31 ms·

Warp Drive News

191 points by mellosouls 6y ago

whimsicalism 6y ago
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.
- tasty_freeze 6y ago
  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 6y ago
    > 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 6y ago
      You won't be downvoted if you've said this in the first place.
      - WarOnPrivacy 6y ago
        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 6y ago
      > 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?
      - whimsicalism 6y ago
        > 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 6y ago
        > 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 6y ago
      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.
      - whatshisface 6y ago
        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 6y ago
        [deleted]
        blincoln 6y ago
        > Hossenfelder doesn't claim that all the experts are wrong. "In his book, Hawking painted a neat picture for black hole evaporation that is now widely used. [...]. It’s simple, it’s intuitive, and it’s wrong."[1] When I read that quote, I originally took it at face value, because she seems like an expert in her field, and it certainly sounds plausible. But now, in the next writeup of hers that I've come across, I find a claim that the description of FTL and causality portrayed by every legit source I've ever encountered is wrong, and that FTL without violating causality is somehow possible within Einstein's framework. That's two incredible claims in as many writeups. Why haven't I seen similar claims from e.g. Brian Greene or David Deutsch? Is it something specific to her own theories? Is it from some branch of theoretical physics that's not accepted by mainstream physicists? Am I misunderstanding the claims? Etc. [1] http://backreaction.blogspot.com/2015/12/hawking-radiation-is-not-produced-at.html?m=1 http://backreaction.blogspot.com/2015/12/hawking-radiation-i...
    - tasty_freeze 6y ago
      > > 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.
    - qndreoi 6y ago
      Others here refer to the author as Dr. Hossenfelder. But to you she is Sabine. Would you refer to Brian Greene as Brian or Sean Carroll as Sean? It seems you are not even aware of your biases.
      - whimsicalism 6y ago
        > Others here refer to the author as Dr. Hossenfelder. But to you she is Sabine. Would you refer to Brian Greene as Brian or Sean Carroll as Sean? It seems you are not even aware of your biases. I doubt anyone is aware of all of their biases. I'm assuming you're making reference to gender bias - totally possible that I am susceptible to that, although I think: a. Sabine is a more unique name than Brian. b. In almost all discussions I see of her, she is referred to as Sabine - I was just following along with that precedence. She also goes by "Bee" and dislikes her last name [0] [1] [0]: https://blogs.scientificamerican.com/cross-check/physicist-sabine-hossenfelder-fears-theorists-lacking-data-may-succumb-to-wishful-thinking/ https://blogs.scientificamerican.com/cross-check/physicist-s... http://backreaction.blogspot.com/2007/09/name-game.html http://backreaction.blogspot.com/2007/09/name-game.html
- segfaultbuserr 6y ago
  https://news.ycombinator.com/newsguidelines.html 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.
- WarOnPrivacy 6y ago
  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.
LockAndLol 6y ago
> 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 6y ago
  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.
Animats 6y ago
"Note: This paper has not appeared yet. I will post a link here once I have a reference."
WJW 6y ago
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.
- dnautics 6y ago
  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 6y ago
    A flying saucer is quite flat though.
    - dnautics 6y ago
      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 6y ago
        secondary propulsion system for maneuvering out of warp- and how goofy would it be to walk around in a vertically standing ship in gravity?
deleted 6y ago
[deleted]
scarygliders 6y ago
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))
- purple-again 6y ago
  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 6y ago
    > “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.
JoeOfTexas 6y ago
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.
- simcop2387 6y ago
  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 6y ago
    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 6y ago
      > 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.
deleted 6y ago
[deleted]
hdhdurhdhdud 6y ago
“ 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
sitkack 6y ago
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 6y ago
  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.
  - chrismorgan 6y ago
    In that spirit, pointing lasers in front of a hypersonic aircraft to shift the shockwave in front of the vehicle rather than on it: https://www.thedrive.com/the-war-zone/33859/blasting-the-air-in-front-of-hypersonic-vehicles-with-lasers-could-unlock-unprecedented-speeds https://www.thedrive.com/the-war-zone/33859/blasting-the-air....
    - sitkack 6y ago
      Interesting, like a laser version of https://en.wikipedia.org/wiki/Drag-reducing_aerospike https://en.wikipedia.org/wiki/Drag-reducing_aerospike without the LSD Wave.
blamestross 6y ago
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.
- progman32 6y ago
  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 6y ago
    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.
    - edgyquant 6y ago
      Right if which is almost certainly not possible for a human to do
    - Dylan16807 6y ago
      Depends on your acceleration and whether "traverse" means you get to skip around a bunch of destinations or only make a single direct trip. If your acceleration is somewhere between .5G and 2G then every single hop costs a significant chunk of your lifetime, even if those hops can reach extremely far.
- qayxc 6y ago
  > 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.
Stierlitz 6y ago
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 :]
- krapp 6y ago
  Why it's almost as if Star Trek is fiction and the "canon" of a franchise spanning over fifty years of television, film and books has always been fluid and arbitrary.
  - Stierlitz 6y ago
    @krapp said: > Why it's almost as if Star Trek is fiction and the "canon" of a franchise spanning over fifty years of television, film and books has always been fluid and arbitrary. Despite it being fiction, you cannot arbitrarily mess with the basic mythology and still keep what makes the thing magical.
- edgyquant 6y ago
  And it’s never used again
Razengan 6y ago
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 6y ago
  > 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.
  - TeMPOraL 6y ago
    Since you mention The Dark Forest trilogy, it had some other dire implications along this lines. Spoiler: Bar glcr bs nqinaprq beqanapr orvat hfrq va vagrefgryyne jnef jnf n qvzrafvbanyvgl erqhpgvba jrncba. Bapr npgvingrq, vg cebprrqrq gb erzbir bar qvzrafvba sebz gur fheebhaqvat fcnpr. Gur rssrpg rkcnaqrq ng gur fcrrq bs yvtug naq arire fgbccrq, fb vg hygvzngryl - va ovyyvbaf bs lrnef - jbhyq qrfgebl gur ragver bofreinoyr havirefr. Gur obbx erirnyf gung gur irel ernfba bhe havirefr vf n guerr-qvzrafvbany bar, vafgrnq bs sbhe be gjryir be jungabg, vf orpnhfr bs guvf jrncba qrcyblrq va cnfg vagrefgryyne jnef.
  - Razengan 6y ago
    I think it was indeed from those books.
mrfusion 6y ago
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 6y ago
  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 6y ago
    Isn’t this artical saying you don’t need negative energy?
    - jleahy 6y ago
      No, faster than light needs negative energies.
- sgt101 6y ago
  Causality violation is an observation of physics.. not a law !
  - scarygliders 6y ago
    The way I think of it is this; If it's NOW in the Sol system, it's NOW in Alpha Centauri as well. (I guess it's difficult to think in these terms because we always only see a 4.367 years old "NOW" from Alpha Centauri.) There would be no violation of Causality if you had a ship which could instantly Jump between Sol and Alpha Centauri - you'd simply arrive there at NOW+<however long this Jump took> - whether it's seconds or picoseconds. If you sent a radio signal "Hi there!" from Sol to Alpha Centauri before this Jump, you'd be waiting for 4.367 years for it to arrive - which still isn't a violation of Causality, because it'd be NOW+4.367 years in Alpha Centauri and the same would be true in the Sol system. If your faster-than-light (faster-than-Causality) Drive wasn't an instantaneous Jump like above, Causality is still not violated, because you'd still be arriving at NOW + <however long it took> to travel between Sol & Alpha Centauri. Maybe you could only travel at twice the speed of light (twice the speed of Causality), in which case you'd arrive there in NOW + 2.1835 years
cfv 6y ago
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 6y ago
  https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field_interferometer https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field...
  - cfv 6y ago
    So... no?
    - generalizations 6y ago
      My reading is, 'needs better measuring tools'.
- JumpCrisscross 6y ago
  > bend the brane our reality resides on by any measurable amount, and also demonstrate this causes an actual translation in 3d space? Bends in spacetime creating measurable effects is how LIGO’s interferometers see gravity waves. You’re asking for a light bulb when we’ve barely begun grinding lenses for a telescope.
  - cfv 6y ago
    Apologies in advance if this sounds excessively rude, but I'm not asking for anything as there's noone to actually ask to, I'm asking about that. That distinction matters, since I personally find it easier to derive enthusiasm from concrete, tangible tools that may prevent the entire species as a thing from dying choked in a toxic miasma of our own creation than from the purely numeric advances in our grasp of the rules of a universe we're basically guests in.
ck2 6y ago
Apparently we've now moved onto "personal transporters" (a lazy writing device that was a step too far IMHO)

191 points by mellosouls 6y ago

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.

tasty_freeze 6y ago
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 6y ago
  > 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 6y ago
    You won't be downvoted if you've said this in the first place.
    - WarOnPrivacy 6y ago
      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 6y ago
    > 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?
    - whimsicalism 6y ago
      > 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 6y ago
        > 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 6y ago
    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.
    - whatshisface 6y ago
      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 6y ago
        [deleted]
      - blincoln 6y ago
        > Hossenfelder doesn't claim that all the experts are wrong. "In his book, Hawking painted a neat picture for black hole evaporation that is now widely used. [...]. It’s simple, it’s intuitive, and it’s wrong."[1] When I read that quote, I originally took it at face value, because she seems like an expert in her field, and it certainly sounds plausible. But now, in the next writeup of hers that I've come across, I find a claim that the description of FTL and causality portrayed by every legit source I've ever encountered is wrong, and that FTL without violating causality is somehow possible within Einstein's framework. That's two incredible claims in as many writeups. Why haven't I seen similar claims from e.g. Brian Greene or David Deutsch? Is it something specific to her own theories? Is it from some branch of theoretical physics that's not accepted by mainstream physicists? Am I misunderstanding the claims? Etc. [1] http://backreaction.blogspot.com/2015/12/hawking-radiation-is-not-produced-at.html?m=1 http://backreaction.blogspot.com/2015/12/hawking-radiation-i...
  - tasty_freeze 6y ago
    > > 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.
  - qndreoi 6y ago
    Others here refer to the author as Dr. Hossenfelder. But to you she is Sabine. Would you refer to Brian Greene as Brian or Sean Carroll as Sean? It seems you are not even aware of your biases.
    - whimsicalism 6y ago
      > Others here refer to the author as Dr. Hossenfelder. But to you she is Sabine. Would you refer to Brian Greene as Brian or Sean Carroll as Sean? It seems you are not even aware of your biases. I doubt anyone is aware of all of their biases. I'm assuming you're making reference to gender bias - totally possible that I am susceptible to that, although I think: a. Sabine is a more unique name than Brian. b. In almost all discussions I see of her, she is referred to as Sabine - I was just following along with that precedence. She also goes by "Bee" and dislikes her last name [0] [1] [0]: https://blogs.scientificamerican.com/cross-check/physicist-sabine-hossenfelder-fears-theorists-lacking-data-may-succumb-to-wishful-thinking/ https://blogs.scientificamerican.com/cross-check/physicist-s... http://backreaction.blogspot.com/2007/09/name-game.html http://backreaction.blogspot.com/2007/09/name-game.html
segfaultbuserr 6y ago
https://news.ycombinator.com/newsguidelines.html 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.
WarOnPrivacy 6y ago
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.

LockAndLol 6y ago

> 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 6y ago
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.

Animats 6y ago

"Note: This paper has not appeared yet. I will post a link here once I have a reference."

WJW 6y ago

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.

dnautics 6y ago
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 6y ago
  A flying saucer is quite flat though.
  - dnautics 6y ago
    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 6y ago
      secondary propulsion system for maneuvering out of warp- and how goofy would it be to walk around in a vertically standing ship in gravity?

deleted 6y ago

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scarygliders 6y ago

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))

purple-again 6y ago
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 6y ago
  > “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.

JoeOfTexas 6y ago

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.

simcop2387 6y ago
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 6y ago
  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 6y ago
    > 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.

deleted 6y ago

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hdhdurhdhdud 6y ago

“ 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

sitkack 6y ago

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 6y ago
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.
- chrismorgan 6y ago
  In that spirit, pointing lasers in front of a hypersonic aircraft to shift the shockwave in front of the vehicle rather than on it: https://www.thedrive.com/the-war-zone/33859/blasting-the-air-in-front-of-hypersonic-vehicles-with-lasers-could-unlock-unprecedented-speeds https://www.thedrive.com/the-war-zone/33859/blasting-the-air....
  - sitkack 6y ago
    Interesting, like a laser version of https://en.wikipedia.org/wiki/Drag-reducing_aerospike https://en.wikipedia.org/wiki/Drag-reducing_aerospike without the LSD Wave.

blamestross 6y ago

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.

progman32 6y ago
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 6y ago
  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.
  - edgyquant 6y ago
    Right if which is almost certainly not possible for a human to do
  - Dylan16807 6y ago
    Depends on your acceleration and whether "traverse" means you get to skip around a bunch of destinations or only make a single direct trip. If your acceleration is somewhere between .5G and 2G then every single hop costs a significant chunk of your lifetime, even if those hops can reach extremely far.
qayxc 6y ago
> 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.

Stierlitz 6y ago

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 :]

krapp 6y ago
Why it's almost as if Star Trek is fiction and the "canon" of a franchise spanning over fifty years of television, film and books has always been fluid and arbitrary.
- Stierlitz 6y ago
  @krapp said: > Why it's almost as if Star Trek is fiction and the "canon" of a franchise spanning over fifty years of television, film and books has always been fluid and arbitrary. Despite it being fiction, you cannot arbitrarily mess with the basic mythology and still keep what makes the thing magical.
edgyquant 6y ago
And it’s never used again

Razengan 6y ago

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 6y ago
> 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.
- TeMPOraL 6y ago
  Since you mention The Dark Forest trilogy, it had some other dire implications along this lines. Spoiler: Bar glcr bs nqinaprq beqanapr orvat hfrq va vagrefgryyne jnef jnf n qvzrafvbanyvgl erqhpgvba jrncba. Bapr npgvingrq, vg cebprrqrq gb erzbir bar qvzrafvba sebz gur fheebhaqvat fcnpr. Gur rssrpg rkcnaqrq ng gur fcrrq bs yvtug naq arire fgbccrq, fb vg hygvzngryl - va ovyyvbaf bs lrnef - jbhyq qrfgebl gur ragver bofreinoyr havirefr. Gur obbx erirnyf gung gur irel ernfba bhe havirefr vf n guerr-qvzrafvbany bar, vafgrnq bs sbhe be gjryir be jungabg, vf orpnhfr bs guvf jrncba qrcyblrq va cnfg vagrefgryyne jnef.
- Razengan 6y ago
  I think it was indeed from those books.

mrfusion 6y ago

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 6y ago
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 6y ago
  Isn’t this artical saying you don’t need negative energy?
  - jleahy 6y ago
    No, faster than light needs negative energies.
sgt101 6y ago
Causality violation is an observation of physics.. not a law !
- scarygliders 6y ago
  The way I think of it is this; If it's NOW in the Sol system, it's NOW in Alpha Centauri as well. (I guess it's difficult to think in these terms because we always only see a 4.367 years old "NOW" from Alpha Centauri.) There would be no violation of Causality if you had a ship which could instantly Jump between Sol and Alpha Centauri - you'd simply arrive there at NOW+<however long this Jump took> - whether it's seconds or picoseconds. If you sent a radio signal "Hi there!" from Sol to Alpha Centauri before this Jump, you'd be waiting for 4.367 years for it to arrive - which still isn't a violation of Causality, because it'd be NOW+4.367 years in Alpha Centauri and the same would be true in the Sol system. If your faster-than-light (faster-than-Causality) Drive wasn't an instantaneous Jump like above, Causality is still not violated, because you'd still be arriving at NOW + <however long it took> to travel between Sol & Alpha Centauri. Maybe you could only travel at twice the speed of light (twice the speed of Causality), in which case you'd arrive there in NOW + 2.1835 years

cfv 6y ago

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 6y ago
https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field_interferometer https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field...
- cfv 6y ago
  So... no?
  - generalizations 6y ago
    My reading is, 'needs better measuring tools'.
JumpCrisscross 6y ago
> bend the brane our reality resides on by any measurable amount, and also demonstrate this causes an actual translation in 3d space? Bends in spacetime creating measurable effects is how LIGO’s interferometers see gravity waves. You’re asking for a light bulb when we’ve barely begun grinding lenses for a telescope.
- cfv 6y ago
  Apologies in advance if this sounds excessively rude, but I'm not asking for anything as there's noone to actually ask to, I'm asking about that. That distinction matters, since I personally find it easier to derive enthusiasm from concrete, tangible tools that may prevent the entire species as a thing from dying choked in a toxic miasma of our own creation than from the purely numeric advances in our grasp of the rules of a universe we're basically guests in.

ck2 6y ago

Apparently we've now moved onto "personal transporters" (a lazy writing device that was a step too far IMHO)