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It would alter our understanding of physics, so it would be both scientific and technological. From what I understand it would move our understanding of everyth

by api 12y ago

It would alter our understanding of physics, so it would be both scientific and technological. From what I understand it would move our understanding of everything even further from classical Newtonian physics and deeper into the relativity/quantum dichotomy realm. This thing could only have a relativistic macroscopic explanation and a quantum mechanical microscopic one. Classically it's impossible. One immediate consequence of a massless drive is that interstellar flight becomes far more "thinkable." It's not like we could build a starship tomorrow, but if this worked and if you could build a power plant (fusion?) capable of running a big one long enough, you could practically accelerate to meaningful fractions of the speed of light. Hell... I wonder if fission would be sufficient if you no longer had to take propellant? All that propellant mass could be plutonium instead, and you "burn" it slowly and jettison the spent fuel to progressively reduce your mass and increase your acceleration. Side note: if this keeps getting confirmed, the Fermi paradox becomes even more paradoxical. "They should be here." The impracticality of interstellar flight disappears as an excuse. If this effect is possible, something is clearly wrong. Either life itself is edge-of-impossibility improbable and most of the cosmos is sterile, we are the most advanced/complex life in the galaxy, or they are here and they're not communicating with us, or something even weirder.

marcosdumay 12y ago
This engine does not change the energy needed for interstelar travel, only reaction mass, and reaction mass is often free with an energy generator, because all of them waste some mass. If this thing is confirmed, it will be a much more significative scientific breakthrough than a technological one. That said, there is no reason for interestelar travel not to be viable. It's just too expensive for us with our current tech.
- XorNot 12y ago
  Reaction mass is definitely not free. You can get a lot of energy by a number of means, but the need to haul an ever increasing quantity of reaction mass for every bit of delta-v you want is the limiting factor. If you did not have to haul any reaction mass, then delta-v is limited solely by energy. Which means you can take some solar panels and thrust indefinitely up to light speed, with a vessel weighing a couple of kilos as opposed to megatons.
  - readerrrr 12y ago
    That would not work for several reasons. The energy produced from the solar cells would be negligible compared to the force of photons hitting the panels. If you instead of an engine just used a very large thin sail with a proportionately small cargo then you could theoretically reach c, but only close to stars. If you instead removed the sail and used antimater as an energy source, that would also work. The problem with all ideas is the interstellar medium, particles, photons. Drag from interstellar medium would damage and slow down the ship, even at lower percentages of c. Close to c everything would behave as shot from a particle accelerator and even photons from background radiation would be blueshifted to high energy gamma rays.
    - XorNot 12y ago
      I wasn't commenting on using photon reaction - I was commenting on using this hypothetical reactionless drive (which would, presumably, produce more thrust then photon force - which the claimed device does from relatively small amounts of power). If you had a reactionless drive, then the solar sail force would be negligible compared to the drive.
      - deleted 12y ago
        [deleted]
      - readerrrr 12y ago
        Even if the thrust from reactionless drive would be higher, it cannot be higher than the pressure produced by the photons on the solar cell, which you use to power the drive. If the developers claim that it does, then you have basically infinite energy.
    - guard-of-terra 12y ago
      I wonder which speed should a spacecraft have so that cosmic microwave background will be as bright as Sun from earth. This may explain "where is everybody", btw. Why do you need a Dyson sphere when there's free sunlight.
  - marcosdumay 12y ago
- DennisP 12y ago
  No, look up the rocket equation. Let's say your rocket is a mass driver, throwing rocks out the back end with electromagnets. You need two things: one is an energy source to power the electromagnets, like some kind of nuclear reactor, and the other is a big pile of rocks. The big problem for a rocket is that it's not just carrying the payload and reactor fuel, it's also carrying that big pile of rocks. For a given exhaust velocity, the faster you want to go, the bigger that rock pile has to be, which is even harder to push, and the challenge just multiplies. If you're trying to get to another star it's practically impossible. A reactionless drive would still have the nuclear reactor, but it gets rid of the big pile of rocks. Now higher speed no longer means you need a bigger rock pile, it just means you run the nuclear reactor longer. You'll need more reactor fuel but with the mass driver you needed that plus the bigger rock pile. Now you just need more reactor fuel, and that's relatively minor. So yeah, it'd be a huge technological breakthrough, if it actually works.
seanflyon 12y ago
Once you get up to speed reaction mass might be effectively free with something like this: http://en.wikipedia.org/wiki/Bussard_ramjet http://en.wikipedia.org/wiki/Bussard_ramjet
- ridgeguy 12y ago
  One thing I've wondered about with respect to bustard ramjets: they work by collecting hydrogen from the quite rarified interstellar medium and fusing it for energy release. Collection of hydrogen for fusion means that collected hydrogen atoms need to be in close proximity with one another for fusion to occur. This in turn means that interstellar hydrogen, essentially at rest with respect to the ramjet-equipped spaceship ploughing through the medium, has to be accelerated pretty much from the rest frame to the velocity of the ship as part of the collection process. This acceleration of hydrogen to ship velocity requires energy. At what ship velocity would more energy be expended collecting hydrogen than it would yield in ship reference frame when fused? This would seem to be an upper limit for Bussard-type propulsion systems.
  - gliese1337 12y ago
    Assuming proton-proton fusion, the speed limit is about 12% c, relative to the interstellar medium (http://www.projectrho.com/public_html/rocket/slowerlight.php http://www.projectrho.com/public_html/rocket/slowerlight.php). That depends, however, on the assumption that the initial kinetic energy of the incoming hydrogen is completely wasted- that the ramjet does not have "regenerative braking", so to speak, that can recover some of the pre-existing kinetic energy. That's a pretty reasonable assumption from an engineering point of view, but physics theoretically allows us to do better.
  - TheLoneWolfling 12y ago
    It's the same with jet engines, for similar reasons. (Although in practice your maximum speed is largely dictated by "melting the engine is considered shortsighted".) The theoretical upper-bound exhaust velocity of a Bussard ramjet is something like ~0.12c, assuming you start with 4 hydrogen and end with 1 helium. As such, the theoretical upper-bound speed limit relative to the interstellar medium of a Bussard ramjet is also ~0.12c. In actuality, it will be quite a bit lower, as quite a lot of the energy is carried off in the form of energetic photons and neutrinos. Personally? A Bussard ramjet will never work, even assuming we get the scoop part figured out. The lower bound on how fast it has to go before it can start working and the upper bound on how fast it can go are too close. Not to mention the Lawson criterion for hydrogen burning (4xH -> He), or, alternatively, the problem of containment of the catalyst and the beta-decay steps of the CNO cycle.

by api 12y ago

marcosdumay 12y ago

This engine does not change the energy needed for interstelar travel, only reaction mass, and reaction mass is often free with an energy generator, because all of them waste some mass. If this thing is confirmed, it will be a much more significative scientific breakthrough than a technological one. That said, there is no reason for interestelar travel not to be viable. It's just too expensive for us with our current tech.

XorNot 12y ago
Reaction mass is definitely not free. You can get a lot of energy by a number of means, but the need to haul an ever increasing quantity of reaction mass for every bit of delta-v you want is the limiting factor. If you did not have to haul any reaction mass, then delta-v is limited solely by energy. Which means you can take some solar panels and thrust indefinitely up to light speed, with a vessel weighing a couple of kilos as opposed to megatons.
- readerrrr 12y ago
  That would not work for several reasons. The energy produced from the solar cells would be negligible compared to the force of photons hitting the panels. If you instead of an engine just used a very large thin sail with a proportionately small cargo then you could theoretically reach c, but only close to stars. If you instead removed the sail and used antimater as an energy source, that would also work. The problem with all ideas is the interstellar medium, particles, photons. Drag from interstellar medium would damage and slow down the ship, even at lower percentages of c. Close to c everything would behave as shot from a particle accelerator and even photons from background radiation would be blueshifted to high energy gamma rays.
  - XorNot 12y ago
    I wasn't commenting on using photon reaction - I was commenting on using this hypothetical reactionless drive (which would, presumably, produce more thrust then photon force - which the claimed device does from relatively small amounts of power). If you had a reactionless drive, then the solar sail force would be negligible compared to the drive.
    - deleted 12y ago
      [deleted]
    - readerrrr 12y ago
      Even if the thrust from reactionless drive would be higher, it cannot be higher than the pressure produced by the photons on the solar cell, which you use to power the drive. If the developers claim that it does, then you have basically infinite energy.
  - guard-of-terra 12y ago
    I wonder which speed should a spacecraft have so that cosmic microwave background will be as bright as Sun from earth. This may explain "where is everybody", btw. Why do you need a Dyson sphere when there's free sunlight.
- marcosdumay 12y ago
DennisP 12y ago
No, look up the rocket equation. Let's say your rocket is a mass driver, throwing rocks out the back end with electromagnets. You need two things: one is an energy source to power the electromagnets, like some kind of nuclear reactor, and the other is a big pile of rocks. The big problem for a rocket is that it's not just carrying the payload and reactor fuel, it's also carrying that big pile of rocks. For a given exhaust velocity, the faster you want to go, the bigger that rock pile has to be, which is even harder to push, and the challenge just multiplies. If you're trying to get to another star it's practically impossible. A reactionless drive would still have the nuclear reactor, but it gets rid of the big pile of rocks. Now higher speed no longer means you need a bigger rock pile, it just means you run the nuclear reactor longer. You'll need more reactor fuel but with the mass driver you needed that plus the bigger rock pile. Now you just need more reactor fuel, and that's relatively minor. So yeah, it'd be a huge technological breakthrough, if it actually works.

seanflyon 12y ago

Once you get up to speed reaction mass might be effectively free with something like this: http://en.wikipedia.org/wiki/Bussard_ramjet http://en.wikipedia.org/wiki/Bussard_ramjet

ridgeguy 12y ago
One thing I've wondered about with respect to bustard ramjets: they work by collecting hydrogen from the quite rarified interstellar medium and fusing it for energy release. Collection of hydrogen for fusion means that collected hydrogen atoms need to be in close proximity with one another for fusion to occur. This in turn means that interstellar hydrogen, essentially at rest with respect to the ramjet-equipped spaceship ploughing through the medium, has to be accelerated pretty much from the rest frame to the velocity of the ship as part of the collection process. This acceleration of hydrogen to ship velocity requires energy. At what ship velocity would more energy be expended collecting hydrogen than it would yield in ship reference frame when fused? This would seem to be an upper limit for Bussard-type propulsion systems.
- gliese1337 12y ago
  Assuming proton-proton fusion, the speed limit is about 12% c, relative to the interstellar medium (http://www.projectrho.com/public_html/rocket/slowerlight.php http://www.projectrho.com/public_html/rocket/slowerlight.php). That depends, however, on the assumption that the initial kinetic energy of the incoming hydrogen is completely wasted- that the ramjet does not have "regenerative braking", so to speak, that can recover some of the pre-existing kinetic energy. That's a pretty reasonable assumption from an engineering point of view, but physics theoretically allows us to do better.
- TheLoneWolfling 12y ago
  It's the same with jet engines, for similar reasons. (Although in practice your maximum speed is largely dictated by "melting the engine is considered shortsighted".) The theoretical upper-bound exhaust velocity of a Bussard ramjet is something like ~0.12c, assuming you start with 4 hydrogen and end with 1 helium. As such, the theoretical upper-bound speed limit relative to the interstellar medium of a Bussard ramjet is also ~0.12c. In actuality, it will be quite a bit lower, as quite a lot of the energy is carried off in the form of energetic photons and neutrinos. Personally? A Bussard ramjet will never work, even assuming we get the scoop part figured out. The lower bound on how fast it has to go before it can start working and the upper bound on how fast it can go are too close. Not to mention the Lawson criterion for hydrogen burning (4xH -> He), or, alternatively, the problem of containment of the catalyst and the beta-decay steps of the CNO cycle.