[HN Gopher] Warp Drive News
___________________________________________________________________
Warp Drive News
Author : mellosouls
Score : 126 points
Date : 2020-11-27 15:58 UTC (7 hours ago)
(HTM) web link (backreaction.blogspot.com)
(TXT) w3m dump (backreaction.blogspot.com)
| sitkack wrote:
| Ok I have a question kinda related about bubbles traveling faster
| through a medium.
|
| If objects underwater can supercavitate, can objects in the
| atmosphere also supercavitate and can we have objects orbiting
| the earth inside the atmosphere?
| robbmorganf wrote:
| That's an interesting question. Supercavitating torpedoes take
| advantage of two effects (a) gas typically is much less viscous
| than liquid, which reduces drag and (b) if you reduce the
| pressure enough, liquid turns into gas.
|
| In the atmosphere, you're already in a gas, so there's not an
| obvious other state of matter that would be advantageous.
| Furthermore, reducing pressue would certainly reduce drag, but
| not by orders of magnitude like a phase transition.
|
| But in the spirit of 'yes, and': if you reduced pressure near
| the skin by A LOT (near vacuum) you might see a dramatically
| lower drag. Maybe that could be accomplished by ionising the
| incoming air and then electrostatically repelling it? Who
| knows. It's fun to speculate though.
| cfv wrote:
| So, the biggest question I have about all this eminently
| theoretical physics video thing is, has anyone ever managed to
| experimentally demonstrate you _can_ __voluntarily__ bend the
| brane our reality resides on by _any_ measurable amount, and also
| demonstrate this causes an actual translation in 3d space? At
| all? Ever?
|
| Or are we conjecturing what would happen if this was even
| slightly viable?
|
| We've only very recently managed to experimentally demonstrate
| that unimaginably huge cataclismic events can make this happen,
| but, has anyone ever built some device that can make a crease of
| _any_ significance at all in reality, and do so at will?
| generalizations wrote:
| https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field...
| cfv wrote:
| So... no?
| generalizations wrote:
| My reading is, 'needs better measuring tools'.
| whimsicalism wrote:
| I'm tired of all of these Sabine posts, can we get someone else?
|
| e: I'm curious what the opinion of professional physicists would
| be.
| segfaultbuserr wrote:
| https://news.ycombinator.com/newsguidelines.html
|
| > When disagreeing, please reply to the argument instead of
| calling names.
|
| > Please don't post shallow dismissals, especially of other
| people's work. A good critical comment teaches us something.
|
| > Please don't comment about the voting on comments. It never
| does any good, and it makes boring reading.
| tasty_freeze wrote:
| Want to know why you are being downvoted?
|
| 1 - Your comment isn't about content of the article. I don't
| use apple hardware or software. There are tons of apple posts,
| especially about the M1. How would it work out if all the
| people who aren't part of the apple ecosystem hit every apple
| story with a "Sheesh, not another apple article! Can't we get
| something more interesting?"
|
| 2 - You are free to submit things you think are interesting. Be
| the change you want to see, etc.
|
| 3 - People who whine about being downvoted tend to get more
| downvotes
| whimsicalism wrote:
| > Your comment isn't about content of the article.
|
| It is a commentary on the article. Having read the article, I
| think regardless of Sabine's credentials, she has gone the
| wrong path in terms of science communication. Apple is a
| topic, Sabine is an author. It's the physics equivalent of
| asking for a source other than the Daily Mail.
|
| > People who whine about being downvoted
|
| I'm legitimately curious about the opinion of professional
| physics. I've worked with quite a few professional AMO
| physicists and the opinions of Sabine's content there are
| very low.
| segfaultbuserr wrote:
| You won't be downvoted if you've said this in the first
| place.
| WarOnPrivacy wrote:
| Downvoting is reasonably considered peer punishment. To
| infer it has value as a (other than last ditch) teaching
| tool, seems like poor judgment to me. There are better
| options to apply to people who want to learn - which is
| mostly everyone.
|
| edit: I can appreciate the snark value, however.
| noch wrote:
| > I've worked with quite a few professional AMO physicists
| and the opinions of Sabine's content there are very low.
|
| Think for yourself. Learn the math or physics you need and
| try to form your own conclusions. All books are free. This
| is the great responsibility for anyone alive in our time
| and it's hard, thankless work: to think from first
| principles and to do our own homework. _There is no way
| around it_. Needing other people 's opinions before
| rigorously forming our own quickly devolves into talking
| about people and other people's opinions instead of talking
| about fundamental ideas.
|
| Unless of course one is more interested in talking about
| opinions and personalities than understanding ideas. If her
| "content" is poor in someone's eyes, the question that
| remains relevant is: what are the ideas and their
| principles?
| davrosthedalek wrote:
| Sorry, but this doesn't scale. You have finite time
| available, you cannot be a master of everything, and
| recognizing this and asking for the opinions of those who
| are, is the right way to handle that.
| noch wrote:
| > Sorry, but this doesn't scale.
|
| As my cello teacher said: the effort is the thing. You
| probably won't become a master but you have to make the
| effort. _The effort is all_.
|
| Importantly, everything valuable that is known was once
| unknown by everybody, including masters. If we don't make
| the effort, there's no chance of going beyond frontiers.
| We are left discussing what so-and-so said they think
| about what so-and-so thinks about what so-and-so wrote
| about a paper and the author's personality.
| qayxc wrote:
| > As my cello teacher said: the effort is the thing. You
| probably won't become a master but you have to make the
| effort. The effort is all.
|
| Stick with playing the cello then.
|
| > Importantly, everything valuable that is known was once
| unknown by everybody, including masters.
|
| We as a species are _way_ beyond the point that laymen -
| no matter their intellectual capacity - can acquire
| detailed knowledge about every special topic in even just
| a single scientific area.
|
| This isn't as simple as music theory or perfecting motor
| functions by means of practising. Just to give you an
| idea of the scale we're talking here:
|
| The journal "General Relativity and Gravity" [1] alone
| published 167 papers in 2019.
|
| _Yesterday_ (!) alone, 20 papers were announced on
| arxiv.org [2]
|
| So assuming you already know GR by heart, you'd need to
| spend every waking minute of your existence just reading
| up on what's currently being discussed within the
| community. This leaves absolutely no time for reflection
| on and understanding the material, let alone working on
| original ideas.
|
| You are delusional if you think that 200 years of modern
| mathematics, physics and astronomy can be mastered by a
| single person, let alone an _average_ person, who rarely
| has the mental capacity to even understand most of the
| material en detail.
|
| [1] https://link.springer.com/journal/10714/volumes-and-
| issues
|
| [2] https://arxiv.org/list/gr-qc/new
| noch wrote:
| > You are delusional if you think that 200 years of
| modern mathematics, physics and astronomy can be mastered
| by a single person, let alone an average person, who
| rarely has the mental capacity to even understand most of
| the material en detail.
|
| _You_ are delusional if you imagine I said you should
| master everything. In fact, I said you should make the
| effort. Recall, John Nash said that in graduate school he
| had to reinvent 300 years of mathematics for himself? And
| just how many books did Witten say he studied in a year
| in graduate school on his own?
|
| Try to calm down and question your assumptions. I'm not
| your enemy.
|
| Trying to understand stuff before asking for an opinion
| is a habit. If you don't practice it, you can't do it,
| and you shouldn't be surprised if you instead believe
| that the default should instead be relying on others who
| practice the habit.
|
| Importantly, the habit of doing your own homework is
| actually a muscle: if you don't strengthen it, it will
| atrophy or never develop. The stronger it is, the faster
| working through physics and mathematics and chemistry
| papers becomes. Perhaps we can do better than our masters
| from the Renaissance if we try?
|
| > Stick with playing the cello then
|
| Thanks! That's kind of you to say. It's a struggle but
| I'm getting there.
|
| > This isn't as simple as music theory or perfecting
| motor functions by means of practising.
|
| You think music is simple? You are totally trolling me. I
| like your sense of humour.
| whimsicalism wrote:
| > Think for yourself. Learn the math or physics you need
| and try to form your own conclusions
|
| I studied physics at Harvard, I'm hardly _unstudied_ in
| the area, but yes, I 'll be the first to admit that I
| don't know QFT or really anything beyond basic QM and
| general relativity.
|
| > This is the great responsibility for anyone alive in
| our time and it's hard, thankless work: to think from
| first principles and to do our own homework
|
| Absurd. I do not need to learn advanced GR/QFT from first
| principles to know enough to comment on Sabine, nor do I
| need to verify every principle from first axioms in order
| to come to conclusions.
|
| Humans _have_ to learn to rely on trusting the judgements
| of others in order to make scientific advancement.
| Physicists can 't spend their whole life validating that
| basic mathematical axioms are true, they have to _trust_
| the body of academic mathematicians who have done that
| work. I reject the entire premise of your comment.
| noch wrote:
| > Humans have to learn to rely on trusting the judgements
| of others in order to make scientific advancement.
|
| Trust but verify. Better yet, trust your effort first,
| then trust others later.
|
| > I studied physics at Harvard,
|
| Wow. Harvard!
|
| > Absurd. I do not need to learn advanced GR/QFT from
| first principles to know enough to comment on Sabine, nor
| do I need to verify every principle from first axioms in
| order to come to conclusions
|
| Consider if all the people whose opinions you want
| studied at Harvard like you and also believe the
| statement you made. Will the blind lead the blind?
| blincoln wrote:
| I'm also very curious about the opinions of other
| physicists.
|
| Dr. Hossenfelder seems to have a lengthy, strong background
| in physics. On the other hand, every time I read one of her
| transcripts, I see something along the lines of the
| "superluminal travel doesn't necessarily result in the
| possibility of causality violations" claim in this one.
| Every modern text I've read about physics has indicated
| that superluminal travel (or signaling) inexorably means
| that causality can be violated, unless Einstein was missing
| something.
|
| In the last one I read, there were claims about Hawking
| radiation and virtual particles that also seemed to
| contradict everything I've read. Now, it may be the case
| that those texts really are simplified down and one learns
| what's really going on in some advanced physics course, but
| twice in as many transcripts is a red flag for me. It's not
| at the Dr. Salvatore Cezar Pais level yet, but usually
| people who consistently claim that all of the experts are
| wrong are themselves wrong, and so I'd like to see some
| non-self-referential confirmation.
| wwarner wrote:
| In this particular post, she referenced causality in one
| sentence
|
| > Neither does this faster-than light travel necessarily
| lead to causality paradoxes.
|
| I take this to mean that if you could travel FTL to a
| very distant place that you could never get to otherwise,
| like say whatever universe there is that is farther away
| than light can travel in age of the universe, then there
| isn't a causality problem. Which isn't controversial. I'm
| pretty sure there are other FTL scenarios in which there
| is no paradox.
| whatshisface wrote:
| Hossenfelder doesn't claim that all the experts are
| wrong. She has a reputation as a maverick because she
| published a book claiming that some experts were wasting
| time. In fact I think a term she used to describe it was,
| "not even wrong."
| [deleted]
| tasty_freeze wrote:
| > > Your comment isn't about content of the article. > It
| is a commentary on the article.
|
| I stand by what I said: you weren't commenting on the
| article. You were commenting about the author of the
| article, and that you were tired of seeing news about her.
| WarOnPrivacy wrote:
| Sorry for the downvotes.
|
| I'm a good audience for her writeup - someone who hasn't deep-
| dived into FTL for decades.
|
| Maybe it helps I'm not at all familiar with Sabine.
| [deleted]
| Stierlitz wrote:
| In the latest Star Trek, the starship Discovery runs on spores
| harvested from shrooms grown onboard. Despite being set in the
| Captain Pike era, no one ever noticed this up to then :]
| LockAndLol wrote:
| > Bobrick and Martire explain that if you want superluminal
| motion, you need negative energy densities. If you want
| acceleration, you need to feed energy and momentum into the
| system. And the only reason the Alcubierre Drive moves faster
| than the speed of light is that one simply assumed it does.
| Suddenly it all makes sense!
|
| Uh... what?
| ickelbawd wrote:
| They're ultimately saying the Alcubierre Drive can't go
| superluminal speeds because negative energy is not real, but it
| will work just fine if you go slower than the speed of light.
| scarygliders wrote:
| I'm wondering if part of the problem with trying to come up with
| technology which allows us to propel ourselves vast distances
| "faster than the speed of light", is to do with how we
| abstract/describe the problem (and the proposed solution) in
| language.
|
| For example; instead of saying "faster than the speed of light",
| would the problem not be better described using "faster than the
| speed of causality" ?
|
| After all, isn't c really just the speed of Causality in a
| vacuum? (i.e. the time it takes for a beam of light from a source
| to be detected at, say, a distance of 500,000 kilometres, is
| basically the rate at which Causality allows that light to get
| from the emitter to the detector.)
|
| And isn't the speed of Causality, basically like some kind of
| inertia-like quality of spacetime? (Apologies in advance - I'm
| trying to describe what's in my head as best I can using...
| language ;) ) For example - the speed of "light"/Causality
| through water is slower than the speed of "light"/Causality
| through a vacuum.
|
| (And mea culpa - I am a layman, trying to make sense of all this
| in as best a way I can. I'm not sure if what I wrote makes any
| kind of sense (it does in my head))
| whimsicalism wrote:
| Your claim is that we've had trouble coming up with technology
| going FTL because physicists forget that the speed of light is
| the same as the speed of causality?
|
| I'm probably misunderstanding what you're saying.
| scarygliders wrote:
| It's not really a claim, it was a pondering - a thinking out
| aloud.
|
| And it's more to do with the use of language to describe the
| problem (how to break the "light barrier") than forgetting
| something. And the use of language in abstracting/describing
| solutions to it.
| krapp wrote:
| That the speed of light is invariant in a vacuum is a
| result of Einstein's theory of special relativity[0,1] and
| Maxwell's field equations[2]. These may be described
| generally with language like "speed of light" but they were
| described specifically and tested using math and science.
| And at this point, these are probably the most thoroughly
| tested and proven principles in science, since they
| underpin everything from cosmology to quantum mechanics to
| chemistry (and by extension biology) and a lot of our
| modern technology such as satellites (which have to take
| special relativity into account) and microchip design, for
| which quantum effects are relevant.
|
| [0]https://en.wikipedia.org/wiki/Special_relativity
|
| [1]https://en.wikipedia.org/wiki/Speed_of_light
|
| [2]https://web.pa.msu.edu/courses/2000fall/phy232/lectures/
| emwa...
| tzs wrote:
| There's an episode of PBS Space Time about this, "The Speed of
| Light is NOT About Light" [1], which comes pretty close to
| making the same points you are making.
|
| It might be useful to watch this earlier episode, "Are Space
| and Time an Illusion?" [2], first.
|
| There is a later episode (or maybe a couple of them) that go
| into how interactions with the Higgs field make it so things
| with mass travel slowed than the speed of causality.
|
| To tie back to the warp drive news, they have an episode that
| would be a good place to start on warp drives, "Is The
| Alcubierre Warp Drive Possible?" [3]. There's also
| "Superluminal Time Travel + Time Warp Challenge Answer" [4],
| and "Will Wormholes Allow Fast Interstellar Travel?" [5]. A
| non-warp unknown physics drive that comes up a lot also got an
| episode, "The EM Drive: Fact or Fantasy?" [6].
|
| There is at least one episode covering interstellar travel
| without using any unknown physics, "5 REAL Possibilities for
| Interstellar Travel" [7].
|
| The scope of the series is basically anything vaguely connected
| to astronomy, cosmology, and quantum mechanics, and the
| episodes are all pretty short (5-12 minutes), so it is a great
| thing to watch when you've got a short wait for something.
|
| Here's the series home page [8], and their YouTube channel [9].
| Also on the PBS streaming app, for those who like to get their
| physics on their big screen TVs.
|
| [1] https://www.youtube.com/watch?v=msVuCEs8Ydo
|
| [2] https://www.youtube.com/watch?v=YycAzdtUIko
|
| [3] https://www.youtube.com/watch?v=94ed4v_T6YM
|
| [4] https://www.youtube.com/watch?v=HUMGc8hEkpc
|
| [5] https://www.youtube.com/watch?v=ldVDM-v5uz0
|
| [6] https://www.youtube.com/watch?v=hqoo_4wSkdg
|
| [7] https://www.youtube.com/watch?v=EzZGPCyrpSU
|
| [8] https://www.pbs.org/show/pbs-space-time/
|
| [9] https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g
| Misdicorl wrote:
| Separating the terms/ideas may actually be useful to address a
| common misconception you illustrate here. Light does change
| speed in water, but causality does not
| whimsicalism wrote:
| > Light does change speed in water, but causality does not
|
| Well, the speed that the photons travel between the water
| atoms is still c.
| scarygliders wrote:
| The concept I have in my head if I can describe it well
| enough, is that the speed of Causality _is_ different in
| water, than it is in a vacuum.
|
| An underwater explosion travels slower in water than it does
| in a vacuum. That's not just to do with the coefficient of
| friction of the water. The light from the explosion will take
| longer to reach you than it would if you and the explosion
| were in a vacuum.
|
| Which leads me to another thought - does that mean that the
| _matter_ of water is basically just another form of
| spacetime, in which the speed of Causality is different from
| the speed of Causality in spacetime in a vacuum?
| poopchute wrote:
| Gravity travels at the speed of Causality, and that isn't
| changed in water
| Filligree wrote:
| Nah.
|
| The speed of light is slower in water, yes, which is why
| Cherenkov radiation exists -- that's basically the photon
| equivalent of a supersonic shockwave. The speed of
| causality doesn't change, and it's easy to demonstrate that
| by throwing particles through it at superluminal speeds;
| nuclear reactors do it all day long.
| purple-again wrote:
| I'm as layman as you here but I assume it comes from the line
| of thought "just because light is contained to only go that
| fast doesn't mean matter has to be constrained to only go that
| fast."
|
| It's a natural extension of knowing that humans can't fly. We
| need only look up to see that constraint didn't hold up to the
| rest of time nearly as well as contemporary humans assumed it
| would.
|
| How do we know that some immutable property of space/time
| causes light to travel at the speed it does rather than the
| other way around where some immutable property of light causes
| it to be incapable of traveling any faster (the old strap wings
| to a human and look now it can fly; so strap X to light and
| look now it can go faster to!)
|
| Again, the extent of my knowledge in this space is from Star
| Trek not science so please be gentle with my clear level of
| ignorance.
| scarygliders wrote:
| > "just because light is contained to only go that fast
| doesn't mean matter has to be constrained to only go that
| fast."
|
| See, I'd try and frame it as "just because Causality
| constrains light to only go that fast..." and try to think
| what Causality is. And if Causality is a property of
| spacetime then how would I go about building a "Causality
| Engine" in order to alter spacetime in such a way that the
| speed of Causality can be broken ;)
|
| My mind is warped - pun intended.
| rytill wrote:
| Isn't the only reason the speed of causality is the speed
| of light because light is the fastest thing? And if you
| were able to go faster than it, that new speed would be the
| speed of causality?
| marcosdumay wrote:
| There is an interesting property of the speed of
| causality, that it is fixed independently of the observer
| (as in, any observer will measure the same speed).
|
| Our mechanics allow only one such speed, and if you try
| to use one that doesn't have this property for causality,
| you'll get all kinds of paradoxes.
|
| But it's probably something that can be solved. All said,
| the reason we assume causality moves at that speed is
| because it agrees with the experiments.
| jodrellblank wrote:
| As a blind-leading-the-blind layman answer, if you shove a
| car forwards it will move slowly (ignore air/tyre resistance
| and such).
|
| The same strength shove hardly moves an artic truck, it
| wobbles a Ford F-150, it pushes a sedan, it rolls a small
| sports car, without air resistance and axel friction, it's
| only the mass which resists your shoving and determines the
| speed. and you can imagine waving a magic wand over the car
| to lower its mass then the same shove pushes it faster and
| faster. At the mass of a ball bearing the car pings away.
| Like a tennis racket swing can't move a car but can move a
| tennis ball at 100mph.
|
| Until there is no mass left, at that point any shove and it
| skitters away enormously fast. As mass drops the shove pushes
| it faster. As mass goes to zero, it goes "infinitely" fast.
|
| There isn't any mass left to remove, so the only way you can
| speed it up from here is to push harder instead... but now as
| soon as you touch it at all, at any pressure, it skitters
| away and you aren't touching it anymore so you can't push -
| damnit. The first inkling whisker of a skin cell touching the
| car and it's off, the time it takes to "wind up" your shove
| power is too slow, the massless car is 300,000m away in a
| thousandth of a second. You can't keep your hand on it, let
| alone go faster than it to provide more pushing force!
|
| In fact the only way you can move your hand fast enough to
| keep up with it, so you can keep touching it long enough to
| give it more push, is if your hand also has no mass. And now
| your massless hand can't be pushed by your real muscles for
| the same reason, once stuff has no mass you can't get a grip
| on it. So pushing harder is out.
|
| Maybe you can push it faster in a non-mechanical way like
| electromagnetically? Ok, you send some magnetic waves after
| it. Photons. They have no mass, so they travel at the same
| speed as well. They can never catch the car to push it. Like
| a game of tag where you run behind someone waving your arm at
| them but never quite able to touch them, you sure can't push
| them harder if you can't ever quite touch them. Nothing can
| catch up to provide more push.
|
| So it can't go faster than this "infinite" speed.
|
| > _How do we know that some immutable property of space /time
| causes light to travel at the speed it does rather than the
| other way around where some immutable property of light
| causes it to be incapable of traveling any faster_
|
| Because the speed isn't how fast light goes, it's how fast
| spacetime lets massless things go through it and light
| happens to be a massless thing. If mass is what resists
| movement, and you take all of it away, there isn't any way to
| go faster because you can't take more mass away than all of
| it.
|
| (Wish I'd written this with whacking tennis racket on a car,
| bowling ball, baseball, ball bearing...) seems easier to
| imagine.
| mybandisbetter wrote:
| I've often thought that "the speed of causality" would be a
| much better name for it. Interesting you landed on the same.
| Animats wrote:
| _" Note: This paper has not appeared yet. I will post a link here
| once I have a reference."_
| WJW wrote:
| I'm very mystified why this is called "news" about warp drives.
| The article is about an as-yet unpublished and un-peer reviewed
| paper that describes a general type of spacetime configuration
| which _might_ go faster than the speed of light. That is cool,
| but not really something we didn't have before.
|
| Also, any article that ends with a phrase like "while it may look
| now like you can't do superluminal warp drives, this is only
| correct if General Relativity is correct" does not bode well for
| practical applications of the subject matter. There is also the
| logical fallacy that it might be the case that GR is incorrect
| and you still can't do superluminal speeds.
| paulpauper wrote:
| Also her explanation of how general relativity works, the
| equations specifically, is too simplified and not even
| conceptually correct to be of any use to the reader who wants
| to understand this deeper . The right hand side is the
| parametric representation in matrix form of the manifold used.
| The 'R' is the curvature tensor, which is a in terms of the
| metric and its derivatives of the entries. Because there are 4
| dimensions, a 4x4 metric tensor is used to describe the
| manifold, and because it is symmetric, there are 10 unique
| entries and hence 10 equations. These entries are not integers
| but are parametric equations themselves.
| simonh wrote:
| I thought she very clearly explained how this is different from
| warp drive concepts before, and why this is more interesting.
| Sure, you could disagree with her on that, but your post reads
| as if you're not even aware she addressed those points at all.
| hinkley wrote:
| We seem to systematically forget that the "shockwave problem"
| for FTL or even high fractional C travel is that all the light
| of the stars in front of you is now gamma radiation due to red
| shifting, and every particle you encounter behaves like cosmic
| rays. We will cook ourselves and our ships will turn to dust.
|
| A warp drive that lets your local frame feel like .1c while you
| are actually traveling at .3c would still be a civilization-
| altering development.
| Supermancho wrote:
| > We seem to systematically forget that the "shockwave
| problem"
|
| It's not clear that this method of manipulating space-time
| would create a shockwave (I would be surprised if it didn't
| on start/stop) or would interact with matter differently from
| subliminal travel in transit.
| MertsA wrote:
| Just about all "practical" warp drives encase the "ship"
| inside of a miniscule bubble in regular space. The amount of
| photons and particles that actually hit that bubble and enter
| the expanded space within is absolutely tiny. The energy
| requirements to do otherwise are just flat out ridiculous. If
| humanity ever develops a practical warp drive it'll have to
| use this "bubble" approach one way or another or there's
| something seriously wrong with the theory of general
| relativity.
| imglorp wrote:
| Technically the proposed drive is not moving within spacetime
| but instead is causing a spacetime bubble around the ship to
| compress and expand. So redshift might be zero inside? It's
| about as speculative as the negative mass required.
| hinkley wrote:
| Yeah that's what I meant by local frame; your velocity
| inside of the "warp bubble" is much less relativistic in
| nature and thus less problematic.
| whatshisface wrote:
| Breaking the speed of light barrier is a more fundamentally
| difficult problem than shielding from radiation, and that's
| an understatement.
| hinkley wrote:
| I don't agree. Particularly, shielding is probabilistic,
| isn't it? So the higher the flux the more shielding you
| need. More shielding makes it harder to accelerate, and now
| you're dealing with the rocket equation again. Your target
| (average) speed requires a certain amount of shielding, and
| we may have no propulsion that can achieve that speed on
| any trip worth taking. Or due to the rocket equation, ever.
| whatshisface wrote:
| You're comparing an engineering decision (to use mass for
| shielding instead of some kind of clever redirection
| technique) plus another engineering decision (to use a
| propulsion technique subject to the rocket equation),
| against a direct consequence of special relativity.
| alisonkisk wrote:
| General Relativity, not Special Relativity.
|
| Special Relativity is about velocity, not bending
| spactime.
| whatshisface wrote:
| Special relativity is sufficient to introduce the
| paradoxes associated with superluminal travel.
| alisonkisk wrote:
| The topic of the new paper and this comment thread is
| primarily subliminal warp, not superluminal warp.
| alisonkisk wrote:
| It's news because it's a new paper. Even if the paper might be
| wrong, it's still news.
|
| Regarding practicality, you may have missed the thesis, which
| is that warp drives are more practical than previously thought,
| because the theory allows subliminal warp drives at finite
| energy, not only superluminal warp drives at unphysical
| negative energy.
|
| The part about GR is just the stretch part. It's obvious what
| she means about GR, that our current arguments against
| superluminal drives are based on General Relativity.
| dnautics wrote:
| Sabine is very careful about how she defines warp drives in the
| beginning of the video. A warp drive that is not superluminal
| is still interesting for other reasons (all reactionless drives
| are kind of interesting). Also importantly the paper suggests
| specific mathematical properties of the geometry; namely that
| they should be flatter in the direction of motion. That is not
| at all intuitive to me, and certainly not the aesthetics of
| space ship design in most sci-fi.
| stagas wrote:
| A flying saucer is quite flat though.
| dnautics wrote:
| wow, I didn't think of that... it's interesting that a lot
| (but not all) of sf has flying saucers moving in a
| "horizontal" direction" where the GR solution suggests
| moving in the "vertical" direction, which some science
| fiction does do.
| smegcicle wrote:
| secondary propulsion system for maneuvering out of warp-
| and how goofy would it be to walk around in a vertically
| standing ship in gravity?
| galaxyLogic wrote:
| Fascinating. After all these years only now we know why
| Flying Saucers are saucer-shaped.
| marcosdumay wrote:
| If they are moving on what we imagine as "up" or "down"
| directions. If it's moving on any direction people actually
| expect them to move, they are not very flat.
| enoreyes wrote:
| Funny enough, in the Navy's released footage of the "tic-
| tac" [1] this appears to be exactly what it does - it
| orients it's flat side towards the direction of intended
| movement then propels forward at (seemingly impossible)
| speeds. I'm not sure I have an opinion yet about if this
| tech is real, but it'd be interesting to hear (if these
| videos are fake) whether or not research went into
| "optimal" shape for breakthrough propulsion techniques
| which were then reproduced in a video.
|
| https://www.navair.navy.mil/foia/documents
| gruez wrote:
| I'm fairly sure these videos were debunked as being
| trickery/illusion with parallax, rather than objects
| traveling at impossible speeds.
| generalizations wrote:
| I was pretty sure (from reading on hn) that the videos
| were validated (that the debunking was debunked...).
| gruez wrote:
| Source? Here's mine:
| https://www.youtube.com/watch?v=Q7jcBGLIpus
| jml7c5 wrote:
| The navy confirmed they were real recordings, but AFAIK
| did not validate anything about the contents of the
| recordings.
| enoreyes wrote:
| I think (If you're referring to Mick West's explanation)
| that's actually a pretty convincing argument for the "Go
| Fast" video. I'm not as convinced the Gimbal video can be
| explained as easily. Combined with witness testimony and
| the Pentagon explicitly claiming it's unidentified, I
| would love to hear a more convincing argument than "it's
| a plane and exhaust jet that the Navy's state of the art
| sensors, pilots, etc. misidentified"
| jml7c5 wrote:
| What is unconvincing about the gimbal explanation?
| infradig wrote:
| The Pentagon (or Navy I think you mean) has never made
| any statement on the content of the videos other than
| validating that they are real videos (by releasing them).
| kreeben wrote:
| Debunked, by whom? Where is a trustworthy place I read
| about this?
| gruez wrote:
| I posted a youtube link in a sibling comment.
| layoutIfNeeded wrote:
| By _skeptics_!
| lumost wrote:
| I didn't read the paper, but Sabine's summary specifically
| notes that the drive requires energy and momentum to
| accelerate. While the mechanism behind providing momentum
| could be varied, some form of reaction drive would almost
| certainly be required.
| JoeOfTexas wrote:
| Ok, so Warp Drives have many technological hurdles to accomplish,
| but currently all assumptions are on expansion and compression of
| space-time at faster than light speeds.
|
| Let's say we want to travel in 1 hour to the nearest star 4 light
| years away. That would require compressing roughly 6.5 billion
| miles/second of spacetime into this bubble!
|
| All matter in those 6.5 billion miles will be sucked into your
| passenger area of the warp bubble and decompressed back to Earth
| spacetime. This would be a weapon of galactic destruction.
|
| But that's not the real issue, how exactly would we be able to
| warp spacetime faster than light at such large distances? The
| main engine would have to already be breaking the speed limit as
| part of its technical specification, which becomes a paradox,
| trying to use the solution as the foundation.
|
| Find an alternative solution to breaking the speed limit, and we
| can overcome the paradox.
| mabbo wrote:
| > All matter in those 6.5 billion miles will be sucked into
| your passenger area of the warp bubble and decompressed back to
| Earth spacetime.
|
| This presumes that we're doing the moving all in one big
| operation, doesn't it?
|
| What if each nanosecond, the warp bubble is moving forward by a
| small fraction, slipping through without imparting any momentum
| on the matter it passes by.
| simcop2387 wrote:
| It might not let you go FTL, but this would seem to imply that
| you could get going extremely fast without a reaction mass to
| perform the acceleration. That alone would make shorter
| interstellar trips like the one to proxima centauri feasible as
| far as time goes.
| m4rtink wrote:
| Well, any reactionless drive also hase massive implications
| for making mankind multiplanetary, even without taking any
| interstellar implications into account. You could move huge
| amounts of cargo and personnel just with a heavy electricity
| source (solar panels, nuclear reactor) but without having to
| care for the even more massive amounts of fuel otherwise
| needed!
|
| It would make interplanetary and orbital settlement not just
| possible but _easy_.
| nobodyandproud wrote:
| > It would make interplanetary and orbital settlement not
| just possible but easy
|
| I don't know about "easy", but it removes a logistical
| wall.
|
| I wonder if this sidesteps the time dilation effects of
| high speed travel.
| jandrese wrote:
| Any technology advanced enough to travel between solar system
| is advanced enough to destroy them. It's order of magnitude
| more difficult to make the trip than it is to blow up
| everything when you get there.
| blamestross wrote:
| Any reactionless drive might as well be FTL. The limit to
| traversing the universe isn't the speed of light it is the rocket
| equation. As long as you don't mind rather intense time dilation,
| you can get anywhere as fast as you want with enough fuel and
| ability to tolerate sustained acceleration. Remember: you can go
| any speed you can accelerate to, it is everything else that can't
| go faster than light.
| qayxc wrote:
| > Remember: you can go any speed you can accelerate to, it is
| everything else that can't go faster than light.
|
| You cannot accelerate masses to the speed of light, because if
| General Relativity holds, you'd require infinite energy to do
| so.
|
| In addition, every bit of radiation arriving from the direction
| of travel will be turned into high energy gamma radiation and
| cook you something fierce real quick; not to mention dust or
| tiny rocks that would release the energy equivalent of a
| thermonuclear explosion upon impact.
|
| Since these effects alone will create a practical upper limit
| to your interstellar travel speed, there's still a huge
| difference between FTL and reactionless drives. An FTL drive
| might get you to Proxima Centauri in a month, whereas even the
| most optimistic subluminal option will take at least a decade.
| blamestross wrote:
| > You cannot accelerate masses to the speed of light, because
| if General Relativity holds, you'd require infinite energy to
| do so.
|
| This is a common misconception. There is exactly 1 mass you
| can accelerate to any speed you want. YOU. Time dilation
| canceling out acceleration from the external perspective is
| why it looks like externally that it takes infinite energy to
| reach C. Light travels at C and thus experiences zero travel
| time. Things going slower than C will experience "some"
| travel time. Not 1 year per lightyear.
|
| On the ship it is locally Newtonian the entire way. Sure your
| destination and origin are doing weird gymnastics out the
| view screen, and the radiation is getting a bit energetic,
| but if you have the fuel and willingness to take Gs, you can
| travel any distance in any subjective amount of time. There
| exists a fuel budget (a lot) (at overwhelming Gs) to reach
| another star in 5 minutes.
|
| > In addition, every bit of radiation arriving from the
| direction of travel will be turned into high energy gamma
| radiation and cook you something fierce real quick; not to
| mention dust or tiny rocks that would release the energy
| equivalent of a thermonuclear explosion upon impact.
|
| This is a very real problem I offer no solution to other than
| adding shielding budget to the tyranny of the rocket
| equation. "warp drives" might offer a solution to this
| problem but all flavors of reactionless drives are currently
| SciFi. "If you have enough fuel" here likely means "a couple
| Jupiters worth of hydrogen that you fuse at perfect e=mc^2
| efficiency"
| jandrese wrote:
| The FTL drive might get you to Proxmia Centauri in a couple
| of seconds. It's purely fictional so why set artificial
| limits?
|
| You are right that the reactionless drive will be limited by
| the speed of light, but thanks to time dilation that 10 years
| might only feel like a couple of months to the passengers.
| It's cold comfort for their aging friends and relatives back
| home, but for the passengers it's not that much difference.
| progman32 wrote:
| Well, another implicit barrier is human lifetime. Though I
| suppose if we don't mind massive time dilation, we might not
| mind thousands of generations passing by during transit.
| xenadu02 wrote:
| That's not correct. If you could accelerate to a significant
| fraction of c then you can traverse the Milky Way well within
| a human lifetime from your point of view. Hundreds of
| thousands of years will pass on earth and your destination
| while you travel, but it's not a problem for the passengers.
| mrfusion wrote:
| What's the argument for warp drive not violating causality?
|
| (She mentions she explains it in another video but I couldn't
| find it.)
| jleahy wrote:
| The argument is that they're impossible, because they require
| negative energy (which not only doesn't exist but doesn't make
| sense), so it's fine.
|
| In the presence of negative energy you can form closed time-
| like curves in general relativity, which would violate
| causality, but these are not valid solutions because negative
| energy is not a thing.
|
| It's just like saying you can travel faster than the speed of
| light in special relativity, you just need imaginary mass (ie.
| m^2<0), but mass is unfortunately a real quantity rather than a
| complex quantity so you can't.
| mrfusion wrote:
| Isn't this artical saying you don't need negative energy?
| [deleted]
| hdhdurhdhdud wrote:
| " Bobrick and Martire show that for the Alcubiere drive you can
| decrease the amount of energy by seating passengers next to each
| other instead of behind each other, because the amount of energy
| required depends on the shape of the bubble. The flatter it is in
| the direction of travel, the less energy you need"
|
| I don't buy into the UFO phenomenon hype, but does this mean that
| a disk shaped "saucer" requires less energy than a craft with an
| elongated geometry? Wow
| Razengan wrote:
| On a side note, I like how The Expanse sidesteps the scientific
| issues of interstellar travel with alien magic.
|
| On yet another note, I read an unsettling sci-fi/theory about how
| the expansion of space is perhaps being caused by whatever tech
| allows interstellar travel in lightspeed-like time. So whatever
| intelligent species that evolved first may have a monopoly on
| such tech, while inadvertently altering the fabric of physics to
| make interstellar travel gradually impossible for any younger
| species.
| avaldeso wrote:
| > On a side note, I like how The Expanse sidesteps the
| scientific issues of interstellar travel with alien magic.
|
| I thought the "alien magic" behind the gates technology was the
| same old K. Thorne wormholes.
|
| > On yet another note, I read an unsettling sci-fi/theory about
| how the expansion of space is perhaps being caused by whatever
| tech allows interstellar travel in lightspeed-like time. So
| whatever intelligent species that evolved first may have a
| monopoly on such tech, while inadvertently altering the fabric
| of physics to make interstellar travel gradually impossible for
| any younger species.
|
| Do you have a link to read more about that? Reminds me of the
| FTL technology in the books "The Dark Forest" and "Death's End"
| by Liu Cixin.
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