This is an experiment designed to test the correction due to General Relativity of the thomas precession of a tiny spinning sphere.
The correction to the precession will be on the order of arcseconds (1/3600 of a degree) per year.
There are some very good general relativists who have very severe reservations about this project. If they do detect a signal, I suspect it will be more of a testament to the power of experimental precision rather than a test of GR, which practically every serious physicist believes to be correct.
It's also worth noting that if nothing is seen, it's more likely than not due to the difficulty of detecting such a small signal.
I think this is an absurd way of viewing this problem.
To Wal-Mart -- they're the biggest retailer in the US because they undersell every other retailer. They're a large conglomoration and buy in bulk. Why? Because capitalism tends to favor the one cheapest run company with acceptable quality goods.
How else do you explain the success of Britney Spears?
I think the biggest reason wal-mart is so successful is that people are either uninformed as to their business practices, or they don't care about anything more than their own bottom line.
As to the US auto industry, that's an entirely different story. You've got the high-cost, low-quality part right. The fact that instead of re-engineering their vehicles and their companies strategies, they took the laziest way out to reduce cost, and went overseas. Hence Roger and Me etc...
Perhaps if there were some way of capturing people's imagination (i.e. capturing people like Paul Allen's or other bajillionaires imaginations), more private people would invest in natural science?
Private corporations sure aren't going to do it anymore -- look at the demise of pure science at Bell Labs.
This is perhaps something positive on multiple fronts... with the potential to grow the investment of wealthy individuals into research science, if it's advertised correctly.
How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not. Pluto, BTW, Sedna, and many of the largest moons can all do this.
I also think, for the record, that if something as large as Luna, or Titan, or Europa were out floating in space orbiting the sun and not another planet, they would be considered planets too.
There are many astronomy/aerospace missions that need to get above the bulk of the atmosphere. For science, having a controlled station at an altitude of 70,000 feet would be wonderful.
Now, in addition to all the cool cosmic ray stuff that could be done up there, putting a near-space telescope up there would be a wonderful (and relatively cheap) idea... any thought of other scientific (rather than solely comm satellite) uses for this?
But the point is...?
on
Melting Europa
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· Score: 5, Interesting
As a graduate student in astrophysics (not planetary geology, which this would fall under), I think this is an overall good idea. (Agreed, the poster sounds a tad biased.)
There are a few points which I would like clarified by someone who is perhaps knowledgeable. For one, landing a spacecraft on Europa, where we have little knowledge of its atmospheric conditions, will be a formidable challenge. (We've lost many Mars-intended missions due to that.) How can we plan for that?
Secondly, I don't think it's known how deep the ice goes? Is there a plan for if the ice is a foot thick? How about 10 feet? How about 1000?
Next, can we still transmit a signal back if we have to take a probe that far underwater?
Notwithstanding a Europan shark eating the probe, I think there are some serious scientific reasons to be concerned about the search for life on one of the solar system's most likely candidates -- and we should ask ourselves if we're taking the best approach for a multi-hundred-million dollar mission?
You're absolutely right. If the third derivative is negative, or higher derivatives affect physics, this would change things again. Or, as you say, if there is some potential that is chosen, you can construct whatever universe you like.
This second idea is actually the basis of quintessence, one of the leading theories of dark energy. But there is no motivation for choosing these potentials, which is why many physicists find them unsatisfactory.
The problem with your reasoning for higher derivative physics is, well, physics just doesn't seem to depend on higher derivatives. Newton's law is F=ma. It could have been F=ma + something*(da/dt), but it appears physics doesn't work that way. There are stability arguments people have used to "disprove" that physics depends on anything higher than second derivatives, actually.
(I put disprove in quotes not because it isn't right, but because I don't understand the arguments well enough to know whether it's right or not. But it's still an excellent point.)
Physicists generally write down equations for the scale factor, it's first derivative, and it's second derivative. Higher derivatives do exist and can be written down, but the general consensus is that there is no new physical information in there.
If you fear things involving physics, skip the rest of this post.
Alright, for those who are interested, it seems like 70% of the current energy density of the universe is in some form of "dark energy", as was previously stated. The Universe is currently 13.7 billion years old.
We say that every component in the universe has an energy density and a pressure. Dark energy is different from things like normal matter and light, because these have positive pressures. (Normal matter has a very small pressure). But dark energy has a negative pressure, which means it works opposite to gravity.
Everything that has a pressure that we can physically think of (well, that I can physically think of) has a pressure between (-1)*energy density and (+1)*energy density. A big rip will only occur (and it will only occur in the very distant future) if the dark energy has a pressure that is outside this range, such that pressure is less than (-1)*energy density.
This is, of course, possible, but unlikely in my view.
wouldnt it be obvious to build another, better Hubble-like telescope and attach it to the ISS
I don't know if this idea has been considered, but what is commonly referred to as the "successor" to Hubble (I'll explain below why it's not), the James Webb Space Telescope, is built so that it won't need servicing missions.
Hubble was built to be upgraded, as it's great seeing power comes from not having to look through an atmosphere and from having great cameras. (The cameras are what gets upgraded and replaced.)
It is designed to view objects in the Ultraviolet and Blue light range. James Webb only "sees" in the Red and Infrared, and therefore isn't a replacement, it's just a different telescope.
The only thing I wonder about, that may make this a bad idea, is that I believe the ISS may not be in a high enough orbit to house a telescope -- someone may want to check this.
We'd all like the government to provide for science. As an astrophysics student at a government-funded university, I certainly think it should be the government's job.
But our society doesn't always do that. Back in the 1960's, it wasn't the government that ran the show for science, though. Who discovered the Cosmic Microwave Background? Penzias and Wilson, two Bell-Labs scientists.
My point is that, if some time ago private industry felt an obligation to science to "give back" to the scientific world that they got rich off of, maybe they ought to be encouraged to do it again...
You`ve hit the common misperception with this plan-- it does not increase the NASA budget drastically. Rather, it reassigns funds within the current budget, adding around 10% to the total.
I strongly disagree that the "reassignment" of funds is at all productive.
Over the past 10 years or so, NASA has developed a "faster, better, cheaper" strategy, which has allowed for a myriad of small-ish projects to proceed and allow for vast growth in all sorts of fields of science.
This includes planetary geology, solar physics, Mars/Mercury/Venus/asteroid exploration, as well as larger cosmological issues, through (telescope-type) missions like Chandra, XMM-Newton, Hubble Space Telescope, etc.
If you're only going to reassign funds and slightly increase the budget, what's going to happen to missions like these, that actually teach us about the world we live in? I think to put a man on Mars is a great goal, but are we prepared to gut all the other programs like this to accomplish that goal? As an astrophysics graduate student, I am not.
Jerf (below in thread) got the jist of this, that there are a lot of independent reasons to believe in dark matter of some form.
Protons, neutrons, and electrons, what we commonly refer to as "normal" or "baryonic" matter, make up 4.4% of the critical density of the universe. We know this from one of the cornerstones of the big bang theory, the part called nucleosynthesis. This predicts the abundances of Helium-4, Helium-3, Deuterium, and Lithium-7, which is highly consistent with observations. (Incidentally, the book "The first three minutes" gives an excellent popular account of this.)
This matter (which is where the "MACHO" theory comes from, btw) is insufficient to explain many observations, such as:
1) Galactic rotation curves. Spiral galaxies have FLAT rotation curves, which means the angular velocities stay the same all the way out. This means that either there is dark matter in the shape of a disk or halo, or the law of gravity is wrong.
2) Velocities of galaxies in clusters. These galaxies move faster than the escape velocities based on baryons alone, therefore, they wouldn't cluster like this. Either there is more mass in there (dark matter) in the shape of a spherical halo, or the law of gravity is wrong (in a different way from #1).
3) Cosmological parameters: From Supernova and Cosmic microwave background data combined, we know that the universe is about 30% composed of matter. (Incidentally, someone asked what % is photons. The answer is 0.018%)
30% is much greater than 4.4%, and therefore there really ought to be something else. If you want to try to modify gravity (and many people do, Philip Mannheiem at UConn is one of the more famous ones to try), you need to do it in a fashion that keeps all the predictions of General Relativity intact. So far, no theory does that. They have made theories that explain galactic rotation curves, but they fail when it comes to relativistic bending of light, etc.
Sorry for the length of this, but I believe the evidence for Dark Matter is overwhelming...
It's more than that.
If Dark Matter doesn't exist, we will be forced to re-examine more than just our current picture of the universe. Galactic Rotation curves, velocity dispersions of galaxy clusters, the flatness of the universe implied by the CMB, type Ia supernovae data, as well as other distance indicators, all imply that the parameter "Omega_mass" (the mass density of the universe divided by the critical density) is about 0.3.
If there is no "dark matter", we don't know how to explain this number. Baryons, i.e. stars, planets, gas, etc., make up only an "Omega" of 0.044 +/- 0.009. This constraint is from Big Bang Nucleosynthesis and is very strong. Although there are plenty of open questions about dark matter, it seems to me (just an astrophysics grad student) that there is an overwhelming amount of evidence for not only dark matter, but the model of "cold" dark matter as well.
None of the alternatives can explain even half of what Dark Matter can, including modifying gravity. Plus, Dark Matter is consistent with GR, the big bang, and everything else we hold dear about physics and astronomy, whereas other theories don't.
Just my two cents...
Ethan
Was anyone else horrified to read that this "$12 billion program" is only going to cause an increase in the NASA budget of $1 billion? As a strong supporter of all the recent advances in cosmology and observational data, this greatly concerns me and others in my field. Does this mean that $11 billion which would be otherwise spent on exploring the cosmos is now going to be redirected to funding a long-range plan that will need countless presidents and congresses to approve it?
Slashdot Mirror
This is an experiment designed to test the correction due to General Relativity of the thomas precession of a tiny spinning sphere.
The correction to the precession will be on the order of arcseconds (1/3600 of a degree) per year.
There are some very good general relativists who have very severe reservations about this project. If they do detect a signal, I suspect it will be more of a testament to the power of experimental precision rather than a test of GR, which practically every serious physicist believes to be correct.
It's also worth noting that if nothing is seen, it's more likely than not due to the difficulty of detecting such a small signal.
I wonder how much terrain these rovers can explore in 5 months, or if they're basically useless because of range limitations?
I think this is an absurd way of viewing this problem.
To Wal-Mart -- they're the biggest retailer in the US because they undersell every other retailer. They're a large conglomoration and buy in bulk. Why? Because capitalism tends to favor the one cheapest run company with acceptable quality goods.
How else do you explain the success of Britney Spears?
I think the biggest reason wal-mart is so successful is that people are either uninformed as to their business practices, or they don't care about anything more than their own bottom line.
As to the US auto industry, that's an entirely different story. You've got the high-cost, low-quality part right. The fact that instead of re-engineering their vehicles and their companies strategies, they took the laziest way out to reduce cost, and went overseas. Hence Roger and Me etc...
What sort of responsibility to create jobs should a company have to the nation that purchases/has a demand for the goods they're producing?
(Link to Article)
Perhaps if there were some way of capturing people's imagination (i.e. capturing people like Paul Allen's or other bajillionaires imaginations), more private people would invest in natural science? Private corporations sure aren't going to do it anymore -- look at the demise of pure science at Bell Labs. This is perhaps something positive on multiple fronts... with the potential to grow the investment of wealthy individuals into research science, if it's advertised correctly.How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not. Pluto, BTW, Sedna, and many of the largest moons can all do this.
I also think, for the record, that if something as large as Luna, or Titan, or Europa were out floating in space orbiting the sun and not another planet, they would be considered planets too.
There are many astronomy/aerospace missions that need to get above the bulk of the atmosphere. For science, having a controlled station at an altitude of 70,000 feet would be wonderful.
Now, in addition to all the cool cosmic ray stuff that could be done up there, putting a near-space telescope up there would be a wonderful (and relatively cheap) idea... any thought of other scientific (rather than solely comm satellite) uses for this?
As a graduate student in astrophysics (not planetary geology, which this would fall under), I think this is an overall good idea. (Agreed, the poster sounds a tad biased.)
There are a few points which I would like clarified by someone who is perhaps knowledgeable. For one, landing a spacecraft on Europa, where we have little knowledge of its atmospheric conditions, will be a formidable challenge. (We've lost many Mars-intended missions due to that.) How can we plan for that?
Secondly, I don't think it's known how deep the ice goes? Is there a plan for if the ice is a foot thick? How about 10 feet? How about 1000?
Next, can we still transmit a signal back if we have to take a probe that far underwater?
Notwithstanding a Europan shark eating the probe, I think there are some serious scientific reasons to be concerned about the search for life on one of the solar system's most likely candidates -- and we should ask ourselves if we're taking the best approach for a multi-hundred-million dollar mission?
You're absolutely right. If the third derivative is negative, or higher derivatives affect physics, this would change things again. Or, as you say, if there is some potential that is chosen, you can construct whatever universe you like.
This second idea is actually the basis of quintessence, one of the leading theories of dark energy. But there is no motivation for choosing these potentials, which is why many physicists find them unsatisfactory.
The problem with your reasoning for higher derivative physics is, well, physics just doesn't seem to depend on higher derivatives. Newton's law is F=ma. It could have been F=ma + something*(da/dt), but it appears physics doesn't work that way. There are stability arguments people have used to "disprove" that physics depends on anything higher than second derivatives, actually.
(I put disprove in quotes not because it isn't right, but because I don't understand the arguments well enough to know whether it's right or not. But it's still an excellent point.)
Physicists generally write down equations for the scale factor, it's first derivative, and it's second derivative. Higher derivatives do exist and can be written down, but the general consensus is that there is no new physical information in there.
If you fear things involving physics, skip the rest of this post. Alright, for those who are interested, it seems like 70% of the current energy density of the universe is in some form of "dark energy", as was previously stated. The Universe is currently 13.7 billion years old. We say that every component in the universe has an energy density and a pressure. Dark energy is different from things like normal matter and light, because these have positive pressures. (Normal matter has a very small pressure). But dark energy has a negative pressure, which means it works opposite to gravity. Everything that has a pressure that we can physically think of (well, that I can physically think of) has a pressure between (-1)*energy density and (+1)*energy density. A big rip will only occur (and it will only occur in the very distant future) if the dark energy has a pressure that is outside this range, such that pressure is less than (-1)*energy density. This is, of course, possible, but unlikely in my view.
We'd all like the government to provide for science. As an astrophysics student at a government-funded university, I certainly think it should be the government's job.
But our society doesn't always do that. Back in the 1960's, it wasn't the government that ran the show for science, though. Who discovered the Cosmic Microwave Background? Penzias and Wilson, two Bell-Labs scientists.
My point is that, if some time ago private industry felt an obligation to science to "give back" to the scientific world that they got rich off of, maybe they ought to be encouraged to do it again...
I'll try to translate.
Jerf (below in thread) got the jist of this, that there are a lot of independent reasons to believe in dark matter of some form.
Protons, neutrons, and electrons, what we commonly refer to as "normal" or "baryonic" matter, make up 4.4% of the critical density of the universe. We know this from one of the cornerstones of the big bang theory, the part called nucleosynthesis. This predicts the abundances of Helium-4, Helium-3, Deuterium, and Lithium-7, which is highly consistent with observations.
(Incidentally, the book "The first three minutes" gives an excellent popular account of this.)
This matter (which is where the "MACHO" theory comes from, btw) is insufficient to explain many observations, such as:
1) Galactic rotation curves. Spiral galaxies have FLAT rotation curves, which means the angular velocities stay the same all the way out. This means that either there is dark matter in the shape of a disk or halo, or the law of gravity is wrong.
2) Velocities of galaxies in clusters. These galaxies move faster than the escape velocities based on baryons alone, therefore, they wouldn't cluster like this. Either there is more mass in there (dark matter) in the shape of a spherical halo, or the law of gravity is wrong (in a different way from #1).
3) Cosmological parameters: From Supernova and Cosmic microwave background data combined, we know that the universe is about 30% composed of matter. (Incidentally, someone asked what % is photons. The answer is 0.018%)
30% is much greater than 4.4%, and therefore there really ought to be something else. If you want to try to modify gravity (and many people do, Philip Mannheiem at UConn is one of the more famous ones to try), you need to do it in a fashion that keeps all the predictions of General Relativity intact. So far, no theory does that. They have made theories that explain galactic rotation curves, but they fail when it comes to relativistic bending of light, etc.
Sorry for the length of this, but I believe the evidence for Dark Matter is overwhelming...
It's more than that. If Dark Matter doesn't exist, we will be forced to re-examine more than just our current picture of the universe. Galactic Rotation curves, velocity dispersions of galaxy clusters, the flatness of the universe implied by the CMB, type Ia supernovae data, as well as other distance indicators, all imply that the parameter "Omega_mass" (the mass density of the universe divided by the critical density) is about 0.3. If there is no "dark matter", we don't know how to explain this number. Baryons, i.e. stars, planets, gas, etc., make up only an "Omega" of 0.044 +/- 0.009. This constraint is from Big Bang Nucleosynthesis and is very strong. Although there are plenty of open questions about dark matter, it seems to me (just an astrophysics grad student) that there is an overwhelming amount of evidence for not only dark matter, but the model of "cold" dark matter as well. None of the alternatives can explain even half of what Dark Matter can, including modifying gravity. Plus, Dark Matter is consistent with GR, the big bang, and everything else we hold dear about physics and astronomy, whereas other theories don't. Just my two cents... Ethan
Was anyone else horrified to read that this "$12 billion program" is only going to cause an increase in the NASA budget of $1 billion? As a strong supporter of all the recent advances in cosmology and observational data, this greatly concerns me and others in my field. Does this mean that $11 billion which would be otherwise spent on exploring the cosmos is now going to be redirected to funding a long-range plan that will need countless presidents and congresses to approve it?