7 ms·

Warp drive may actually be possible, NASA scientist says

52 points by kausikram 14y ago

Tossrock 14y ago
> "A trip to Alpha Centauri would take about two weeks. Traveling as fast as we are now currently able, it would take tens of thousands of years." This isn't true. Nuclear pulse drives built with currently available technology could achieve .05C [1], meaning a 4 light year trip would take ~80 years. [1]: http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...
- danielbarla 14y ago
  IIRC, that assumes we don't want to decelerate. Adding the fuel to decelerate also increases the fuel needed for the original acceleration itself, which then quickly becomes less feasible. In any case, I'm guessing they were referring to "current, tried and tested" technologies. Edit: I'm also having a slight chuckle at the estimated costs presented. Somehow, I'd think that just getting 40,000,000 t of spaceship into orbit would cost a bit more than 1 year of US GNP.
  - wcoenen 14y ago
    The mass added by the "fuel" of the orion nuclear pulse drive is negligible: a nuclear bomb has very little mass compared to the impulse boost you can extract from it. You could literally lift a city-sized space ship to orbit on the cheap with this technology. The problem is the nuclear fall-out for those left on the ground.
    - chii 14y ago
      if the launch system was all on another planet or moon, then this wouldn't be a problem. I can imagine you'd ride a rocket to the moon, and then the real spaceship is launched this way for inter planetary travel. It'd be like the old days of ocean liners, you stay on it for months on end, and a ship flies out may be once every year or so.
    - danielbarla 14y ago
      As a "fuel", yes, it is pretty efficient. That said, the "optimistic" version of the spaceship (representing the upper bounds of that specific technology), still came in at 400,000 tons, after a sort of miniaturisation. That's a lot of spaceship, and as far as I know, none of those calculations cater for launching from the planet's surface. If nothing else, that would require additional fuel, and it's not negligable, because each ton of extra fuel is pushing the 400,000 tons already loaded. It's a game of (greatly) diminishing returns.
    - jasonwatkinspdx 14y ago
      It's not that simple. You are vastly underestimating how much scaleup is required to sustain that acceleration up until you get a reasonable trip time. Here's the summary from NASA: "Here are four examples [large graphic][1] of what it would take to send a canister about the size of a Shuttle payload (or a school bus) past our nearest neighboring star...and allowing 900 years for it to make this journey. Well....If you use chemical engines like those that are on the Shuttle, well..., sorry, there isn’t enough mass in the universe to supply the rocket propellant you’d need. So let’s step up to next possibilities, nuclear rockets with a predicted performance that’s 10 to 20 times better! Well...it’s still not looking all that good. For a fission rocket you would need a BILLION SUPERTANKER size propellant tanks to get you there, and even with fusion rockets you would still need a THOUSAND SUPERTANKERS! Even if we look at the best conceivable performance that we could engineer based on today’s knowledge, say an Ion engine or an antimatter rocket whose performance was 100 times better that the shuttle engines, we would need about ten railway tanker sized propellant tanks. That doesn’t sound too bad, until you consider that we didn’t bring along any propellant to let us stop when we get to the other star system...or if we want to get there quicker than 9 centuries. Once you add the desire to actually stop at your destination, or if you want to get there sooner, you’re back at the incredible supertanker situation again, even for our best conceivable rockets. In conclusion, we’d really like to have a form of propulsion that doesn’t need any propellant! This implies the need to find some way to modify gravitational or inertial forces or to find some means to push against the very structure of spacetime itself." The rest of the website[2] has some good information, even if the organization is a bit disjoint. [1]: http://www.nasa.gov/centers/glenn/images/content/84509main_warp06.gif http://www.nasa.gov/centers/glenn/images/content/84509main_w... [2]: http://www.nasa.gov/centers/glenn/technology/warp/ipspaper.html http://www.nasa.gov/centers/glenn/technology/warp/ipspaper.h...
      - wcoenen 14y ago
        Your references are about rocket designs, which have limits to how fast they can expel reaction mass before they blow themselves up. Orion isn't really a rocket as it does the violent reaction outside of the spaceship. With Orion, the limit is how fast the pusher plate can be cooled or how much momentum can be handled by the shock absorbers. Granted, even with fusion bombs there is still a limit to how much energy and momentum you can extract from a certain mass, so the same concerns of diminishing returns apply. But according to Dyson's numbers, a 133 year trip to Alpha Centauri might be possible[1]. Even discounting interstellar travel, a trip time of only a few weeks to Mars with current technology sure sounds interesting to me. [1] http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)#Interstellar_missions http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...
  - InclinedPlane 14y ago
    To decelerate you'd use a magsail or an m2p2 type system. This is vastly more mass efficient than simply thrusting in the reverse direction.
ch0wn 14y ago
Previous discussion: http://news.ycombinator.com/item?id=4534359 http://news.ycombinator.com/item?id=4534359
WalterBright 14y ago
One issue about warp drives that I never see mentioned is one has to be careful one is not creating a perpetual motion device. Consider a warp drive that transports you from, say, earth's orbit to pluto's orbit. Now, you fall back towards earth's orbit. This means that the warp drive, in order to not violate conservation of energy, must require at least as much energy as the potential energy difference between the two positions.
- yk 14y ago
  Conservation of energy may or may not be valid in general relativity, at least in a naive understanding of conservation of energy. The technical explanation for this is, that conserved quantities are related to geometrical symmetries via Noethers theorem [1], and on a curved background these symmetries may or may not be there. ( A rather handwaving explanation would be, that there is no straightforward way to define the energy density of a gravitational field.) In fact it is possible to build a perpetuum mobile by just filling some region of space with dark energy. This region of space will then expand at constant energy density, therefore creating energy. [1] https://en.wikipedia.org/wiki/Noether%27s_theorem https://en.wikipedia.org/wiki/Noether%27s_theorem
  - maxerickson 14y ago
    "In fact it is possible" is a pretty strong way to talk about moving something that might not exist.
    - yk 14y ago
      Agreed, the wording is rather strong. But at least it is shorter than: "According to current understanding of GR and the contents of the universe it should be possible."
- egypturnash 14y ago
  I think you're describing a feature, not a bug. Especially if you can figure out a way to derive energy from the fall.
- 14y ago
shin_lao 14y ago
The article doesn't mention exotic matter. Did they find a way to build an engine without exotic matter?
- panacea 14y ago
  No. See: http://news.ycombinator.com/item?id=4534359 http://news.ycombinator.com/item?id=4534359
keyle 14y ago
Can someone explain what happens to time while you travel this way? Is your family at home going to be older when you come back from one of those trips?
- jonnathanson 14y ago
  Simple answer: probably not. You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. In fact, it's not moving very quickly at all. It's bending space around itself, while remaining within a flat and undistorted region of space inside the bubble. With respect to objects inside the bubble (its own frame of reference), the ship is not moving faster than light. (A beam of light inside the warp bubble will still travel faster than the ship, for instance). Basically, the ship is able to traverse distances faster than light can, but it isn't actually moving faster than light.
  - shanelja 14y ago
    Question 2: What would happen if you, whilst within this bubble, throw a coin attached to a piece of string out of the space ship, while still connected to the ship by the string and the coin exits the bubble? For instance, assuming the 'string' was made of a tough alloy, would it snap and the coin remain where it was at that time, would the ship be dragged back to where the coin is, or can the question not yet be answered by science? I ask because, presumably, if the coin can exit and be fine, this could be the basis for some kind of inter galaxy bus, no need to slow down the bus, merely drive your spaceship off the bus and exit the bubble when at your destination.
    - jonnathanson 14y ago
      Honestly? I'm not sure. I know there are at least a few physicists who post on HN, and perhaps one of them could provide a more informed estimation than I. Bear in mind, this article only addresses one of the many fundamental challenges to the Alcubierre drive: the energy requirements. Typically, the energy requirement has been considered the primary challenge to the feasibility of the device. But it's not the only one. Science hasn't completely worked out what would happen inside the bubble, or what happens to particles of matter interacting with the bubble at its leading edge. I've heard at least one speculation that the bubble would fill up with Hawking radiation and pretty much roast everyone alive inside it, like a big, interstellar dutch oven. Another issue is the stability of the bubble itself. Again, the article doesn't really address this issue. But it's a pretty big one.
keyle 14y ago
Can someone explain what happens to time while you travel this way? Is your family at home going to be older when you come back from one of those trips?
brudgers 14y ago
I am not a physicist - My understanding is that it is information that is limited to the speed of light. So the technology for sending people to a nearby star tends to be analogous to the to that between Clarke's hominids and the obelisk rather than that between Captain Kirk and Star Fleet. Warp drive will allow humans to pollenize, not colonize, other planets.
Tipzntrix 14y ago
If we can't move the spaceship fast enough, we'll move the space around it! No wonder all the sci-fi movies show the area around warp speed ships distorting. They must have been onto something. I don't want to know how a human could ever survive that though.
powertower 14y ago
I don't see how this will work considering the contraction of space-time right in front of the spaceship within this warp-bubble, will also in-turn cause a natural dilution of space-time right in front of the warp-bubble. Even if that was not true, how will the warp-drive propagate the warp-bubble field itself faster than C to grab onto space-time in a timely manner? It would seem to me this would cause the space-ship to feel that it's traveling faster than C, but to an outside observer it would only be traveling at C or less.

52 points by kausikram 14y ago

> "A trip to Alpha Centauri would take about two weeks. Traveling as fast as we are now currently able, it would take tens of thousands of years." This isn't true. Nuclear pulse drives built with currently available technology could achieve .05C [1], meaning a 4 light year trip would take ~80 years. [1]: http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...

danielbarla 14y ago
IIRC, that assumes we don't want to decelerate. Adding the fuel to decelerate also increases the fuel needed for the original acceleration itself, which then quickly becomes less feasible. In any case, I'm guessing they were referring to "current, tried and tested" technologies. Edit: I'm also having a slight chuckle at the estimated costs presented. Somehow, I'd think that just getting 40,000,000 t of spaceship into orbit would cost a bit more than 1 year of US GNP.
- wcoenen 14y ago
  The mass added by the "fuel" of the orion nuclear pulse drive is negligible: a nuclear bomb has very little mass compared to the impulse boost you can extract from it. You could literally lift a city-sized space ship to orbit on the cheap with this technology. The problem is the nuclear fall-out for those left on the ground.
  - chii 14y ago
    if the launch system was all on another planet or moon, then this wouldn't be a problem. I can imagine you'd ride a rocket to the moon, and then the real spaceship is launched this way for inter planetary travel. It'd be like the old days of ocean liners, you stay on it for months on end, and a ship flies out may be once every year or so.
  - danielbarla 14y ago
    As a "fuel", yes, it is pretty efficient. That said, the "optimistic" version of the spaceship (representing the upper bounds of that specific technology), still came in at 400,000 tons, after a sort of miniaturisation. That's a lot of spaceship, and as far as I know, none of those calculations cater for launching from the planet's surface. If nothing else, that would require additional fuel, and it's not negligable, because each ton of extra fuel is pushing the 400,000 tons already loaded. It's a game of (greatly) diminishing returns.
  - jasonwatkinspdx 14y ago
    It's not that simple. You are vastly underestimating how much scaleup is required to sustain that acceleration up until you get a reasonable trip time. Here's the summary from NASA: "Here are four examples [large graphic][1] of what it would take to send a canister about the size of a Shuttle payload (or a school bus) past our nearest neighboring star...and allowing 900 years for it to make this journey. Well....If you use chemical engines like those that are on the Shuttle, well..., sorry, there isn’t enough mass in the universe to supply the rocket propellant you’d need. So let’s step up to next possibilities, nuclear rockets with a predicted performance that’s 10 to 20 times better! Well...it’s still not looking all that good. For a fission rocket you would need a BILLION SUPERTANKER size propellant tanks to get you there, and even with fusion rockets you would still need a THOUSAND SUPERTANKERS! Even if we look at the best conceivable performance that we could engineer based on today’s knowledge, say an Ion engine or an antimatter rocket whose performance was 100 times better that the shuttle engines, we would need about ten railway tanker sized propellant tanks. That doesn’t sound too bad, until you consider that we didn’t bring along any propellant to let us stop when we get to the other star system...or if we want to get there quicker than 9 centuries. Once you add the desire to actually stop at your destination, or if you want to get there sooner, you’re back at the incredible supertanker situation again, even for our best conceivable rockets. In conclusion, we’d really like to have a form of propulsion that doesn’t need any propellant! This implies the need to find some way to modify gravitational or inertial forces or to find some means to push against the very structure of spacetime itself." The rest of the website[2] has some good information, even if the organization is a bit disjoint. [1]: http://www.nasa.gov/centers/glenn/images/content/84509main_warp06.gif http://www.nasa.gov/centers/glenn/images/content/84509main_w... [2]: http://www.nasa.gov/centers/glenn/technology/warp/ipspaper.html http://www.nasa.gov/centers/glenn/technology/warp/ipspaper.h...
    - wcoenen 14y ago
      Your references are about rocket designs, which have limits to how fast they can expel reaction mass before they blow themselves up. Orion isn't really a rocket as it does the violent reaction outside of the spaceship. With Orion, the limit is how fast the pusher plate can be cooled or how much momentum can be handled by the shock absorbers. Granted, even with fusion bombs there is still a limit to how much energy and momentum you can extract from a certain mass, so the same concerns of diminishing returns apply. But according to Dyson's numbers, a 133 year trip to Alpha Centauri might be possible[1]. Even discounting interstellar travel, a trip time of only a few weeks to Mars with current technology sure sounds interesting to me. [1] http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)#Interstellar_missions http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...
- InclinedPlane 14y ago
  To decelerate you'd use a magsail or an m2p2 type system. This is vastly more mass efficient than simply thrusting in the reverse direction.

ch0wn 14y ago

Previous discussion: http://news.ycombinator.com/item?id=4534359 http://news.ycombinator.com/item?id=4534359

WalterBright 14y ago

One issue about warp drives that I never see mentioned is one has to be careful one is not creating a perpetual motion device. Consider a warp drive that transports you from, say, earth's orbit to pluto's orbit. Now, you fall back towards earth's orbit. This means that the warp drive, in order to not violate conservation of energy, must require at least as much energy as the potential energy difference between the two positions.

yk 14y ago
Conservation of energy may or may not be valid in general relativity, at least in a naive understanding of conservation of energy. The technical explanation for this is, that conserved quantities are related to geometrical symmetries via Noethers theorem [1], and on a curved background these symmetries may or may not be there. ( A rather handwaving explanation would be, that there is no straightforward way to define the energy density of a gravitational field.) In fact it is possible to build a perpetuum mobile by just filling some region of space with dark energy. This region of space will then expand at constant energy density, therefore creating energy. [1] https://en.wikipedia.org/wiki/Noether%27s_theorem https://en.wikipedia.org/wiki/Noether%27s_theorem
- maxerickson 14y ago
  "In fact it is possible" is a pretty strong way to talk about moving something that might not exist.
  - yk 14y ago
    Agreed, the wording is rather strong. But at least it is shorter than: "According to current understanding of GR and the contents of the universe it should be possible."
egypturnash 14y ago
I think you're describing a feature, not a bug. Especially if you can figure out a way to derive energy from the fall.
14y ago

shin_lao 14y ago

The article doesn't mention exotic matter. Did they find a way to build an engine without exotic matter?

panacea 14y ago
No. See: http://news.ycombinator.com/item?id=4534359 http://news.ycombinator.com/item?id=4534359

keyle 14y ago

Can someone explain what happens to time while you travel this way? Is your family at home going to be older when you come back from one of those trips?

jonnathanson 14y ago
Simple answer: probably not. You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. In fact, it's not moving very quickly at all. It's bending space around itself, while remaining within a flat and undistorted region of space inside the bubble. With respect to objects inside the bubble (its own frame of reference), the ship is not moving faster than light. (A beam of light inside the warp bubble will still travel faster than the ship, for instance). Basically, the ship is able to traverse distances faster than light can, but it isn't actually moving faster than light.
- shanelja 14y ago
  Question 2: What would happen if you, whilst within this bubble, throw a coin attached to a piece of string out of the space ship, while still connected to the ship by the string and the coin exits the bubble? For instance, assuming the 'string' was made of a tough alloy, would it snap and the coin remain where it was at that time, would the ship be dragged back to where the coin is, or can the question not yet be answered by science? I ask because, presumably, if the coin can exit and be fine, this could be the basis for some kind of inter galaxy bus, no need to slow down the bus, merely drive your spaceship off the bus and exit the bubble when at your destination.
  - jonnathanson 14y ago
    Honestly? I'm not sure. I know there are at least a few physicists who post on HN, and perhaps one of them could provide a more informed estimation than I. Bear in mind, this article only addresses one of the many fundamental challenges to the Alcubierre drive: the energy requirements. Typically, the energy requirement has been considered the primary challenge to the feasibility of the device. But it's not the only one. Science hasn't completely worked out what would happen inside the bubble, or what happens to particles of matter interacting with the bubble at its leading edge. I've heard at least one speculation that the bubble would fill up with Hawking radiation and pretty much roast everyone alive inside it, like a big, interstellar dutch oven. Another issue is the stability of the bubble itself. Again, the article doesn't really address this issue. But it's a pretty big one.

keyle 14y ago

Can someone explain what happens to time while you travel this way? Is your family at home going to be older when you come back from one of those trips?

brudgers 14y ago

I am not a physicist - My understanding is that it is information that is limited to the speed of light. So the technology for sending people to a nearby star tends to be analogous to the to that between Clarke's hominids and the obelisk rather than that between Captain Kirk and Star Fleet. Warp drive will allow humans to pollenize, not colonize, other planets.

Tipzntrix 14y ago

If we can't move the spaceship fast enough, we'll move the space around it! No wonder all the sci-fi movies show the area around warp speed ships distorting. They must have been onto something. I don't want to know how a human could ever survive that though.

powertower 14y ago

I don't see how this will work considering the contraction of space-time right in front of the spaceship within this warp-bubble, will also in-turn cause a natural dilution of space-time right in front of the warp-bubble. Even if that was not true, how will the warp-drive propagate the warp-bubble field itself faster than C to grab onto space-time in a timely manner? It would seem to me this would cause the space-ship to feel that it's traveling faster than C, but to an outside observer it would only be traveling at C or less.