3 ms·

You assume that warp drive actually moves you trough space, it doesn't. Problem solved. Here is a practical example: I decide to travel to Alpha Centauri, and

by w0000t 11y ago

You assume that warp drive actually moves you trough space, it doesn't. Problem solved. Here is a practical example: I decide to travel to Alpha Centauri, and I'm there. Time passed for everybody is the same. You cannot cause any problems. Note that you are not allowed to change reference frames, by doing this. This does sound illogical, since you move to some other location, but if you assume you didn't move, like we did, then it isn't. Actually the space moved, and that might cause some other problems we don't know about.

drdeca 11y ago
I think the alcubierre drive still violates causality if you go ftl. Iirc, the ftl violates causality thing isn't from going faster than light, but rather because where you end up is outside of the future light cone of where you started. It's also, I think, outside of your past light cone, so a single ftl trip in a straight line might not have retrocausality, but because the region outside of both the past and future light comes can be considered to be either before or after the start timeplace, by choosing a different reference frame, if you have two ftl trips, that is enough for causing past events. I think this doesn't matter what happens during the trips, just the start and end timeplaces.
- w0000t 11y ago
  The light cone only matters if you actually move. The accepted idioms from relativity don't apply here. I think we are just not talking about the same "warp" drive. The version that doesn't violate causality works like this. You are not allowed to accelerate( using normal rockets ) to near c velocity and then warp to a stop to some distant location. This would cause problems. Instead you will end up there with all of your accumulated velocity before the warp. Then you have to come to a stop the same way you accelerated. In other words, warp will change your location but not your velocity in spacetime.
  - drdeca 11y ago
    I am aware that the ship does not accelerate in space. No, I don't think we are talking about different warp drives, but either way it doesn't matter, (unless the one you are talking about has weird additional restrictions on things like what directions you can go or you can only use it once and only in a straight line, or something like that). What I'm saying is the "how you get there" doesn't matter. If you pick a point in spacetime, the future light cone of that point does not depend on your reference frame, and neither does the past light cone. And, no, I'm fairly sure that the light cone is still a thing even if you do not accelerate. So, pick a point X in space time, and a point Y which in some inertial frame of reference is "after" that point, but not inside the future light cone of X, such that your ftl device allows point X to influence point Y. Then there is some other frame of reference where point X is still not inside point Y's past or future light cones, but now is "after" point Y. Then, the same ftl device would allow point Y to influence point X, or other points in X's past light cone. (to simplify, assume that the ftl device does not have a maximum "speed" This implies that it can impact any future point. I'm pretty sure that the same line of reasoning with the two points still applies when ftl device is limited to a "speed" of twice c, but I am not well versed in relativity, so I am treating the "speed" of the ftl device as unlimited. I am putting "speed" in quotes to indicate that it isn't a literal speed, so much as a ratio of (I think) distance in some reference frame compared to time in the reference frame, within which the ftl device can reach.) Note that I have not at any point in this talked about a path between X and Y, or anything like that. So, you can't get around this by noting that the ftl device never actually goes faster than c in the space it is in, because none of the things deal with the ftl device moving, just influencing things outside of its light cone.
    - w0000t 11y ago
      You are clinging to light cones because that is what you know about relativity, but you don't understand it intuitively. I didn't get any new information from you last comment, just what has already been said. Warp and light cones clearly don't work. Does that mean that warp couldn't work at least in theory, no. Learn more about relativity( it is really interesting ), otherwise you will always be stuck in your frame of mind.
      - 11y ago

by w0000t 11y ago

drdeca 11y ago

I think the alcubierre drive still violates causality if you go ftl. Iirc, the ftl violates causality thing isn't from going faster than light, but rather because where you end up is outside of the future light cone of where you started. It's also, I think, outside of your past light cone, so a single ftl trip in a straight line might not have retrocausality, but because the region outside of both the past and future light comes can be considered to be either before or after the start timeplace, by choosing a different reference frame, if you have two ftl trips, that is enough for causing past events. I think this doesn't matter what happens during the trips, just the start and end timeplaces.

w0000t 11y ago
The light cone only matters if you actually move. The accepted idioms from relativity don't apply here. I think we are just not talking about the same "warp" drive. The version that doesn't violate causality works like this. You are not allowed to accelerate( using normal rockets ) to near c velocity and then warp to a stop to some distant location. This would cause problems. Instead you will end up there with all of your accumulated velocity before the warp. Then you have to come to a stop the same way you accelerated. In other words, warp will change your location but not your velocity in spacetime.
- drdeca 11y ago
  I am aware that the ship does not accelerate in space. No, I don't think we are talking about different warp drives, but either way it doesn't matter, (unless the one you are talking about has weird additional restrictions on things like what directions you can go or you can only use it once and only in a straight line, or something like that). What I'm saying is the "how you get there" doesn't matter. If you pick a point in spacetime, the future light cone of that point does not depend on your reference frame, and neither does the past light cone. And, no, I'm fairly sure that the light cone is still a thing even if you do not accelerate. So, pick a point X in space time, and a point Y which in some inertial frame of reference is "after" that point, but not inside the future light cone of X, such that your ftl device allows point X to influence point Y. Then there is some other frame of reference where point X is still not inside point Y's past or future light cones, but now is "after" point Y. Then, the same ftl device would allow point Y to influence point X, or other points in X's past light cone. (to simplify, assume that the ftl device does not have a maximum "speed" This implies that it can impact any future point. I'm pretty sure that the same line of reasoning with the two points still applies when ftl device is limited to a "speed" of twice c, but I am not well versed in relativity, so I am treating the "speed" of the ftl device as unlimited. I am putting "speed" in quotes to indicate that it isn't a literal speed, so much as a ratio of (I think) distance in some reference frame compared to time in the reference frame, within which the ftl device can reach.) Note that I have not at any point in this talked about a path between X and Y, or anything like that. So, you can't get around this by noting that the ftl device never actually goes faster than c in the space it is in, because none of the things deal with the ftl device moving, just influencing things outside of its light cone.
  - w0000t 11y ago
    You are clinging to light cones because that is what you know about relativity, but you don't understand it intuitively. I didn't get any new information from you last comment, just what has already been said. Warp and light cones clearly don't work. Does that mean that warp couldn't work at least in theory, no. Learn more about relativity( it is really interesting ), otherwise you will always be stuck in your frame of mind.
    - 11y ago