Can you givemore information on these experiments? Particles with imagenary mass would be very interesting, because according to relativity theory they would always travel faster than light (much as `normal' always moves slower than light). Discovery of tachyons would be something to see.
Also, remember that Newton's laws only apply at low speeds compared to c. This makes it difficult to use them to predict anything about tachyons.
How? In order to really swallow things up,a black hole must have i) a radius roughly equal to the object to be swallowed or ii) enough mass to pull a missile from its trajectory and then swallow it. The problem with i) is that you don't want a black hole of that size anywhere near your planet (a black hole with a horizon size of 1 inch has a mass equal to the earth's). The problem with ii) is that more or less the same: the black hole should be very massive in order to do this, only very massive objects have a chance of pulling missiles away. The dangers of having a massive (well, not in astronomical terms, but you get my drift) black hole near the earth are left as an exercise to the reader.
Don't you mean (1 - 8.3e-19) ^ 1e11? I mean, assuming each potential collision is an independant, random event.
Yeah, that's true, but it didn't fit on my calculator, so I gave a reasonable approximation. And the collisions are not totally random, but I'd hate to do the math on that (that's why we have supercomputers, right?:-).
But the sight will be something, provided you are on a dark enough spot (remember, in most populated places you can even see the milky way due to scattered light, and that's the galaxy we're in!)
Let's do a quick calculation here: The radius of the sun (a nice average model star) is about 700,000 km, so its cross section is 1.5e12 km^2.
Let's enlarge the effective cross section for a bit to include the effects of gravity (stars attract eachother, so there's more chance that they will collide) to a nice, round 1e13 km^2.
There are approximately 1e11 stars in the galaxy, so the total cross section of stars is 1e24 km^2.
The radius of the galaxy is about 20 kpc, the total area of the galaxy is 1300 kpc^2 = 1.2e42 km^2, so the total fraction of the area of the galaxy that contains stars is 8.3e-19. the chance that none of the 1e11 stars in Andromeda will collide with one of "our" stars is approximately
1 - (1e11 x 8.3e-19) = 1 - 8.3e-8, very close to 1. I'll take my chances.
The main danger, if I recall correctly, comes from colliding gas clouds. These are much bigger than stars, and about as common, so the chances this will happen are far greater. Colliding gas clouds tend to form stars, as their densities suddenly increase due to the shock, and some of those stars will be super massive ones that go supernova in a few million years. A supernova right nextdoor (on an astronomical scale, at least) is not something you want to happen, believe me.
Okay, you're right. Optical astronomy isn't exactly my strong point... But I should have remembered cosmics.
But doesn't the point still stand that HDF could only be done from outer space? IIRC even the night sky isn't dark enough to see really faint objects. And of course there's seeing to consider...
Ah, thanks. I couldn't think of a mechanism that would keep ratios between isotopes constant, but I see that the ratio is assumed to be constant in magma, so the age of a rock can be determined.
Which goes to show that I should read up in geology.
What annoys me about the Hubble "money pit" is that it offers no advantages over cheaper, land based telescopes that we have had access to for centuries. I am not saying that being curious about Gods creation is wrong, but we can only see that which God allows us to see. Hubble has not shown us anything new in the eleven years that it has been in orbit. All it has managed to do is suck up tax payers money at a huge rate.
Says who? Ask any astronomer out there about Hubble, and you will hear enthusiastic stories about the sharpest pictures ever made with a telescope (because there is no turbulent atmosphere there), the wonderful thing that is called the Hubble Deep Field (48 hours of exposure of one piece of sky; try doing that with a ground based telescope), and what a pity it is that it's merely a 2.5 metre telescope instead of a 8 metre one (yes, this comment was actually heard at an astronomical conference some years ago). And of course how everyone is looking forward to the NGST (next generation space telescope), which will have a diameter of 8 metres.
So please get your facts right before you make a fool of yourself on Slashdot. Not that many people seem to mind...
How do biologists know what level of carbon dating is how old? Well, the geologist over there says the rock it was found in is x million years old. So ask the geologist how he knows how old the rock is. Well, of course, fossils just that old happen to be found there, so of course the rock
is that old!
The short answer is no.
The slightly longer answer is that you take a bunch of carbon-14, measure how many of those atoms decay in a given time period and from there deduce the half life of carbon 14. Then, observing that most plants have steady ratios of C-14 over C-12 (the stable and most common isotope), one can determine the age of plant remains from their C-14 content.
Since C-14 has a half life of 5730 years, it is not very difficult to show that some plant samples are older than the proposed 6000 years of earth existence creationists claim.
This method cannot be used to date animal parts, let alone dinosaur bones (after a couple of thousand half lives there's remarkably little C-14 left:-). IANAA (I am not an archeologist), so I don't know how these things are dated.
Light (in vacuum) moves along a null-geodesic in (not necessarily curved) space-time. The null geodesic part means that the distance a lightray travels in time dt equals c dt. In other words, the speed (used in its everyday definition, just distance divided by time) of light in vacuum is constant and equal to c. This means it is impossible to stop light from travelling in vacuum. On the other hand, if you beam llight through a dense medium, it moves at a velocity slower than c, I read an article some months ago (no references, I don't remember where) that a research team slowed it down to below walking pace. This is what the article is all about (at least, that's what i understand from it).
A time frame cannot be said to be moving; in relativity one usually takes a fixed coordinate system with one of the axes conveniently named "time", but all particles moving in that system also have their own "eigentime", which is the time you would read from a clock carried by that particle.
It may be interesting to note here that for light (and any other phenomenon travelling with the speed of light) there is no proper definition for the eigentime, you can always multiply it by a constant factor and things work out the same. Thus, time can be said to "stand still" on a lightray.
Re:Artificial Black Holes
on
Stop, Light.
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· Score: 1
From what I gather from the article, the light wave is dimmed (effectively destryed) and its information is stored in the gas. When a second lightray is sent through the gas, it takes on the properties on the wave.
I don't know the article you are referring to, but normally to create a black hole you have to have some pretty extreme circumstances (like the mass of a small mountain (or its equivalent in energy) packed into the volume of a hydrogen atom), this
is far beyond anything possible in modern laboratories.
Magnetic fields aren't nearly as important as a strong gravitational field. Small planets close to the sun (thus having a hot atmosphere) lose light molecules because their velocity exceeds the escape velocity of the planet. IIRC mars can just keep carbondioxide and oxygen, but not water, methane and lighter gases, but even CO2 and oxygen leak away slowly.
If you ever want to live on mars, a magnetic field may be convenient to keep fast charged particles from reaching the surface. They're great for causing mutations and other nasty things.
I mean, what is it with all of the different particles that these people seem to want to invent at every opportunity? Higgs bosons,technicolor particles, partons, selectrons, squarks, winos, zinos and dinos, they're all on the same scientific level as evolution - a piece of
pseudo-science that cannot be proven by experiment. And as far as I knew, if it can't be proved by experiment, it isn't science at all.
A lot of these particles were actually "invented" to make theoretical physics agree with experiments. A good example is the neutrino: its existence was first postulated in the 1930s to account for the conservation of energy in beta-decay (without neutrinoes, a little energy was missing), and since then a lot of experiments have been done that confirm their presence. In the case of Higgs bosons, squarks and the like, these particles were postulated to keep theory in accordance with other experimental data (like particles having mass, and the existance of gravity). But having a theory that works doesn't automatically mean it's true, and that's why people like to observe these particles in an experiment. A confirmation of the theory would be nice, while proof that the theory is wrong would make people come up with a new theory that does agree with experiments.
Slashdot Mirror
How nice, they brought a cave troll...
Can you givemore information on these experiments? Particles with imagenary mass would be very interesting, because according to relativity theory they would always travel faster than light (much as `normal' always moves slower than light). Discovery of tachyons would be something to see.
Also, remember that Newton's laws only apply at low speeds compared to c. This makes it difficult to use them to predict anything about tachyons.
How? In order to really swallow things up,a black hole must have i) a radius roughly equal to the object to be swallowed or ii) enough mass to pull a missile from its trajectory and then swallow it. The problem with i) is that you don't want a black hole of that size anywhere near your planet (a black hole with a horizon size of 1 inch has a mass equal to the earth's). The problem with ii) is that more or less the same: the black hole should be very massive in order to do this, only very massive objects have a chance of pulling missiles away. The dangers of having a massive (well, not in astronomical terms, but you get my drift) black hole near the earth are left as an exercise to the reader.
Wow, a remotely funny beowulf cluster joke. What is the world coming to?
- Mute
Don't you mean (1 - 8.3e-19) ^ 1e11? I mean, assuming each potential collision is an independant, random event.
:-).
Yeah, that's true, but it didn't fit on my calculator, so I gave a reasonable approximation. And the collisions are not totally random, but I'd hate to do the math on that (that's why we have supercomputers, right?
But the sight will be something, provided you are on a dark enough spot (remember, in most populated places you can even see the milky way due to scattered light, and that's the galaxy we're in!)
- Mute
Let's do a quick calculation here: The radius of the sun (a nice average model star) is about 700,000 km, so its cross section is 1.5e12 km^2. Let's enlarge the effective cross section for a bit to include the effects of gravity (stars attract eachother, so there's more chance that they will collide) to a nice, round 1e13 km^2. There are approximately 1e11 stars in the galaxy, so the total cross section of stars is 1e24 km^2. The radius of the galaxy is about 20 kpc, the total area of the galaxy is 1300 kpc^2 = 1.2e42 km^2, so the total fraction of the area of the galaxy that contains stars is 8.3e-19. the chance that none of the 1e11 stars in Andromeda will collide with one of "our" stars is approximately 1 - (1e11 x 8.3e-19) = 1 - 8.3e-8, very close to 1. I'll take my chances.
The main danger, if I recall correctly, comes from colliding gas clouds. These are much bigger than stars, and about as common, so the chances this will happen are far greater. Colliding gas clouds tend to form stars, as their densities suddenly increase due to the shock, and some of those stars will be super massive ones that go supernova in a few million years. A supernova right nextdoor (on an astronomical scale, at least) is not something you want to happen, believe me.
- Kite
Okay, you're right. Optical astronomy isn't exactly my strong point... But I should have remembered cosmics.
But doesn't the point still stand that HDF could only be done from outer space? IIRC even the night sky isn't dark enough to see really faint objects. And of course there's seeing to consider...
Ah, thanks. I couldn't think of a mechanism that would keep ratios between isotopes constant, but I see that the ratio is assumed to be constant in magma, so the age of a rock can be determined.
Which goes to show that I should read up in geology.
What annoys me about the Hubble "money pit" is that it offers no advantages over cheaper, land based telescopes that we have had access to for centuries. I am not saying that being curious about Gods creation is wrong, but we can only see that which God allows us to see. Hubble has not shown us anything new in the eleven years that it has been in orbit. All it has managed to do is suck up tax payers money at a huge rate.
Says who? Ask any astronomer out there about Hubble, and you will hear enthusiastic stories about the sharpest pictures ever made with a telescope (because there is no turbulent atmosphere there), the wonderful thing that is called the Hubble Deep Field (48 hours of exposure of one piece of sky; try doing that with a ground based telescope), and what a pity it is that it's merely a 2.5 metre telescope instead of a 8 metre one (yes, this comment was actually heard at an astronomical conference some years ago). And of course how everyone is looking forward to the NGST (next generation space telescope), which will have a diameter of 8 metres.
So please get your facts right before you make a fool of yourself on Slashdot. Not that many people seem to mind...
All I ask is that you stop and think.
All I ask is that you heed your own advice.
How do biologists know what level of carbon dating is how old? Well, the geologist over there says the rock it was found in is x million years old. So ask the geologist how he knows how old the rock is. Well, of course, fossils just that old happen to be found there, so of course the rock is that old!
:-). IANAA (I am not an archeologist), so I don't know how these things are dated.
The short answer is no.
The slightly longer answer is that you take a bunch of carbon-14, measure how many of those atoms decay in a given time period and from there deduce the half life of carbon 14. Then, observing that most plants have steady ratios of C-14 over C-12 (the stable and most common isotope), one can determine the age of plant remains from their C-14 content.
Since C-14 has a half life of 5730 years, it is not very difficult to show that some plant samples are older than the proposed 6000 years of earth existence creationists claim.
This method cannot be used to date animal parts, let alone dinosaur bones (after a couple of thousand half lives there's remarkably little C-14 left
Thank you, I couldn't find the link.
any physicists out there?
An astrophysicist actually...
Okay, here goes:
Light (in vacuum) moves along a null-geodesic in (not necessarily curved) space-time. The null geodesic part means that the distance a lightray travels in time dt equals c dt. In other words, the speed (used in its everyday definition, just distance divided by time) of light in vacuum is constant and equal to c. This means it is impossible to stop light from travelling in vacuum. On the other hand, if you beam llight through a dense medium, it moves at a velocity slower than c, I read an article some months ago (no references, I don't remember where) that a research team slowed it down to below walking pace. This is what the article is all about (at least, that's what i understand from it).
A time frame cannot be said to be moving; in relativity one usually takes a fixed coordinate system with one of the axes conveniently named "time", but all particles moving in that system also have their own "eigentime", which is the time you would read from a clock carried by that particle.
It may be interesting to note here that for light (and any other phenomenon travelling with the speed of light) there is no proper definition for the eigentime, you can always multiply it by a constant factor and things work out the same. Thus, time can be said to "stand still" on a lightray.
From what I gather from the article, the light wave is dimmed (effectively destryed) and its information is stored in the gas. When a second lightray is sent through the gas, it takes on the properties on the wave.
I don't know the article you are referring to, but normally to create a black hole you have to have some pretty extreme circumstances (like the mass of a small mountain (or its equivalent in energy) packed into the volume of a hydrogen atom), this is far beyond anything possible in modern laboratories.
Magnetic fields aren't nearly as important as a strong gravitational field. Small planets close to the sun (thus having a hot atmosphere) lose light molecules because their velocity exceeds the escape velocity of the planet. IIRC mars can just keep carbondioxide and oxygen, but not water, methane and lighter gases, but even CO2 and oxygen leak away slowly.
If you ever want to live on mars, a magnetic field may be convenient to keep fast charged particles from reaching the surface. They're great for causing mutations and other nasty things.
I mean, what is it with all of the different particles that these people seem to want to invent at every opportunity? Higgs bosons,technicolor particles, partons, selectrons, squarks, winos, zinos and dinos, they're all on the same scientific level as evolution - a piece of pseudo-science that cannot be proven by experiment. And as far as I knew, if it can't be proved by experiment, it isn't science at all.
A lot of these particles were actually "invented" to make theoretical physics agree with experiments. A good example is the neutrino: its existence was first postulated in the 1930s to account for the conservation of energy in beta-decay (without neutrinoes, a little energy was missing), and since then a lot of experiments have been done that confirm their presence. In the case of Higgs bosons, squarks and the like, these particles were postulated to keep theory in accordance with other experimental data (like particles having mass, and the existance of gravity). But having a theory that works doesn't automatically mean it's true, and that's why people like to observe these particles in an experiment. A confirmation of the theory would be nice, while proof that the theory is wrong would make people come up with a new theory that does agree with experiments.