That's what I mean by "seeing" -- observing, according to some reference frame, FTL travel. The point of the warp drive is that within its own reference frame it is not traveling faster than light. But relative to some reference frame it must be (even if they aren't literally watching it with a telescope). And going FTL according to any reference frame violates relativity.
So what if a radio signal goes slower than a spaceship? That doesn't mean anything.
If the speed of light had no relationship to spacetime, if this was a Newtonian universe, then yeah, what would it matter? But this is not the case, and the speed of light is intimately related to the nature of space and time and as a consequence the ordering of events and causality.
You can google "speed of light causality" to find that every source agrees. I like this page because it has graphs.
Strange how real physicists have no trouble with this stuff
Ha! And you think that's because they agree with you that there's no relationship between c and causality?
No, physicists have "no trouble" with this because they know when they're looking at things outside the bounds of known physics. The Alcubierre drive is a valid solution for the equations of General Relativity, but that doesn't mean you can actually create one in this universe. In particular, the Alcubierre drive requires that the warp in space already exists, and there is no way to enter or exit it. Also, there are the implications with causality if you did exit it (if you didn't then you never interact with the rest of the universe so it's no problem). And that "exotic matter" you tossed out isn't just some engineering problem. Negative mass is also something not known in current physics.
I'm not saying it's impossible. I'm saying it goes against the known laws of physics. Many people, especially physicists, hope that those laws are wrong and in such a way that FTL is possible.
That's the whole point -- they don't need to see you actually in transit. They only need to see two causally linked events -- you getting in your ship at point A, and getting out at point B -- with a space-like interval in between them from their reference frame.
So whether it's a warp ship, or a wizard instantaneously teleporting, it still causes problems.
Note that the method of FTL communication does not matter. The author uses an "ansible", what is essentially a magical instant communication device from Sci-fi. It can be assumed that the ansible itself violates no laws of physics.
All that matters is how the various sub-luminal reference frames see the ordering of events as a result.
I understand how this solution to GR allows one to avoid going FTL locally. I do not see how this gets around the larger perspective of how the sequence of events appears to other refererence frames. The whole point of Relativity is that the laws of physics must appear to hold according to everyone.
They would see you arrive at your destination faster than the speed of light but not before you left.
You're at Vega, 25 light years away. You send a radio message "I'm coming!" and hop in your warp drive and head to earth at 5x the speed of light. In 5 years I see you arrive at earth. 20 years later the message announcing your departure arrives.
So yes, I saw you arrive before I saw you leave.
As well there is no real reason to believe that my future self could not go back in time and have caused the universe to be in the state that it is currently in.
Causality is just an assumption, sure.
Also it looks like you don't have a firm understanding of special or general relativity.
But an assumption fundamental to both theories (and all of physics).
For example, objects that recede past our cosmic event horizon are moving away from us faster than the speed of light
Well yeah, and by virtue of doing so there is no possible way that we can ever interact with them, ergo no possible causality conflict.
The question is what would happen if they were coming at us. Oh sure maybe in their local space they aren't traveling faster than c, but if a ship leaves Vega and heads to earth at Warp 10, then I'll witness their arrival before I witness their departure.
At this point it's no different than if they somehow traveled FTL through unwarped space, or simply *poofed* here by magic. From my reference frame, the two events have a space-like separation, and causality has been violated.
Which is why the descriptions of Alcubierre drives I have read suggest that the ship itself would be separated causally from the rest of the universe, and that there's no known way to actually get the ship in or out of the bubble and that the bubble has to already exist.
What I find very interesting is the possible implication that such "effective FTL" is okay as long as there can't be any causality violations as a result.
In the real world, today, the phase velocity of light can easily exceed the speed of light in a vacuum.
That's because phase velocity is not a "thing", it's a logical description of frequency distribution. Just like "the dot made by a laser" is just a logical description of where a laser beam is interacting with an object. Sweeping the laser across the moon would have the location of the spot moving FTL, but it's not a "thing". The actual things are the photons from the laser moving from the laser to the moon.
There's no information transfer, either, due to the conditions of travel at that speed, but there's no time travel.
There's no time travel because there's no information transfer because phase velocity is not a thing.
A warp ship bringing people across the universe is a thing that conveys information, and so you have causality problems.
But that's the point of how warp drive works - you bend space so that you don't travel faster than light.
You locally don't. The warp ship doesn't actually accelerate at all. This is how you get around the relativistic energy equation.
However, someone will observe you traveling faster than light, going from point A to point B faster than light would travel the same distance. If nobody sees you traveling faster than light, then how can you say you did so at all?
And the whole point of relativity is that the laws of physics have to hold everywhere. That observer, depending on their own velocity in space-time, potentially see you arrive at your destination before you left, violating causality according to them.
Given a few such warp ships, you could even arrange it so that that person would receive a message they had written and sent with you before they had actually written it. And then causality is broken for everyone.
But hey, maybe it's not a causal universe! I await their experiments.
As far as I understand it warp drive doesnt break the speed of light locally, so I recon no weird time reversal stuff can happen.
In Relativity, traveling faster than light relative to any reference frame, via any method, presents problems with causality. And the whole point of a Warp Drive is that someone will agree that you went faster than light, and thus went backward in time.
When I last read about the Alcubierre drive, one relevant point that was mentioned was that the inside of the warp field is causally separated from the outside, which solves the problems of causality while in transit, but raises the question of how one starts or ends the journey.
The ridiculous amount of energy required was another problem, more of a practical "how would you do that?" issue rather than a "how is it even possibly in theory?" question.
But the thing is -- it may actually be possible to do this in our universe. And the assumptions of constant c and General Principle of Relativity may also be correct. Which may mean that the assumption of causality isn't. What a universe that would be.
Yeah it's almost like someone decided to put a funny pattern on some paper
Almost, but actually not.
If diamonds were the foundation of our currency then it would make sense to restrict the supply. Currencies must of necessity be scarce or they become worthless, and in the case of paper that scarcity must of necessity be artificial. That it is artificial and thus allows for overprinting and the resultant devaluation is why many (myself not among them) would much prefer a gold-backed currency. They choose gold as opposed to, say, diamonds, because gold represents actual scarcity and thus makes it extremely unlikely that any entity could flood the market and drop the bottom out of the price.
Controlling and limiting the supply of currency helps everyone participating in the economy.
Limiting the supply of diamonds only helps those participating in the scam.
Of course price is only a matter of consensus blah blah blah everything is the same so let's not distinguish...
Except what do you think would actually happen if DeBeer's got hit in the metaphorical head and unleashed the floodgates, or Russia started exploiting this diamond source to its maximum potential, or anything else happened to change the availability of diamonds to reflect their true scarcity?
Yeah, virtually nobody would agree to pay the prices currently being asked. The only reason anyone does is because of the artificial scarcity (which relatively few even know is artificial).
It's like these guys are sitting there covering their ears and shouting "LA LA LA LA I CAN'T HEAR YOU!".
If I had a few billion dollars for every time the "hardcore" proclaimed that Nintendo's latest gaming system would be (or is) a flop and it ends up (or is currently) dominating... I'd be Nintendo since the just before the launch of the DS.
What I find really funny is that they tend to want Nintendo to make a console that is on par with the most powerful of its generation, while not taking any risks on 'gimmicky' controls or features -- the Gamecube strategy.
Which still made Nintendo money, just not nearly as much, so you know.
You do realize that it's out-paced the original DS
Of course not, because while they "don't wish ill on the company", they would rather replace the reality of success with their personal fantasty of failure.
Very few people had a chance to play Pacman Vs. since they couldn't afford it.
Yeah, they couldn't afford a Gamecube.
As Penny Arcade said when people complained about FF: Crystal Chronicles -- it's much easier to find 3 other friends who have GBAs than to find one friend with a GC.
Metroid Prime: Corruption would have been awesome with the GC controls, but was simply amazing with the Wiimote. I loved it so much I got the Prime Trilogy collection just so I could replay the previous two with the Wiimote.
Unless you meant Other M. That was beyond dissappointing.
Venus is visible to the naked eye before the sun even fully sets. Kinda different than an asteroid.
But the main thing is I was implicitly tying "tracking" and "discovery" in my head, since most 'normal' uses of radar the two coincide. Discovering asteroids with radar would be ridiculous. Examining objects already known allows the use of high-gain antennae and so is much more feasible as the AC pointed out.
No amount of verbal or written instigation justifies murder.
Of course not, but that doesn't mean you can act as if cause and effect no longer apply and the results are not predictable.
Furthermore, no amount of verbal or written instigation should make you accountable for the actions of others.
Maybe in a court of law. But you should always hold yourself accountable for the completely expected consequences of your actions, even if certain steps in the chain of causality involve other sentient beings.
For example:
You walk into a bar and tell an ex-marine you know has a drinking problem and rage issues that dogs are fucking scum and you wish more of them were dying from IEDs.
Do your actions justify the savage beating you will receive? No, of course not.
Do your actions explain the savage beating? Are you responsible for doing something so stupid that you had to have known would result in that beating? Yeah. I mean if you smashed your face into a wall the resulting pain is obviously your fault. So just because this person has free will and might have gone against everything you knew about them and not hit you, you're free from blame? I don't think so.
But I also don't think blame is a zero-sum game, and a person is completely responsible for their own actions. That marine I made up should seriously get some counseling when they get out of jail.
Plastic surgery was originally developed to repair damage by accident, injury or disease.
And still is, called restorative plastic surgery, as opposed to cosmetic which is the more common and commonly known type today.
In high school, I saw a slideshow presentation by a restorative plastic surgeon. It was like 80 slides of 3rd degree burns, skin grafts, feet caught in paper shredders, and on and on. One of the first slides was a little girl who'd been hit in the face by a tire kicked off by an accident on the other side of the road. You could see her teeth through her cheek.
Several students threw up.
I have no idea what they were thinking. Other than convincing the "pre-med" students to find another major when they went to college. But why did the rest of us have to watch?
I don't remember ever stopping picking on Nike. But when the court ruled that they were allowed to lie in advertisements about ceasing to use sweatshops when they had not, it seems they were the winners of the PR war.
The ESA radar systems are for tracking space debris orbiting the Earth not for tracking asteroids.
Well unless the asteroids were captured by earth's gravity.:)
But yeah, detecting radio signals broadcast from earth then bounced off an asteroid would be redonculously hard. It's hard enough using the sun as our illumination.
The "even" refers to the impact, not the number, as "city killers" were used as the scary threat. They aren't scary.
So because the GGP or whoever that didn't even know what they were talking about said that, your risk analysis is limited to those types of events despite the probabilities you used not even lining up? Fine, whatever. Now think beyond that. Think about the actual problem.
In other words, probability is random. Thanks for the update.
No, in other words, instead of relying on the odds that the cards turned down are favorable to us, we should actually try to look at the cards and see what the reality is.
As it is, even finding 1% of the threats is better than nothing and not useless.
Not literally, but qualitatively yes it is. An insurance policy that covers 1% would be called useless, and correctly so, even if it doesn't literally do nothing. The difference is negligible. I don't want to treat problems in a negligible fashion.
But hey if you just meant "token" as a % of resources, then a fully-funded, vastly more effective effort would be such, like I was saying we could do that and address many other problems to. But we aren't even close to that. Because we aren't taking the problem at all seriously.
Wow, you live in a very binary world. Technology in astronomy has improved a lot over the past decades. I expect more improvements in the future.
That's rich after that last part. But so what. Our astronomy and technology is good enough now, so we should be doing it. A deadly asteroid is not going to wait until you think it's worth it.
It was an example of something that was more important, much more of an immediate threat that is being mostly ignored.
We have multiple satellites studying the sun continuously, many scientists studying the data to figure out solar weather patterns, and even solar weather predictions used to aid satellite operators and the ISS. But now we both agree that this effort is negligible and negligible is not good enough. What happened to the binary "not literally useless"?
The simple facts are that resources are limited, and should be prioritized accordingly.
Doi. And the simple facts are that if we decided to make these things priorities we could easily do both and many other things.
So, do you think we shouldn't, or do you agree that we should have an effective object discovery program?
Slashdot Mirror
That's what I mean by "seeing" -- observing, according to some reference frame, FTL travel. The point of the warp drive is that within its own reference frame it is not traveling faster than light. But relative to some reference frame it must be (even if they aren't literally watching it with a telescope). And going FTL according to any reference frame violates relativity.
So what if a radio signal goes slower than a spaceship? That doesn't mean anything.
If the speed of light had no relationship to spacetime, if this was a Newtonian universe, then yeah, what would it matter? But this is not the case, and the speed of light is intimately related to the nature of space and time and as a consequence the ordering of events and causality.
You can google "speed of light causality" to find that every source agrees. I like this page because it has graphs.
Strange how real physicists have no trouble with this stuff
Ha! And you think that's because they agree with you that there's no relationship between c and causality?
No, physicists have "no trouble" with this because they know when they're looking at things outside the bounds of known physics. The Alcubierre drive is a valid solution for the equations of General Relativity, but that doesn't mean you can actually create one in this universe. In particular, the Alcubierre drive requires that the warp in space already exists, and there is no way to enter or exit it. Also, there are the implications with causality if you did exit it (if you didn't then you never interact with the rest of the universe so it's no problem). And that "exotic matter" you tossed out isn't just some engineering problem. Negative mass is also something not known in current physics.
I'm not saying it's impossible. I'm saying it goes against the known laws of physics. Many people, especially physicists, hope that those laws are wrong and in such a way that FTL is possible.
That's the whole point -- they don't need to see you actually in transit. They only need to see two causally linked events -- you getting in your ship at point A, and getting out at point B -- with a space-like interval in between them from their reference frame.
So whether it's a warp ship, or a wizard instantaneously teleporting, it still causes problems.
Here's a good description.
Note that the method of FTL communication does not matter. The author uses an "ansible", what is essentially a magical instant communication device from Sci-fi. It can be assumed that the ansible itself violates no laws of physics.
All that matters is how the various sub-luminal reference frames see the ordering of events as a result.
I understand how this solution to GR allows one to avoid going FTL locally. I do not see how this gets around the larger perspective of how the sequence of events appears to other refererence frames. The whole point of Relativity is that the laws of physics must appear to hold according to everyone.
They would see you arrive at your destination faster than the speed of light but not before you left.
You're at Vega, 25 light years away. You send a radio message "I'm coming!" and hop in your warp drive and head to earth at 5x the speed of light. In 5 years I see you arrive at earth. 20 years later the message announcing your departure arrives.
So yes, I saw you arrive before I saw you leave.
As well there is no real reason to believe that my future self could not go back in time and have caused the universe to be in the state that it is currently in.
Causality is just an assumption, sure.
Also it looks like you don't have a firm understanding of special or general relativity.
But an assumption fundamental to both theories (and all of physics).
For example, objects that recede past our cosmic event horizon are moving away from us faster than the speed of light
Well yeah, and by virtue of doing so there is no possible way that we can ever interact with them, ergo no possible causality conflict.
The question is what would happen if they were coming at us. Oh sure maybe in their local space they aren't traveling faster than c, but if a ship leaves Vega and heads to earth at Warp 10, then I'll witness their arrival before I witness their departure.
At this point it's no different than if they somehow traveled FTL through unwarped space, or simply *poofed* here by magic. From my reference frame, the two events have a space-like separation, and causality has been violated.
Which is why the descriptions of Alcubierre drives I have read suggest that the ship itself would be separated causally from the rest of the universe, and that there's no known way to actually get the ship in or out of the bubble and that the bubble has to already exist.
What I find very interesting is the possible implication that such "effective FTL" is okay as long as there can't be any causality violations as a result.
In the real world, today, the phase velocity of light can easily exceed the speed of light in a vacuum.
That's because phase velocity is not a "thing", it's a logical description of frequency distribution. Just like "the dot made by a laser" is just a logical description of where a laser beam is interacting with an object. Sweeping the laser across the moon would have the location of the spot moving FTL, but it's not a "thing". The actual things are the photons from the laser moving from the laser to the moon.
There's no information transfer, either, due to the conditions of travel at that speed, but there's no time travel.
There's no time travel because there's no information transfer because phase velocity is not a thing.
A warp ship bringing people across the universe is a thing that conveys information, and so you have causality problems.
But that's the point of how warp drive works - you bend space so that you don't travel faster than light.
You locally don't. The warp ship doesn't actually accelerate at all. This is how you get around the relativistic energy equation.
However, someone will observe you traveling faster than light, going from point A to point B faster than light would travel the same distance. If nobody sees you traveling faster than light, then how can you say you did so at all?
And the whole point of relativity is that the laws of physics have to hold everywhere. That observer, depending on their own velocity in space-time, potentially see you arrive at your destination before you left, violating causality according to them.
Given a few such warp ships, you could even arrange it so that that person would receive a message they had written and sent with you before they had actually written it. And then causality is broken for everyone.
But hey, maybe it's not a causal universe! I await their experiments.
As far as I understand it warp drive doesnt break the speed of light locally, so I recon no weird time reversal stuff can happen.
In Relativity, traveling faster than light relative to any reference frame, via any method, presents problems with causality. And the whole point of a Warp Drive is that someone will agree that you went faster than light, and thus went backward in time.
When I last read about the Alcubierre drive, one relevant point that was mentioned was that the inside of the warp field is causally separated from the outside, which solves the problems of causality while in transit, but raises the question of how one starts or ends the journey.
The ridiculous amount of energy required was another problem, more of a practical "how would you do that?" issue rather than a "how is it even possibly in theory?" question.
But the thing is -- it may actually be possible to do this in our universe. And the assumptions of constant c and General Principle of Relativity may also be correct. Which may mean that the assumption of causality isn't. What a universe that would be.
Yeah it's almost like someone decided to put a funny pattern on some paper
Almost, but actually not.
If diamonds were the foundation of our currency then it would make sense to restrict the supply. Currencies must of necessity be scarce or they become worthless, and in the case of paper that scarcity must of necessity be artificial. That it is artificial and thus allows for overprinting and the resultant devaluation is why many (myself not among them) would much prefer a gold-backed currency. They choose gold as opposed to, say, diamonds, because gold represents actual scarcity and thus makes it extremely unlikely that any entity could flood the market and drop the bottom out of the price.
Controlling and limiting the supply of currency helps everyone participating in the economy.
Limiting the supply of diamonds only helps those participating in the scam.
Of course price is only a matter of consensus blah blah blah everything is the same so let's not distinguish...
Except what do you think would actually happen if DeBeer's got hit in the metaphorical head and unleashed the floodgates, or Russia started exploiting this diamond source to its maximum potential, or anything else happened to change the availability of diamonds to reflect their true scarcity?
Yeah, virtually nobody would agree to pay the prices currently being asked. The only reason anyone does is because of the artificial scarcity (which relatively few even know is artificial).
It's like these guys are sitting there covering their ears and shouting "LA LA LA LA I CAN'T HEAR YOU!".
If I had a few billion dollars for every time the "hardcore" proclaimed that Nintendo's latest gaming system would be (or is) a flop and it ends up (or is currently) dominating ... I'd be Nintendo since the just before the launch of the DS.
What I find really funny is that they tend to want Nintendo to make a console that is on par with the most powerful of its generation, while not taking any risks on 'gimmicky' controls or features -- the Gamecube strategy.
Which still made Nintendo money, just not nearly as much, so you know.
You do realize that it's out-paced the original DS
Of course not, because while they "don't wish ill on the company", they would rather replace the reality of success with their personal fantasty of failure.
If Curiosity encountered a prostate on Mars, I'm sure it'd want to investigate it with its laser, and possibly drill.
Very few people had a chance to play Pacman Vs. since they couldn't afford it.
Yeah, they couldn't afford a Gamecube.
As Penny Arcade said when people complained about FF: Crystal Chronicles -- it's much easier to find 3 other friends who have GBAs than to find one friend with a GC.
Metroid Prime: Corruption would have been awesome with the GC controls, but was simply amazing with the Wiimote. I loved it so much I got the Prime Trilogy collection just so I could replay the previous two with the Wiimote.
Unless you meant Other M. That was beyond dissappointing.
You can't go by just clock speed.
Jeebus, yes. That quote was like a flashback to the early 00's.
Venus is visible to the naked eye before the sun even fully sets. Kinda different than an asteroid.
But the main thing is I was implicitly tying "tracking" and "discovery" in my head, since most 'normal' uses of radar the two coincide. Discovering asteroids with radar would be ridiculous. Examining objects already known allows the use of high-gain antennae and so is much more feasible as the AC pointed out.
No amount of verbal or written instigation justifies murder.
Of course not, but that doesn't mean you can act as if cause and effect no longer apply and the results are not predictable.
Furthermore, no amount of verbal or written instigation should make you accountable for the actions of others.
Maybe in a court of law. But you should always hold yourself accountable for the completely expected consequences of your actions, even if certain steps in the chain of causality involve other sentient beings.
For example:
You walk into a bar and tell an ex-marine you know has a drinking problem and rage issues that dogs are fucking scum and you wish more of them were dying from IEDs.
Do your actions justify the savage beating you will receive? No, of course not.
Do your actions explain the savage beating? Are you responsible for doing something so stupid that you had to have known would result in that beating? Yeah. I mean if you smashed your face into a wall the resulting pain is obviously your fault. So just because this person has free will and might have gone against everything you knew about them and not hit you, you're free from blame? I don't think so.
But I also don't think blame is a zero-sum game, and a person is completely responsible for their own actions. That marine I made up should seriously get some counseling when they get out of jail.
I guess not! That's neat.
* reconstrucive. Or maybe both. *shrug*
Plastic surgery was originally developed to repair damage by accident, injury or disease.
And still is, called restorative plastic surgery, as opposed to cosmetic which is the more common and commonly known type today.
In high school, I saw a slideshow presentation by a restorative plastic surgeon. It was like 80 slides of 3rd degree burns, skin grafts, feet caught in paper shredders, and on and on. One of the first slides was a little girl who'd been hit in the face by a tire kicked off by an accident on the other side of the road. You could see her teeth through her cheek.
Several students threw up.
I have no idea what they were thinking. Other than convincing the "pre-med" students to find another major when they went to college. But why did the rest of us have to watch?
I don't remember ever stopping picking on Nike. But when the court ruled that they were allowed to lie in advertisements about ceasing to use sweatshops when they had not, it seems they were the winners of the PR war.
The ESA radar systems are for tracking space debris orbiting the Earth not for tracking asteroids.
Well unless the asteroids were captured by earth's gravity. :)
But yeah, detecting radio signals broadcast from earth then bounced off an asteroid would be redonculously hard. It's hard enough using the sun as our illumination.
The "even" refers to the impact, not the number, as "city killers" were used as the scary threat. They aren't scary.
So because the GGP or whoever that didn't even know what they were talking about said that, your risk analysis is limited to those types of events despite the probabilities you used not even lining up? Fine, whatever. Now think beyond that. Think about the actual problem.
In other words, probability is random. Thanks for the update.
No, in other words, instead of relying on the odds that the cards turned down are favorable to us, we should actually try to look at the cards and see what the reality is.
As it is, even finding 1% of the threats is better than nothing and not useless.
Not literally, but qualitatively yes it is. An insurance policy that covers 1% would be called useless, and correctly so, even if it doesn't literally do nothing. The difference is negligible. I don't want to treat problems in a negligible fashion.
But hey if you just meant "token" as a % of resources, then a fully-funded, vastly more effective effort would be such, like I was saying we could do that and address many other problems to. But we aren't even close to that. Because we aren't taking the problem at all seriously.
Wow, you live in a very binary world. Technology in astronomy has improved a lot over the past decades. I expect more improvements in the future.
That's rich after that last part. But so what. Our astronomy and technology is good enough now, so we should be doing it. A deadly asteroid is not going to wait until you think it's worth it.
It was an example of something that was more important, much more of an immediate threat that is being mostly ignored.
We have multiple satellites studying the sun continuously, many scientists studying the data to figure out solar weather patterns, and even solar weather predictions used to aid satellite operators and the ISS. But now we both agree that this effort is negligible and negligible is not good enough. What happened to the binary "not literally useless"?
The simple facts are that resources are limited, and should be prioritized accordingly.
Doi. And the simple facts are that if we decided to make these things priorities we could easily do both and many other things.
So, do you think we shouldn't, or do you agree that we should have an effective object discovery program?
animal version of Batman.
In order to strike fear into the hearts of animal criminals, I take the form of their worst nightmares. I am... Humanbird!