(HTM) web link (backreaction.blogspot.com)
(TXT) w3m dump (backreaction.blogspot.com)
| blindriver wrote:
| 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.
| mr_mitm wrote:
| 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 wrote:
| Uhh... Whut? Special relativity absolutely allows CTCs. It
| actually provides an exact prescription of how to do it - move
| faster than light.
| Zigurd wrote:
| 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 wrote:
| 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 wrote:
| 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
| mr_mitm wrote:
| 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.)
| macawfish wrote:
| [flagged]
| ash_rahman wrote:
| [flagged]
| throwawaymaths wrote:
| 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.
| rcme wrote:
| Law of excluded middle. The two statements are equivalent.
| lll-o-lll wrote:
| 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 wrote:
| 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
| lll-o-lll wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| blindriver wrote:
| Give her a break. Unfortunately the way search is these days,
| you need to use clickbait titles even if your content is
| great. So it's part and parcel with our times and how the
| Algorithm works, unfortunately.
| dmix wrote:
| 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 wrote:
| 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
| blindriver wrote:
| Professional Youtuber != Full-time Youtuber.
| JeremyBanks wrote:
| Is it clickbait? It's slightly provocative but the content
| seems to live up to it.
|
| She's deconstructing absolutist nonsense into something less
| absolutist. It's almost anti-clickbait.
| mr_mitm wrote:
| She also seems to really enjoy taking contrarian views, which
| resonates with a lot of people who distrust "the scientific
| establishment" or who "want to believe".
| decremental wrote:
| It must be so upsetting that people exist who don't agree
| with the prevailing narrative. The brightest minds don't
| belong to people who lick their finger to see which way the
| wind is blowing today.
| kelnos wrote:
| This is the thing that bothers me about her videos, though.
| Certainly established science should be challenged when
| there is the potential that something isn't quite right.
| (Science itself may be "perfect", but it is performed and
| chronicled by flawed, biased humans.)
|
| But I feel like she takes a contrarian view just for the
| sake of being contrarian, so it's hard to tell which of her
| ideas actually have merit, and which simply exist to
| challenge the status quo, even when the status quo is
| conclusively proven.
|
| Edit: that said, I really do want to believe this! The
| speed of light being an absolute limit to how fast we can
| travel (or even communicate), means most of the universe
| (even most of the galaxy) will be forever out of reach to
| us. And that's kinda depressing. Unfortunately, physics
| doesn't care if I'm sad or happy about it.
|
| Edit2: on the other hand (I wrote the above after only
| having watched have the video, shame on me), I do find
| compelling her idea that some mathematical constructs (like
| special relativity) inherently cannot fully describe
| reality (in SR's case, SR doesn't include gravity). So
| saying "special relativity says FTL travel causes time
| paradoxes and thus cannot be possible" may be true, but
| since SR can't fully describe reality (hell, neither can
| GR), maybe it just doesn't matter. But who knows,
| IANAPhysicist, etc.
| misnome wrote:
| Most of her arguments seem to end up along "everything
| currently funded should be canceled and what I am doing
| should be funded instead", which I find extremely hard to
| take seriously.
|
| That, or yes - clickbait contrarian. This seems to get a
| lot of loud followers though.
| causality0 wrote:
| 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.
| rbanffy wrote:
| It might be the most impractical thing ever done, but it's also
| very useful if feasible.
| ben_w wrote:
| > 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.
| sunaurus wrote:
| 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.
| arnoldb0620 wrote:
| I am just a lay person but I tend to think about FTL travel in
| terms of traveling faster than the speed of sound. There is a
| sight dimension in which we can see the object before we hear
| it. Is there another dimension that we can observe the object
| traveling FTL?
| maxbond wrote:
| You can think of the speed of light as the speed at which
| causes produce effects. In the same way that the speed of
| sound[1] is the speed at which one air molecule can tell
| another air molecule that it's been been moved, the speed of
| light is the speed at which one piece of spacetime can tell
| another piece of spacetime that something has happened to it.
| Light just happens to move as fast as it as possible to move,
| the speed of light might be better described as the speed of
| causality.
|
| This speed defines the "happens before" relation in spacetime,
| like a Lamport clock defines the "happens before" relation in a
| distributed system. Event A "happens before" event B if all the
| information about B was known when A happened. Otherwise B
| happens at the same time or later than A.
|
| If you can travel faster than light (faster than causality),
| there's nothing stopping you from constructing a scenario where
| A happens before B and B happens before A. And that's what it
| means to violate causality.
|
| [1] To head off a potential confusion, note that while a jet
| may be able to move faster than sound, the sound of that jet
| passing by does not.
| ben_w wrote:
| Ok, so, at 14:45 in the video she shows some spacetime
| diagrams. The "normal" interpretation is that the distortions
| shown, including the event-ordering flip she shows, represent
| reality. Relativistic motion is _actual_ time dilation and not
| merely your perception of someone else 's motion. This is
| backed up by evidence in a lot of extreme cases.
|
| I don't have the skills to know if one is really "allowed" to
| say that there exists some frame of reference that is preferred
| or if that breaks something else, but _I think_ that any such
| frame where time must always go forwards would do what she 's
| saying here.
|
| Possibly.
|
| Unfortunately, I know this is an area where not only does my
| intuition often fail me, but where I can easily have the wool
| pulled over my eyes with plausible sounding but erroneous
| maths.
| sigmoid10 wrote:
| >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.
|
| There seems to be a general misunderstanding here. A different
| order of events can easily be observed without FTL, but only
| for events outside of our own light-cone. If we could observe
| events within our own light-cone without causal ordering, they
| could still affect us and thus would easily create paradoxes.
| However, if you are limited by the speed of light, this can't
| happen.
| wiml wrote:
| It's because "simultaneous" is relative in the same way that
| "in the same place" is relative. You can bounce a ball against
| the same spot repeatedly, but if you're on an airplane and
| another observer isn't, the places the ball hits are separated
| by a large distance in their reference frame.
|
| Most concretely, the FTL-breaks-causality conclusion comes
| from: _If_ special relativity holds (it does), _and_ you have
| FTL travel, _and_ there is no universal privileged frame of
| reference affecting your FTL drive, _then_ it 's possible to
| get back to your starting point before you leave by making
| multiple FTL hops. You have to be able to make the two hops in
| different reference frames, that is, you need to do a bit of
| conventional acceleration between hop 1 and hop 2.
|
| From everything we know about the universe it seems unlikely
| that there's a special preferred frame out there, but if for
| example you're developing a hard-science-fiction setting and
| want FTL without causality violations, you can throw in that
| background detail to keep the physicists happy.
|
| > it would be possible to OBSERVE events in the wrong order
|
| True, but of course that's possible even in normal earth-bound
| newtonian physics. All of the discussions about relativity
| assume that all the observers are taking speed-of-light delays
| into account when they're observing.
| neurobashing wrote:
| One of the Xeelee Sequence novels deals with this problem
| specifically: a pilot in an FTL space fighter uses multiple
| hops to defeat an enemy, and ends up back before he left.
| It's a Xeelee Sequence book, grimdark of grimdark, so
| hilarity does not ensue.
| mr_mitm wrote:
| There is nothing intuitive about special relativity. If you
| want to understand SR (or GR or QM), you must throw intuition
| out the window and strictly follow the rules of the theory.
|
| The best explanation for why FTL breaks causality that I have
| seen is the tachyonic antitelephone:
| https://en.wikipedia.org/wiki/Tachyonic_antitelephone
|
| Drawing a bunch of spacetime diagrams might help as well.
| maxerickson wrote:
| 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 wrote:
| 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.
| superposeur wrote:
| 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 wrote:
| [dead]
| maxbond wrote:
| Can we switch the link to 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 wrote:
| [flagged]
| maxbond wrote:
| 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 wrote:
| 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.
| tempestn wrote:
| How does that pertain to using the more relevant link?
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