5 ms·

> Interstellar travel will consist of information travelling at the speed of light. Pretty much nothing else is practical. What's your reasoning for this? You

> Interstellar travel will consist of information travelling at the speed of light. Pretty much nothing else is practical. What's your reasoning for this? You would only have to accelerate at 1g for 3 years to hit 99.5% of the speed of light. You can use an electromagnetic shield for dust. It seems conceivable that this will be possible eventually, even if warp drives are not possible.

deleted 8y ago
[deleted]
analog31 8y ago
Indeed, and the benefit of traveling at 0.995 c is that a container of information doesn't suffer from degradation by the inverse square law as it travels over a large distance. It might actually cost less energy to transport information to far flung destinations that way, interstellar snail mail if you will. Some amount of information has to accompany the robot anyway, at the very least, its initial operating instructions. Of course whoever can get there at 0.996 c can take advantage of a market arbitrage. ;-)
- titanomachy 8y ago
  > a container of information doesn't suffer from degradation by the inverse square law Neither does a well-focused laser? EDIT: apparently it does, unless you manage to focus your laser very far away. Not sure how practical that is.
seppel 8y ago
1kg matter at 0.1c has a kinetic energy of 4.5x10^14 J It is certainly very expensive to spend this amount of energy. But is it also extremely challenging to even extract this out of an engine that has to accelerate itself. 1kg matter at 0.995c has a kinetic energy of 8x10^17 J This is the amount of enery you get if you convert 9kg in pure enery. That seems impossible to reach, even with an anti matter drive.
- selestify 8y ago
  A 9:1 ratio of fuel to mass doesn't sound particularly bad. Are there known theoretical limits to extracting the full E=mc^2 worth of energy from an object?
  - squirrelicus 8y ago
    No, you can do this with an antimatter rocket. Good luck capturing and containing antimatter and feeding/containing the explosion though. It's going to be practically impossible to get a 90% fuel ratio from an antimatter reactor, since literally 45% of your ship will be antimatter, by mass.
    - adrianN 8y ago
      You can also do this by feeding a black hole with ordinary matter and using Hawking radiation for propulsion. That is probably more practical than carrying around large quantities of antimatter. https://en.wikipedia.org/wiki/Black_hole_starship https://en.wikipedia.org/wiki/Black_hole_starship
      - m_mueller 8y ago
        If you watch PBS Spacetime on the 'Kugelblitz' idea, it seems that one way to go about it (over the course of a couple hundred years) would be to convert Mercury into a solar energy collecting swarm by use of Von Neumann probes and essentially harvest much of what the sun has to give. That kind of energy apparently would suffice to create tiny black holes (simply by redirecting enough energy to a focused point), which is I think the theoretically most efficient battery (or star system destroying bomb, depending on how you go about it...).
      - squirrelicus 8y ago
        I... can't.... Half of me recoils in horror at the impracticality, but the other half of me has a good enough armchair sense for the practicality of a high fuel ratio antimatter rocket, so I can't say you're wrong :P
squirrelicus 8y ago
Forgiving the problem of time dilation and the consequences it has on the expectations of conscious things... You can't just accelerate 1g for 3 years. What are you burning? A chemical rocket can easily achieve 1g. For about 5 minutes. A nuclear rocket is great, you can get 1g easy enough, but you're shoving hot hydrogen out the back end to get that thrust. The Rocket Equation teaches us that to get arbitrarily close to c, you need an exponential amount of your ship's mass to be propellant. I recommend this website to everyone in this thread that hasn't read it yet http://www.projectrho.com/public_html/rocket/ http://www.projectrho.com/public_html/rocket/ Edit: moreover, the problem of an EM deflector, or any kind of deflector, is that no matter what, no matter what, you must deal with the kinetic energy of the thing that just hit your deflector. It will (a) slow your ship down, and (b) cost you more energy, e.g. from your generator, to deflect it than it imparted on your vehicle. The energy numbers here are staggering. We have trouble theorizing how a relatively uncontrolled terawatt rocket might work, but imagine a terawatt reactor on your ship somehow powering a terawatt EMfield in front on your ship. And then you have to worry about dust that's not charged and thus goes right through EM fields.

deleted 8y ago

[deleted]

analog31 8y ago

Indeed, and the benefit of traveling at 0.995 c is that a container of information doesn't suffer from degradation by the inverse square law as it travels over a large distance. It might actually cost less energy to transport information to far flung destinations that way, interstellar snail mail if you will. Some amount of information has to accompany the robot anyway, at the very least, its initial operating instructions. Of course whoever can get there at 0.996 c can take advantage of a market arbitrage. ;-)

titanomachy 8y ago
> a container of information doesn't suffer from degradation by the inverse square law Neither does a well-focused laser? EDIT: apparently it does, unless you manage to focus your laser very far away. Not sure how practical that is.

seppel 8y ago

1kg matter at 0.1c has a kinetic energy of 4.5x10^14 J It is certainly very expensive to spend this amount of energy. But is it also extremely challenging to even extract this out of an engine that has to accelerate itself. 1kg matter at 0.995c has a kinetic energy of 8x10^17 J This is the amount of enery you get if you convert 9kg in pure enery. That seems impossible to reach, even with an anti matter drive.

selestify 8y ago
A 9:1 ratio of fuel to mass doesn't sound particularly bad. Are there known theoretical limits to extracting the full E=mc^2 worth of energy from an object?
- squirrelicus 8y ago
  No, you can do this with an antimatter rocket. Good luck capturing and containing antimatter and feeding/containing the explosion though. It's going to be practically impossible to get a 90% fuel ratio from an antimatter reactor, since literally 45% of your ship will be antimatter, by mass.
  - adrianN 8y ago
    You can also do this by feeding a black hole with ordinary matter and using Hawking radiation for propulsion. That is probably more practical than carrying around large quantities of antimatter. https://en.wikipedia.org/wiki/Black_hole_starship https://en.wikipedia.org/wiki/Black_hole_starship
    - m_mueller 8y ago
      If you watch PBS Spacetime on the 'Kugelblitz' idea, it seems that one way to go about it (over the course of a couple hundred years) would be to convert Mercury into a solar energy collecting swarm by use of Von Neumann probes and essentially harvest much of what the sun has to give. That kind of energy apparently would suffice to create tiny black holes (simply by redirecting enough energy to a focused point), which is I think the theoretically most efficient battery (or star system destroying bomb, depending on how you go about it...).
    - squirrelicus 8y ago
      I... can't.... Half of me recoils in horror at the impracticality, but the other half of me has a good enough armchair sense for the practicality of a high fuel ratio antimatter rocket, so I can't say you're wrong :P

squirrelicus 8y ago

Forgiving the problem of time dilation and the consequences it has on the expectations of conscious things... You can't just accelerate 1g for 3 years. What are you burning? A chemical rocket can easily achieve 1g. For about 5 minutes. A nuclear rocket is great, you can get 1g easy enough, but you're shoving hot hydrogen out the back end to get that thrust. The Rocket Equation teaches us that to get arbitrarily close to c, you need an exponential amount of your ship's mass to be propellant. I recommend this website to everyone in this thread that hasn't read it yet http://www.projectrho.com/public_html/rocket/ http://www.projectrho.com/public_html/rocket/ Edit: moreover, the problem of an EM deflector, or any kind of deflector, is that no matter what, no matter what, you must deal with the kinetic energy of the thing that just hit your deflector. It will (a) slow your ship down, and (b) cost you more energy, e.g. from your generator, to deflect it than it imparted on your vehicle. The energy numbers here are staggering. We have trouble theorizing how a relatively uncontrolled terawatt rocket might work, but imagine a terawatt reactor on your ship somehow powering a terawatt EMfield in front on your ship. And then you have to worry about dust that's not charged and thus goes right through EM fields.