Everyone always talks about FTL travel for spacecraft, but there's also an interesting perspective from weapons side (and this a reason to be a bit careful and think about some ethics as we move along). A FTL kinetic weapon would be devastating. If it comes with a collapsing warp bubble then there's basically a gamma ray "gun" that travels right in front of your mass that is traveling at tremendous speeds. You look a…
If you can twist the mass of jupiter into a bubble and accelerate it to lightspeed, you probably already have the means to destroy an earth-like planet. This is like a medieval person cautioning against the development of jet engines due to how fast they could make a catapult swing.
> the mass of jupiter ... means to destroy an earth-like planet.
What? That's a bit overkill, don't you think? I got a this pebble that'll do the job just fine.
General relativity actually tells us nothing about whether causality is absolute. You can easily make up spacetime configurations that violate causality and still conform to general relativity. It's just that most people believe that causality should be protected, because... well it would be really weird if it wasn't. But it's just a conjecture and not like a theorem or anything.
So we're traveling away from one another at 0.9c. I send a paper airplane in your direction at 500x the speed of light. You receive it and send it back (at 500c). Does it not arrive before I sent it, from my perspective?
Even at 500x the speed of light it took some time for me to receive it, and then you receive it some time after, so no it does not arrive before you send it. You'll just have to wait ~500x that time to see the corresponding visual. For me it's not weirder than sending and getting back the paper airplane at 500x the speed of sound and waiting for the sound. But I surely miss something.
Try this: https://www.youtube.com/watch?v=au0QJYISe4c c isn't defined as the speed of light - light travels at c, but so does everything else, when you factor in movement through time.
Good video! Thanks. c is still defined as "the speed of light" by NIST, even if it's not measured, and even if it's more universal than light. But I get your point (via the video) - photons are particles that move only in space, and not at all in time. Kind of makes your mind bend when you consider the cosmic background radiation hasn't aged a day since the beginning of the universe...and since it comes from everywhere equally, we really are the center of the universe. And so is everwhere else! Fun.
Funnily enough, the writers of ST:TNG had this idea too. The main computer of the Enterprise-D was huge (9 decks tall) and generated a subspace field so that optical processing ran faster than light.
Star Trek's tech vision is astounding. How many things in it have actually been built? I count: • Tablets (the padds) • VR "holodecks" • Computers that you can talk to and ask questions • "Tricorders" (smartphones?) • Turbolifts ( https://www.dezeen.com/2017/07/12/thyssenkrupp-unveils-world... ) Maybe we'll get to add a warp drive to the list by the time I die. What else?
If you ever try to follow what a holodeck can and can't do, you easily see that few of our technology predictions can even hold a candle to it. There's some finger-waggling in-universe to explain away the discrepancy, but the ‘fact’ is that a holodeck would create matter with which you can interact, out of thin air, and expand this volume of matter seemingly for kilometers around, while purportedly being located in a room. VR is but a feeble emulation of holodeck's glory.
"Warp drives in Einstein's general theory of relativity provide a unique mechanism for manned interstellar travel. It is well-known that the classical superluminal soliton[0] spacetimes require negative energy densities[1], likely sourced by quantum processes of the uncertainty principle. It has even been claimed by few that negative energy densities are a requirement of superluminal motion. However, recent studies s…
As a non physicist, the first question sounded like yes there is an ability to adjust speed if you can adjust the energy density distribution. I didn’t see an answer on the second beyond that the energy density required at the center is zero which leaves hope for a place to put a vehicle there at least, your question of flat space aside. Curious if I read this right tho.
From p. 12:
This could serve as a method of generating acceleration without modifying the total energy on the hypersurface. One could start with a finite energy distribution highly concentrated and uniformly distributed in a spherical shell around a spacecraft. The energy density is then increased
behind the spacecraft and decreased in front, without destroying or creating any additional energy. This increases the shift vector magnitude in the region where the spacecraft is located, transporting it to non-zero speeds relative to faraway observers. If the energy density is sufficiently concentrated behind the central observer, the relative speed becomes superluminal. This then operates as a tuneable solitonic configuration capable of superluminal speeds.
Would be interesting if paired with the harvesting of energy from a black hole. It is theorized that you can do this 'remotely' by slingshotting a laser around a black hole. This functions the same way a normal gravity assist does, except in this case it's photons, and not spacecraft. Shoot a laser around one side of a black hole, it returns to you around the other side, but at a higher energy wavelength. In this way…
If your laser beam doesn't spread so far that you can't harvest enough energy to be net positive, then the black hole is not going to be a safe distance away.
I supposed the term 'safe' is pretty relative in this case.
Funnily enough, the writers of ST:TNG had this idea too. The main computer of the Enterprise-D was huge (9 decks tall) and generated a subspace field so that optical processing ran faster than light.
Star Trek's tech vision is astounding. How many things in it have actually been built? I count: • Tablets (the padds) • VR "holodecks" • Computers that you can talk to and ask questions • "Tricorders" (smartphones?) • Turbolifts ( https://www.dezeen.com/2017/07/12/thyssenkrupp-unveils-world... ) Maybe we'll get to add a warp drive to the list by the time I die. What else?
Interestingly, most of those ideas were far earlier than ST:TNG was. Roddenberry had written a lot of them down based on 1960s science fiction during the time he was working on the original series.
He wanted to do the holodeck already back then, but there was no way to do it reasonably convincingly given the technology of the time.
Previous work seemed to conclude pretty strongly that superluminal warp travel required negative energy. What's the insight here that gets around that?
As far as I can tell, there is no such insight here - in the middle of page 13 they admit that in their solution, the weak energy condition is violated, and even that:
"No amount of modification to the configuration could get rid of these WEC-violating regions."
If I'm reading this correctly, all they have done is found a solution that has positive Eulerian energy density according to one particular reference frame, but not according to other reference frames. (I'm not a physicist, so please correct me if I'm wrong.)
The goal of warp drive is to produce a modified region of spacetime that makes it feasible to travel faster than light. There are an infinitude of different approaches. The authors in this paper find that if you impose specific constraints on the way the modified region of spacetime is shaped and evolves over time, you don't need the negative energy anymore. However, you do need a very high energy density, strong eno…
The sociology of this is fascinating. For my whole life I've heard that travelling faster than light is not only impossible, but so obviously absurdly impossible that only loons and sci-fi writers bother to think about it at all. Now I'm reading that "There are an infinitude of different approaches" to the problem! What exactly is the breakthrough that has led to this recent spurt of warp drive papers? As far as I ca…
Bear in mind that the "infinitude of different approaches" means an infinitude of purely mathematical solutions, all of which seem to involve physically impossible concepts like negative energy.
Star Trek's tech vision is astounding. How many things in it have actually been built? I count: • Tablets (the padds) • VR "holodecks" • Computers that you can talk to and ask questions • "Tricorders" (smartphones?) • Turbolifts ( https://www.dezeen.com/2017/07/12/thyssenkrupp-unveils-world... ) Maybe we'll get to add a warp drive to the list by the time I die. What else?
If you ever try to follow what a holodeck can and can't do, you easily see that few of our technology predictions can even hold a candle to it. There's some finger-waggling in-universe to explain away the discrepancy, but the ‘fact’ is that a holodeck would create matter with which you can interact, out of thin air, and expand this volume of matter seemingly for kilometers around, while purportedly being located in a…
In fact, if you consider the in-universe explanation of ‘holodeck creates fake matter that can't actually exist and function outside of the holodeck’, then things may possibly be even more impressive. So, presumably people discovered some kind of a different matter, with which we could interact, but which exists only temporarily on the holodeck thing. Since it flips in and out of existence when the holodeck activates or deactivates, it sounds like some kind of energy that masquerades and works as matter. But how much regular energy would you need to expend to hold this matter-energy in place and make it work? All discussion of teleportation and ‘transporter’ devices comes to conclusions that disassembling and assembling human-scale objects would require huge amounts of energy, like on levels of Kardashev Type II. But a holodeck pretty much does about the same kind of thing continuously, all the time while it's in use. Imagine, at the vague minimum, running a present-day country's worth of energy supply to power your VR box.