I don't get what you're saying here. Even with the twins `paradox', for each twin separately, there is surely a consistent timeline. Moreover, if we have the timeline for one twin, it is possible to calculate that the timeline would be for the other (or any other observer).
Huh what? I don't know what it means to talk about space in the absence of matter, I can't see how it can even be defined. For sure the big bang has broken the symmetry of space (if there was such a thing as space independent of the big bang), so I really don't understand your response. You refer to 'space' as distinct from 'spacetime' ? Are you referring to some kind of broken Lorentz invariance, where space is translationally invariant but spacetime is not? I don't understand how that can be, it would imply that the universe is evolving in the same way at all locations in space, which then implies (as far as I can tell, in my slightly drunk state) that there would be a preferred reference frame in which this takes place (otherwise the distinction between space vs spacetime could not be made).
Yes, it is not in our past lightcone in exactly the same way that, if you were currently on Alpha Centauri, this slashdot thread would not be in your past lightcone. That doesn't change the fact that you would not be able to affect the outcome of whether I hit 'submit' or not. Sure, you would not be able to prove that the event has occurred, not for another year, but so what? It is no less certain than any other prediction of a natural event.
The timespan isn't millions of years; the time since the star started shedding nitrogen is only a few hundred years (? I can't be bothered going back to the article - but anyway it is much less than millions).
for a slightly sick analogy, predicting the lifetime of a child at birth is hard to do with any accuracy. Predicting the lifetime of someone dying of cancer is much easier;-)
Sorry, I should have said: with respect to a particular observer, we can always give a precise timeline. For a different observer the timeline might be different (eg, some events might be seen to occur in a different order), but it is still well defined.
No, even in that case Eta C has already gone supernova. It might only take you one day to get to Eta C in your frame of reference, but in the frame of reference of Eta C (or the frame of reference of the Earth, for that matter) it will take very close to 7,500 years. Since it already went nova at least 6,500 years ago, you will be at least 14,000 years too late if you wanted to see it up close.
Right - whether the center of mass is well defined depends on the geometry, I agree with that. But there certainly are geometries where it makes sense, although your example of a finite universe with positive curvature is not one of them. The infinite plane though, is not so clear. Is the universe really infinite, as opposed to finite but possibly curved? For another possible geometry, a Euclidean universe could certainly have a well-defined center of mass.
I think you are wrong here; you are thinking of time dilation effects, but unless the objects are moving very quickly with respect to each other then they are more or less in the same inertial frame of reference and there is no time dilation. The distance per se has nothing to do with it. Of course, if Eta C is moving at close to the speed of light relative to us, then it is a different story.
Are you just nitpicking? If momentum has been conserved since the big bang, then there is surely a center of mass frame, and also a center of mass. The frame in which the cosmic background is isotropic might be a better definition, because it would be well-defined even in cases where the center of mass is not (say, if the universe is finite but has a non-trivial topology), but I'd like to know your reasoning for asserting that this is indeed the case [ie. that the center of mass of the universe is not well defined].
You should RTFA. It is almost at the end of the stellar lifecycle, and has already used up all of its hydrogen. If we don't see it go nova sometime within the next 1000 years, then our theories of stellar evolution are seriously f*cked.
I wouldn't give him much credit for the discovery. The timescale doesn't need to be consistent throughout the universe, just between Earth and Eta C. And that is no problem - it is precisely analogous to communication over a slow medium (say, a war zone where your only communication from the frontline is a runner that takes half an hour to travel the distance. If you get a note saying "help, we are going to be annihilated in 10 minutes", then you don't need to use general relativity to figure that that they died already 20 minutes ago). Unless Eta C is moving at a huge velocity relative to us (ie. something close to the speed of light), the relative motion is not important. Even if Eta C WAS moving at a huge velocity, then it would still be possible to calculate the timeline accurately, you just need to be more careful about it - and it will be a slightly different timeline for a different observer.
But the inverse square law still applies, because the beams still spread out with a diameter that is proportional to distance. This applies even to the best focused laser beams; although then the spreading of the beam is very small, it is not zero and the energy density still follows the inverse square law.
Argh, I was going to moderate this thread, but when I saw this post I felt I should reply instead.
Eta C surely has gone supernova already. General relativity tells us that the passage of time depends on your movements in space, but it doesn't forbit the presence of some 'special' reference frame in which one can consistently give an age on events that happen in the universe. That special reference frame would be the one based on the center of the universe - in effect, the center of mass frame. But even without such a special frame, we can certainly give a precise timeline between any two events no matter how separated they are or how they move. General relativity allows the exact calculation, it just won't be a constant timeline with time moving at the same rate for all observers.
For the case of Eta C, it is located at a distance of 7500 lightyears away, so the light we see from it now left Eta C 7500 years ago. Since we will surely see it go supernova sometime within the next 1000 years, there is no doubt at all that Eta C went supernova sometime between 6500 and 7500 years ago. General relativity doesn't even come into it, it is already clear just from the finite velocity of light.
I don't know why my post was modded funny, it was entirely serious. Why Iwouldn't a Linux system designed for migration from a Windows platform, offer a Windows-based install?
I'm not sure about that, can you point to some examples of FOSS projects that have been shut down because of patent disputes? Since software patents are only valid in the USA (and maybe some other places, I'm not sure), they are certainly not valid in Europe, Australia, or many other places that are strong centres of FOSS development. So at worst, a patent dispute can lead to moving development of the project outside the USA. Admittedly for some projects, that might amount to killing it off anyway, but I would suggest the vast majority of FOSS projects would get on fine even if they were restricted from having a US presence.
pjviitas: I don't think the human race has any chance to creating any kind of utopia here on earth. Space is our only hope.
IWannaBeAnAC: I can't see any way space will end up as any kind of utopia.
pjviitas:What made you think that creating a utopia in space is possible?
Nothing made me think that. I was replying to your comment, where you say "Space is our only hope". My opinion is that there is no better chance of creating a utopia in space versus on Earth.
But a patent that hasn't been through a QA process is likely to be much easier to defend against.
The strategy of the patent trolls is to get a whole bunch of patents, none of them very good, but hope that maybe just one of them will stick. Fighting against a bunch of bad patents is much easier (although probably more time consuming) than fighting against a patent that has been through QA. After all, the patent troll is certain to use the fact that it has passed a peer review process to push their case.
I agree with Bruce, this is like going through your enemies ammunition supply, filtering out the duds, and leaving him with a box and a note "here is the good ammunition, come and shoot me!".
Huh? If we can't get it right down here, why should we be able to do any better in space? Already, at this early stage, a lot of the talk and actions are militaristic, how can we secure Mars before the Chinese, etc. I can't see any way space will end up as any kind of utopia.
Not really, there is no evidence that entanglement allows information transfer, nor is information transfer needed theoretically. What it does allow is non-local joint probability distributions for observables. If two parties Alice and Bob share some quantum entanglement, you can make use of this to encode a classical communication channel such that only Alice and Bob can read it (this is the basis for quantum cryptography), but the entanglement itself is not a communication channel.
Because the plants are also engineered to be resistant to chemical herbicides, so they (1) end up being grown instead of multiple, other species of the same plant, and (2) encourage a lot more herbicide use, which kills off other species of plants by `accident'.
The idea behind democracy is that there is an effective opposition to the government, that will call them to task if they attempt shenanigans like this. Government's might attempt stuff like this all the time; it is a measure of how well-functioning the democracy is as to whether they get away with it.
Trying to pass this off as 'everyone does it therefore it is OK', is WRONG! It is never OK, and the fact that the USA seems to get away with it again and again and again, is not a good indicator for the political health of that country.
"Free Speech Zones"? I'm not American, so I don't know much of your domestic history, but the first time I heard of these was only a couple of years ago.
Slashdot Mirror
I don't get what you're saying here. Even with the twins `paradox', for each twin separately, there is surely a consistent timeline. Moreover, if we have the timeline for one twin, it is possible to calculate that the timeline would be for the other (or any other observer).
Huh what? I don't know what it means to talk about space in the absence of matter, I can't see how it can even be defined. For sure the big bang has broken the symmetry of space (if there was such a thing as space independent of the big bang), so I really don't understand your response. You refer to 'space' as distinct from 'spacetime' ? Are you referring to some kind of broken Lorentz invariance, where space is translationally invariant but spacetime is not? I don't understand how that can be, it would imply that the universe is evolving in the same way at all locations in space, which then implies (as far as I can tell, in my slightly drunk state) that there would be a preferred reference frame in which this takes place (otherwise the distinction between space vs spacetime could not be made).
Yes, it is not in our past lightcone in exactly the same way that, if you were currently on Alpha Centauri, this slashdot thread would not be in your past lightcone. That doesn't change the fact that you would not be able to affect the outcome of whether I hit 'submit' or not. Sure, you would not be able to prove that the event has occurred, not for another year, but so what? It is no less certain than any other prediction of a natural event.
The timespan isn't millions of years; the time since the star started shedding nitrogen is only a few hundred years (? I can't be bothered going back to the article - but anyway it is much less than millions).
for a slightly sick analogy, predicting the lifetime of a child at birth is hard to do with any accuracy. Predicting the lifetime of someone dying of cancer is much easier ;-)
Whoa, hang on a minute. What about the big bang? Doesn't that imply that the universe cannot be infinite and translationally invariant?
Sorry, I should have said: with respect to a particular observer, we can always give a precise timeline. For a different observer the timeline might be different (eg, some events might be seen to occur in a different order), but it is still well defined.
No, even in that case Eta C has already gone supernova. It might only take you one day to get to Eta C in your frame of reference, but in the frame of reference of Eta C (or the frame of reference of the Earth, for that matter) it will take very close to 7,500 years. Since it already went nova at least 6,500 years ago, you will be at least 14,000 years too late if you wanted to see it up close.
Right - whether the center of mass is well defined depends on the geometry, I agree with that. But there certainly are geometries where it makes sense, although your example of a finite universe with positive curvature is not one of them. The infinite plane though, is not so clear. Is the universe really infinite, as opposed to finite but possibly curved? For another possible geometry, a Euclidean universe could certainly have a well-defined center of mass.
I think you are wrong here; you are thinking of time dilation effects, but unless the objects are moving very quickly with respect to each other then they are more or less in the same inertial frame of reference and there is no time dilation. The distance per se has nothing to do with it. Of course, if Eta C is moving at close to the speed of light relative to us, then it is a different story.
Are you just nitpicking? If momentum has been conserved since the big bang, then there is surely a center of mass frame, and also a center of mass. The frame in which the cosmic background is isotropic might be a better definition, because it would be well-defined even in cases where the center of mass is not (say, if the universe is finite but has a non-trivial topology), but I'd like to know your reasoning for asserting that this is indeed the case [ie. that the center of mass of the universe is not well defined].
You should RTFA. It is almost at the end of the stellar lifecycle, and has already used up all of its hydrogen. If we don't see it go nova sometime within the next 1000 years, then our theories of stellar evolution are seriously f*cked.
I wouldn't give him much credit for the discovery. The timescale doesn't need to be consistent throughout the universe, just between Earth and Eta C. And that is no problem - it is precisely analogous to communication over a slow medium (say, a war zone where your only communication from the frontline is a runner that takes half an hour to travel the distance. If you get a note saying "help, we are going to be annihilated in 10 minutes", then you don't need to use general relativity to figure that that they died already 20 minutes ago). Unless Eta C is moving at a huge velocity relative to us (ie. something close to the speed of light), the relative motion is not important. Even if Eta C WAS moving at a huge velocity, then it would still be possible to calculate the timeline accurately, you just need to be more careful about it - and it will be a slightly different timeline for a different observer.
But the inverse square law still applies, because the beams still spread out with a diameter that is proportional to distance. This applies even to the best focused laser beams; although then the spreading of the beam is very small, it is not zero and the energy density still follows the inverse square law.
Argh, I was going to moderate this thread, but when I saw this post I felt I should reply instead.
Eta C surely has gone supernova already. General relativity tells us that the passage of time depends on your movements in space, but it doesn't forbit the presence of some 'special' reference frame in which one can consistently give an age on events that happen in the universe. That special reference frame would be the one based on the center of the universe - in effect, the center of mass frame. But even without such a special frame, we can certainly give a precise timeline between any two events no matter how separated they are or how they move. General relativity allows the exact calculation, it just won't be a constant timeline with time moving at the same rate for all observers.
For the case of Eta C, it is located at a distance of 7500 lightyears away, so the light we see from it now left Eta C 7500 years ago. Since we will surely see it go supernova sometime within the next 1000 years, there is no doubt at all that Eta C went supernova sometime between 6500 and 7500 years ago. General relativity doesn't even come into it, it is already clear just from the finite velocity of light.
I don't know why my post was modded funny, it was entirely serious. Why Iwouldn't a Linux system designed for migration from a Windows platform, offer a Windows-based install?
Does it use a Windows-based installer?
I'm not sure about that, can you point to some examples of FOSS projects that have been shut down because of patent disputes? Since software patents are only valid in the USA (and maybe some other places, I'm not sure), they are certainly not valid in Europe, Australia, or many other places that are strong centres of FOSS development. So at worst, a patent dispute can lead to moving development of the project outside the USA. Admittedly for some projects, that might amount to killing it off anyway, but I would suggest the vast majority of FOSS projects would get on fine even if they were restricted from having a US presence.
I think we need some context here.
Nothing made me think that. I was replying to your comment, where you say "Space is our only hope". My opinion is that there is no better chance of creating a utopia in space versus on Earth.
But a patent that hasn't been through a QA process is likely to be much easier to defend against.
The strategy of the patent trolls is to get a whole bunch of patents, none of them very good, but hope that maybe just one of them will stick. Fighting against a bunch of bad patents is much easier (although probably more time consuming) than fighting against a patent that has been through QA. After all, the patent troll is certain to use the fact that it has passed a peer review process to push their case.
I agree with Bruce, this is like going through your enemies ammunition supply, filtering out the duds, and leaving him with a box and a note "here is the good ammunition, come and shoot me!".
Huh? If we can't get it right down here, why should we be able to do any better in space? Already, at this early stage, a lot of the talk and actions are militaristic, how can we secure Mars before the Chinese, etc. I can't see any way space will end up as any kind of utopia.
Well, don't happen often anyway. I would suggest that the USA has more school massacres than the rest of the world put together.
Not really, there is no evidence that entanglement allows information transfer, nor is information transfer needed theoretically. What it does allow is non-local joint probability distributions for observables. If two parties Alice and Bob share some quantum entanglement, you can make use of this to encode a classical communication channel such that only Alice and Bob can read it (this is the basis for quantum cryptography), but the entanglement itself is not a communication channel.
Because the plants are also engineered to be resistant to chemical herbicides, so they (1) end up being grown instead of multiple, other species of the same plant, and (2) encourage a lot more herbicide use, which kills off other species of plants by `accident'.
The idea behind democracy is that there is an effective opposition to the government, that will call them to task if they attempt shenanigans like this. Government's might attempt stuff like this all the time; it is a measure of how well-functioning the democracy is as to whether they get away with it.
Trying to pass this off as 'everyone does it therefore it is OK', is WRONG! It is never OK, and the fact that the USA seems to get away with it again and again and again, is not a good indicator for the political health of that country.
"Free Speech Zones"? I'm not American, so I don't know much of your domestic history, but the first time I heard of these was only a couple of years ago.