Some predictions of GR (which differ from those of Newtonian gravity) have been accurately tested -- precession of orbit of Mercury; part of the GPS calculation; decay of binary pulsar orbits, etc. There's a wikipedia page https://en.wikipedia.org/wiki/...
GR may not be perfect (and indeed, we know that either it or QM breaks down at very high energies and very small scales because they contradict, but do know that Newtonian mechanics is not correct and that in a number of experiments where GR poredictions differ from Newtonian gravity that difference is right to within a few percent.
and that paper is presumably being peer-reviewed as we speak -- hopefully an interesting debate will ensue among those who have invested the effort to understand the physics and engineering, and we will all learn something.
Regarding falsification, you are right, but also wrong. Real life is never as clearcut as the philosophy of science would like it to be. GR has already had a lot of predictions tested and they have so far not falsified it. Given that, if one experiment appeared to contradict it, the first assumption would be that the experiment or the analysis was flawed. Much effort would be spent checking it and trying to come up with independent experiments that probed the same aspects of the physics of GR. Eventually a conclusion would emerge. So more precisely it's an experiment which might have started a process that could lead to the falsification of GR, but didn't. It was interesting because it probed a part of the predictions of GR that had not previously been explored.
Er what. Firstly I said I'm NOT a gravitational wave astronomer. Secondly, what do you think I'm trying to prove by assertion? The parent asserted that LIGO couldn't work as described for reasons I wasn't really able to make sense. I mentioned some of the techniques (which are widely described on the LIGO website and in the technical literature which are used to make it work as described.
LIGO is precisely the experiment which could have falsified GR, but didn't. GR (and some other things) together predicted that there should be gravitational waves of a certain magnitude. A lot of very detailed analysis of the instrument predicted that LIGO should be able to detect them. They built LIGO and it did. Theories stand up to another test.
Rumour has it that this event was spotted early by one of the gamma-ray observing satellites (Compton, I think). They can watch all directions, although with limited resolution, and one the instruments is designed to detect short-lived high energy events quickly,
Relativity deals nicely and rather beautifully with this problem if you take the time to follow the mathematics. The key conclusion is that if something is moving at the speed of light, it is measured as doing so, relative to themselves, by EVERY inertial observer. This is very counter-intuitive, but it tests out extremely accurately in experiments.
The supernova signal is due to the time it takes the photons to get out through the remains of the exploding star. They are reabsorbed and reemitted multiple times in this jouney. The neutrinos come straight from the core and mostly escape directly.
I'm not a gravitational wave astronomer (or any other kind) but I know some physics and I am interested in the details of highly precise astronomical instruments. LIGO can, and does, measure variations in the length of the arms of the interferometer of the order of 10^-18 meters. There are many techniques needed to achieve this accuracy -- extremely stable laser sources where neither the power level nor the phase varies by much more than the inevitable statistical variation due to the beam being made up of photons; very powerful lasers so that that statistical noise is as small as possible in comparison with the total signal; the path is between very solid quartz mirrors VERY carefully suspended in a vacuum, with active damping of some vibration frequencies and active control of the mirror temperature; the beam bounces up and down the tunnels many times, so that the effective path length is longer; etc. etc.. In normal operation the paths are adjusted until the signals from the two arms precisely cancel one another out (destructive interference) and then any change in path lengths, even if only a very tiny fraction of a wavelength, shows up as a small fraction of the very powerful beams not interfering destructively, but instead being detected by a very sensitive detector, etc. etc,
It's a triumph of laser engineering and should be celebrated.
The measurement of direction depends on having three detectors spaced well apart. They compare the time of arrival of each wave pulse at the detectors and get a direction. It's not nearly accurate enough to be a single galaxy, but if there is a new very bright source of gamma rays/X-rays/... in the right general direction appearing at the right time, it's a reasonable working hypothesis that they are related.
Trees don't permanently remove CO2 from the atmosphere..
Depends what happens to the leaves when they fall and the wood when the tree dies. If if gets locked up in peat bogs or permafrost (or eventually oil or coal) you are fine. If it burns or decays, not so good. I haven't done the sums, but I suspect growing plants (I can quite believe that bamboo or something is better than trees) harvesting them and dumping them into old oil wells or coal mines, or somewhere else where they won't decay for a few millenia (what happens to woodchip in deep ocean sediment (assuming it's weighted down) does anyone know?) is more efficient than any current carbon extracting machinery we know about. Also the solar energy used to power the plants is not going directly into heat as it does when it hits desert or tarmac.
Actually most of the energy comes out as charged pions which you can direct with a magnetic field. Electrons and positrons produce gamma rays, but protons and anti-protons produce a much messier result.
For the velocities in question (say > 10% of light speed) the sail would need to be accelerated using lasers -- sunlight isn't bright enough for a large enough proportion of the journey to be useful.
For the same reason it would not get enough thrust from Proxima's light to brake to a stop (or slow down much as all) especially as Proxima is a dim red dwarf.
It might be possible to do better with a magsail, but probably better to focus on recording as much data as possible during a fly-through and then transmitting it back to Earth over the succeeding years, much along the lines of New Horizons at Pluto. With a little cunning the sail can probably serve as the main antenna.
The probe has a very stable radio transmitter on board. The dishes on Earth can get direction, distance and radial velocity easily and directly from that. The probe has cameras that can track stars accurately to establish its orientation (it's also spinning which keeps it stable). They also use the probes cameras to photgraph Jupiter its moons and selected stars to get additional information.
The position of Jupiter is known very accurately from previous missions, but New Horizons had to use its camera to refine the location of Pluto from a few million miles out to make final course corrections.
If you want to launch truly huge amounts of stuff to orbit it's very difficult to beat Orion and nuclear pulse propulsion. Politically the only way you'd see that happen would be to save the planet.
Wang bullet is cheaper -- dig a deep hole into hard rock. put a nuke at the bottom, then some padding, (sand say) then a very tough payload.
EIther the parachute opens at high speed in which case it needs to be very strong and well anchored, which makes it complicated and heavy, or it doesn't, in which case it doesn't do you much good. SpaceX don't seem to have much problem getting the stage to just above the pad at reasonably low velocity anyway, using air resistance and rockets.
That knowledge won't help us mitigate climate change,.....
It actually might. One of the problems studying climate is that we only have one planet. Exomars (and the larger endeavour of which it is part) might discover atmospheric processes at work on Mars which are important but hard to see on Earth because they are masked by something. Or something even more surprising.
Most exams can be written in a way where notes don't really help, or at least they help with things that are not important to test. Exams are supposed to verify understanding, not memorization skills. If your exam can be cheated through with mere memorization, the exam is bogus anyway - it doesn't test what it should be testing.
This is more or less true, although memorisation and recall isn't a bad proxy for understanding, since it's a lot easier to memorise and then explain a load of stuff ifit makes sense to you.
Where it gets interesting is devices with comms capability. Now your ability to solve problems in exams depends on how big and well-trained and well-equipped a support team you can muster, which mostly comes down to money.
For now the problems are solvable. Looking ahead, when every teenager has a surgically implanted (or maybe grown in situ, or even genetically engineered in) comms system in their skull, this is going to get harder. Even defining individual skill or performance, let along measuring it becomes tricky. Indeed, in extreme scenarios, even defining "individuals" becomes tricky.
Here is some data that many people don't know about. We *expect* to see natural warming as the planet climbs out of the Little Ice Age. This is corroborated by the fact that surface is warming faster than the lower tropical troposphere - which is *opposite* to the specific hypothesis of AGW.
I am all in favor of less CO2 emissions and more efficiency. I just think it is a waste of time, at this point, to make that what we throw all our money at, because it isn't going to make a bit of difference in the short term.
Do you have any evidence for this? Thousands of people who have spent their entire careers working on this disagree with you in thousands of pages of peer-reviews papers.
They can do a landing on solid ground (or at least they have done it once). Unfortunately, there is no solid ground in the right place for most flights
Slashdot Mirror
Some predictions of GR (which differ from those of Newtonian gravity) have been accurately tested -- precession of orbit of Mercury; part of the GPS calculation; decay of binary pulsar orbits, etc. There's a wikipedia page https://en.wikipedia.org/wiki/...
GR may not be perfect (and indeed, we know that either it or QM breaks down at very high energies and very small scales because they contradict, but do know that Newtonian mechanics is not correct and that in a number of experiments where GR poredictions differ from Newtonian gravity that difference is right to within a few percent.
Continuing to not find them with more sensitive instruments certainly would.
and that paper is presumably being peer-reviewed as we speak -- hopefully an interesting debate will ensue among those who have invested the effort to understand the physics and engineering, and we will all learn something.
Regarding falsification, you are right, but also wrong. Real life is never as clearcut as the philosophy of science would like it to be. GR has already had a lot of predictions tested and they have so far not falsified it. Given that, if one experiment appeared to contradict it, the first assumption would be that the experiment or the analysis was flawed. Much effort would be spent checking it and trying to come up with independent experiments that probed the same aspects of the physics of GR. Eventually a conclusion would emerge. So more precisely it's an experiment which might have started a process that could lead to the falsification of GR, but didn't. It was interesting because it probed a part of the predictions of GR that had not previously been explored.
Er what. Firstly I said I'm NOT a gravitational wave astronomer. Secondly, what do you think I'm trying to prove by assertion? The parent asserted that LIGO couldn't work as described for reasons I wasn't really able to make sense. I mentioned some of the techniques (which are widely described on the LIGO website and in the technical literature which are used to make it work as described.
LIGO is precisely the experiment which could have falsified GR, but didn't. GR (and some other things) together predicted that there should be gravitational waves of a certain magnitude. A lot of very detailed analysis of the instrument predicted that LIGO should be able to detect them. They built LIGO and it did. Theories stand up to another test.
What are you saying is not falsifiable.
Rumour has it that this event was spotted early by one of the gamma-ray observing satellites (Compton, I think). They can watch all directions, although with limited resolution, and one the instruments is designed to detect short-lived high energy events quickly,
Relativity deals nicely and rather beautifully with this problem if you take the time to follow the mathematics. The key conclusion is that if something is moving at the speed of light, it is measured as doing so, relative to themselves, by EVERY inertial observer. This is very counter-intuitive, but it tests out extremely accurately in experiments.
The supernova signal is due to the time it takes the photons to get out through the remains of the exploding star. They are reabsorbed and reemitted multiple times in this jouney. The neutrinos come straight from the core and mostly escape directly.
I'm not a gravitational wave astronomer (or any other kind) but I know some physics and I am interested in the details of highly precise astronomical instruments. LIGO can, and does, measure variations in the length of the arms of the interferometer of the order of 10^-18 meters. There are many techniques needed to achieve this accuracy -- extremely stable laser sources where neither the power level nor the phase varies by much more than the inevitable statistical variation due to the beam being made up of photons; very powerful lasers so that that statistical noise is as small as possible in comparison with the total signal; the path is between very solid quartz mirrors VERY carefully suspended in a vacuum, with active damping of some vibration frequencies and active control of the mirror temperature; the beam bounces up and down the tunnels many times, so that the effective path length is longer; etc. etc.. In normal operation the paths are adjusted until the signals from the two arms precisely cancel one another out (destructive interference) and then any change in path lengths, even if only a very tiny fraction of a wavelength, shows up as a small fraction of the very powerful beams not interfering destructively, but instead being detected by a very sensitive detector, etc. etc,
It's a triumph of laser engineering and should be celebrated.
The measurement of direction depends on having three detectors spaced well apart. They compare the time of arrival of each wave pulse at the detectors and get a direction. It's not nearly accurate enough to be a single galaxy, but if there is a new very bright source of gamma rays/X-rays/... in the right general direction appearing at the right time, it's a reasonable working hypothesis that they are related.
Trees don't permanently remove CO2 from the atmosphere. .
Depends what happens to the leaves when they fall and the wood when the tree dies. If if gets locked up in peat bogs or permafrost (or eventually oil or coal) you are fine. If it burns or decays, not so good. I haven't done the sums, but I suspect growing plants (I can quite believe that bamboo or something is better than trees) harvesting them and dumping them into old oil wells or coal mines, or somewhere else where they won't decay for a few millenia (what happens to woodchip in deep ocean sediment (assuming it's weighted down) does anyone know?) is more efficient than any current carbon extracting machinery we know about. Also the solar energy used to power the plants is not going directly into heat as it does when it hits desert or tarmac.
Actually most of the energy comes out as charged pions which you can direct with a magnetic field. Electrons and positrons produce gamma rays, but protons and anti-protons produce a much messier result.
For the velocities in question (say > 10% of light speed) the sail would need to be accelerated using lasers -- sunlight isn't bright enough for a large enough proportion of the journey to be useful.
For the same reason it would not get enough thrust from Proxima's light to brake to a stop (or slow down much as all) especially as Proxima is a dim red dwarf.
It might be possible to do better with a magsail, but probably better to focus on recording as much data as possible during a fly-through and then transmitting it back to Earth over the succeeding years, much along the lines of New Horizons at Pluto. With a little cunning the sail can probably serve as the main antenna.
The probe has a very stable radio transmitter on board. The dishes on Earth can get direction, distance and radial velocity easily and directly from that.
The probe has cameras that can track stars accurately to establish its orientation (it's also spinning which keeps it stable). They also use the probes cameras to photgraph Jupiter its moons and selected stars to get additional information.
The position of Jupiter is known very accurately from previous missions, but New Horizons had to use its camera to refine the location of Pluto from a few million miles out to make final course corrections.
Vote for governments that will stop your neighbours running those cars and pressure India and China to close their coal plants.
Your telegraph article mentions people claiming the right be forgotten. No evidence that they were granted it.
If you want to launch truly huge amounts of stuff to orbit it's very difficult to beat Orion and nuclear pulse propulsion. Politically the only way you'd see that happen would be to save the planet.
Wang bullet is cheaper -- dig a deep hole into hard rock. put a nuke at the bottom, then some padding, (sand say) then a very tough payload.
EIther the parachute opens at high speed in which case it needs to be very strong and well anchored, which makes it complicated and heavy, or it doesn't, in which case it doesn't do you much good. SpaceX don't seem to have much problem getting the stage to just above the pad at reasonably low velocity anyway, using air resistance and rockets.
Everyone has a political agenda to push. Allowing people to mine and burn coal and oil freely is also a political position.
That knowledge won't help us mitigate climate change,.....
It actually might. One of the problems studying climate is that we only have one planet. Exomars (and the larger endeavour of which it is part) might discover atmospheric processes at work on Mars which are important but hard to see on Earth because they are masked by something. Or something even more surprising.
I postulate why? Isn't there enough land to land on?
No. Or at least not in the right places.
Most exams can be written in a way where notes don't really help, or at least they help with things that are not important to test. Exams are supposed to verify understanding, not memorization skills. If your exam can be cheated through with mere memorization, the exam is bogus anyway - it doesn't test what it should be testing.
This is more or less true, although memorisation and recall isn't a bad proxy for understanding, since it's a lot easier to memorise and then explain a load of stuff ifit makes sense to you.
Where it gets interesting is devices with comms capability. Now your ability to solve problems in exams depends on how big and well-trained and well-equipped a support team you can muster, which mostly comes down to money.
For now the problems are solvable. Looking ahead, when every teenager has a surgically implanted (or maybe grown in situ, or even genetically engineered in) comms system in their skull, this is going to get harder. Even defining individual skill or performance, let along measuring it becomes tricky. Indeed, in extreme scenarios, even defining "individuals" becomes tricky.
Here is some data that many people don't know about. We *expect* to see natural warming as the planet climbs out of the Little Ice Age. This is corroborated by the fact that surface is warming faster than the lower tropical troposphere - which is *opposite* to the specific hypothesis of AGW.
Could you state that specific hypothesis please?
I am all in favor of less CO2 emissions and more efficiency. I just think it is a waste of time, at this point, to make that what we throw all our money at, because it isn't going to make a bit of difference in the short term.
Do you have any evidence for this? Thousands of people who have spent their entire careers working on this disagree with you in thousands of pages of peer-reviews papers.
The imminent "loss of ice caps" refers to arctic sea ice in summer. The winter arctic ice and the ice caps on land take much longer to melt.
They can do a landing on solid ground (or at least they have done it once). Unfortunately, there is no solid ground in the right place for most flights