The earth magnetic field is huge in size. That makes it protective although it's not very strong. A corresponding mag field of the size of a spacecraft would have to be very strong in order to deflect the high energy protons from the solar wind. If have to calculate it but it would probably of such strength that it would disturb the function of electric devices on the spacecraft.
I don't believe your 1 Angstrom RMS number, can you give a reference for that? Also the RMS roughness is not the critical number - it's the peak roughness, i.e. the largest bump of the surface, and I don't think that is is possible to push the peak roughness below a few Angstrom - remember an atom is about 1 Angstrom large - that would require atomically flat surfaces of several square centimeters.
You can judge the 3-dimensional form of things with one eye by moving your head or walking around it - which makes the discussed technology useful even for people that are blind on one eye.
You're intentionally trying to not understand. Just remember how the network for cellular phones works..and image how it would be if everyone would try to get a end-to-end connection in the old amateur radio or CB fashion: you'd need high power senders and a lot of bandwidth. The cellular networks work fine for a very high number of users, they only break down if you have too many users in one cell. Btw. their hubs do use directional antenna.
I forgot one point: 4) If you have moving parts they will release tiny particles when they move due to friction (and you have a lot of friction in vacuum), causing more problems. Keep in mind that there is no gravity forcing those particles down, so they would fly around and not necessarily adsorb on the surface to be wiped away.
1) It would destroy the optics. You would get scratches and the finish (anti-reflection coating and such) would also be scratched away. Basically you don't want any mechanical contact with optics.
2) There's no space for wipers when the condensate is somewhere within the lens system and you would need a seperate wiper for each surface.
3) The surfaces of optics are not flat but probably spheric or have some different form. It would be difficult to build a wiper for that geometry.
I think the biggest advantage of asteroid mining is: you don't have to lift the material out of earth's gravity well. Of course, to make this economically viable, you first need a demand for that material outside of earth.
...but really, what boon would we receive from a small, self-contained dome on Mars that needs resupply every so often from Earth? What could possibly justify the risks?
Well, what was the reason to leave Britain for America back then ? It was for political reasons! People went to America because they couldn't live in peace in the Old World. Many left for economical reasons (start a new life with free land). Of course many came to "get rich quick" a.k.a. Gold Rush but that wasn't really the basis of the society that developed in America. When I'm looking at the political climate today - at the anti-globalisation movement, at the freedom of information movement - I'm really beginning to think that sooner or later some people will be fed up enough with the circumstances here that they'll be willing to leave earth and start a new society, as far away as possible from the powers on earth.
for invisibility, what we need is a paint-on holographic display. anyway the proposed setup would not make completely invisible, but you would be very hard to spot.
I as a user hate flash sites because they take away power from me:
1) I can't use the BACK button to get back one step.
2) I can't search text with the browsers search function.
3) I can't resize the browser window to my comfort and have the content resized as well.
4) I have to learn how to use each and every site because everybody uses a different user interface (preferably using tiny fonts and tiny scrolling windows to display large amounts of text).
5) Murphy's Law: interesting sites always require the latest flash plugin, which unfortunately is not yet available for your platform.
6) Murphy's 2nd Law: if you have the required plugin version it will crash your browser.
Re:Why there will never be a time machine
on
Time Travel
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· Score: 1
I'd just like to note that the parallel universe idea replaces the irreversible flow of time with an irreversible fork off into a new instance of the universe. Apparently to keep the causality principle (a principle suggested by observation) a certain irreversiblity is necessary.
Re:ways around the time travel paradox
on
Time Travel
·
· Score: 1
Occams razor - good point. But how do you prove that your theory is simpler than the other ? I think you are mistaking "convenient" for "simple". Example: Newtonian mechanics looks simpler than Einstein General Relativity at the first glance, but in fact it's more complicated once you try to incorporate Electrodynamics. The experimental fact of a constant speed of light makes Newtonian mechanics mathematically more complicated than GR, however this was not obvious to Newton because he simply didn't know all the facts. For Newton, his theory was the simplest possible - if he suggested something along GR people would have called him "nuts" and accuse him of making the theory unnecessary complicated. Anyway: Mallett doesn't introduce a new theory, his concept of time travel keeps within GR. Last point: misunderstandings about paradoxa arise because the term "Time Travel" is not defined properly. As David pointed out above, it's not necessarily what you think it is.
I'll explain it to you: The crucial point is that all perceptions of you, what you look like etc. travel away from you at the speed of light (all interactions propagate with speed of light). Now, by travelling faster than lightspeed you are able to overtake the perceptions of you and you can see (perceive) what you did in the past. The faster and further you travel the further you travel back in time. In principle, if you travel instantaneously to a point 2000 lightyears away from earth, you could with a very good telescope look back to earth and witness Jesus walking around in the Middle East. Of course, this is not a "real" travel back in time as you cannot influence things that already happened, but you could definitely take a look at the past!
The above wording is imprecise. 9,192,631,770 Hz is the frequency of the electromagnetic wave that triggers a certain transition in a cesium-133 atom. So, what oscillates is not the complete atom, but the electric and magnetic field. Details can be found here
Anything powered by atomic energy is basically a steam engine
No, not necessarily. You can convert temperature differences directly in to electricity using the thermoelectric effect. Look up on Radio-Thermal-Generators (RTGs). The are used as energy sources for deep space missions (where solar cells would be impractical). You also don't need (and even don't want) to reach the critical mass! You don't want a chain reaction! You want slow release of the energy!
They didn't specifically say that they use a GeLi detector (they could also use high purity Ge).
One should mention that GeLi detectors need to be cooled all the time, even when not in operation, otherwise the Li distribution in the Ge crystal would be destroyed and the detector useless. This is not the case for high purity Ge detectors.
You are right about the chromatic abberations and how to avoid them using reflective optics. Another limit for collimating (or focusing) beams is the size of your light source: the larger the source the harder to achieve a good collimation/focus (in classical geometrical optics). Typically, flashlights have a quite large source (tungsten filament), so only part if it will be in the focus point of the parabolic reflector. OTOH, if your source is too small or you have small apertures (on the order of the wavelength) your beam divergence will be limited by diffraction.
Another issue with flashlights is that the light that directly goes towards the exit and does not hit the reflector will not be collimated and thus contribute to the divergence. Of course, flashlights are optimized for brightness, so you _have_ to use a reflector in order to gather the light that is emitted in the "wrong" direction. A lens would only collimate light that already goes towards the exit of the lamp.
They didn't specifically achieve (or try to achieve) mode-locking, but they mention the possibility (see below). They do not give a value for coherence length in the Nature article but there is a list of possible applications:
First, apart from supercontinuum generation, any other spectral configuration--for example, several contiguous bands with narrow gaps in between, spectral voids, or peaks in combination with continuous bands--could be designed. This might be of particular interest in custom-tailored light sources for spectroscopy or microscopy of inorganic, organic or biological specimens, including those with complex optical response functions. Second, by adding wavelength-selective optical feedback from an external grating, it might be possible to turn the supercontinuum laser described here into an ultra-widely (over several micrometres) wavelength-tunable source: such a source could be useful as a trace-gas sensor in atmospheric, environmental or medical applications. Third, by using a technique called mode-locking, a laser with a broad gain spectrum can be turned into a source of ultra-short pulses. By applying mode-locking to the laser we report here, we consider that it should be possible to obtain pulses as short as a few femtoseconds in the mid-infrared wavelength range. This would be an improvement by a factor of 1,000 over existing semiconductor sources, and opens up opportunities for time-resolved spectroscopy in the mid-infrared wavelength range. Last, if the design concept we report here could be applied to the fibre-optic or visible wavelength ranges, the resulting devices could be useful in optical data communications or for white light generation, respectively.
The single phase output of the laser effect has interesting optical properties.. but I don't believe it actually causes it to be any 'stronger'.
Actually, the phase locking of many different modes of a laser (=mode locking) is used to generate extremely powerful (>Terawatt) and short laser pulses. These pulses are a direct product of constructive interference of many different frequencies (inbetween the pulses you have destructive interference). Using mode-locking it is possible to generate from a 10 Watt continous wave laser a train of Terawatt peak power laser pulses (of course, average power is the same, or even lower).
looking at the Nature article, the "above threshold" spectrum goes from 6 to 8 um and looks almost rectangular, with some broad irregualr modulations and a maximum at 7.6 um. At higher spectral resolution one can see the individual Fabry-Perot modes (i.e. the individual modes of the resonator(s)).
The reason why Al metal (and every other metal too) is not transparent is the free electrons: they screen the electric field of light for frequencies below the metals' plasma frequency (which is high due to the high electron density). For Al the plasma frequency is in the far UV range at a wavelength of 15nm (visible light has 400..800nm), so radiation with wavelengths below 15nm is reflected (notice shiny appearance of metal surfaces). OTOH, you can make translucent metal coatings, if the metal film thickness is smaller than the wavelength to transmit.
Slashdot Mirror
Think about really big field-strengths. There still is Lorentz-Force, you'd have Hall-effects in many places.
The earth magnetic field is huge in size. That makes it protective although it's not very strong. A corresponding mag field of the size of a spacecraft would have to be very strong in order to deflect the high energy protons from the solar wind. If have to calculate it but it would probably of such strength that it would disturb the function of electric devices on the spacecraft.
I don't believe your 1 Angstrom RMS number, can you give a reference for that? Also the RMS roughness is not the critical number - it's the peak roughness, i.e. the largest bump of the surface, and I don't think that is is possible to push the peak roughness below a few Angstrom - remember an atom is about 1 Angstrom large - that would require atomically flat surfaces of several square centimeters.
The thermal vibration of atoms are much smaller than the atom itself. That wouldn't be a problem.
You can judge the 3-dimensional form of things with one eye by moving your head or walking around it - which makes the discussed technology useful even for people that are blind on one eye.
You're intentionally trying to not understand. Just remember how the network for cellular phones works..and image how it would be if everyone would try to get a end-to-end connection in the old amateur radio or CB fashion: you'd need high power senders and a lot of bandwidth. The cellular networks work fine for a very high number of users, they only break down if you have too many users in one cell. Btw. their hubs do use directional antenna.
I forgot one point:
4) If you have moving parts they will release tiny particles when they move due to friction (and you have a lot of friction in vacuum), causing more problems. Keep in mind that there is no gravity forcing those particles down, so they would fly around and not necessarily adsorb on the surface to be wiped away.
1) It would destroy the optics. You would get scratches and the finish (anti-reflection coating and such) would also be scratched away. Basically you don't want any mechanical contact with optics.
2) There's no space for wipers when the condensate is somewhere within the lens system and you would need a seperate wiper for each surface.
3) The surfaces of optics are not flat but probably spheric or have some different form. It would be difficult to build a wiper for that geometry.
I think the biggest advantage of asteroid mining is: you don't have to lift the material out of earth's gravity well.
Of course, to make this economically viable, you first need a demand for that material outside of earth.
...but really, what boon would we receive from a small, self-contained dome on Mars that needs resupply every so often from Earth? What could possibly justify the risks?
Well, what was the reason to leave Britain for America back then ? It was for political reasons! People went to America because they couldn't live in peace in the Old World. Many left for economical reasons (start a new life with free land). Of course many came to "get rich quick" a.k.a. Gold Rush but that wasn't really the basis of the society that developed in America.
When I'm looking at the political climate today - at the anti-globalisation movement, at the freedom of information movement - I'm really beginning to think that sooner or later some people will be fed up enough with the circumstances here that they'll be willing to leave earth and start a new society, as far away as possible from the powers on earth.
for invisibility, what we need is a paint-on holographic display.
anyway the proposed setup would not make completely invisible, but you would be very hard to spot.
I as a user hate flash sites because they take away power from me:
1) I can't use the BACK button to get back one step.
2) I can't search text with the browsers search function.
3) I can't resize the browser window to my comfort and have the content resized as well.
4) I have to learn how to use each and every site because everybody uses a different user interface (preferably using tiny fonts and tiny scrolling windows to display large amounts of text).
5) Murphy's Law: interesting sites always require the latest flash plugin, which unfortunately is not yet available for your platform.
6) Murphy's 2nd Law: if you have the required plugin version it will crash your browser.
I'd just like to note that the parallel universe idea replaces the irreversible flow of time with an irreversible fork off into a new instance of the universe. Apparently to keep the causality principle (a principle suggested by observation) a certain irreversiblity is necessary.
Occams razor - good point. But how do you prove that your theory is simpler than the other ? I think you are mistaking "convenient" for "simple". Example: Newtonian mechanics looks simpler than Einstein General Relativity at the first glance, but in fact it's more complicated once you try to incorporate Electrodynamics. The experimental fact of a constant speed of light makes Newtonian mechanics mathematically more complicated than GR, however this was not obvious to Newton because he simply didn't know all the facts. For Newton, his theory was the simplest possible - if he suggested something along GR people would have called him "nuts" and accuse him of making the theory unnecessary complicated.
Anyway: Mallett doesn't introduce a new theory, his concept of time travel keeps within GR.
Last point: misunderstandings about paradoxa arise because the term "Time Travel" is not defined properly. As David pointed out above, it's not necessarily what you think it is.
I'll explain it to you: The crucial point is that all perceptions of you, what you look like etc. travel away from you at the speed of light (all interactions propagate with speed of light). Now, by travelling faster than lightspeed you are able to overtake the perceptions of you and you can see (perceive) what you did in the past. The faster and further you travel the further you travel back in time. In principle, if you travel instantaneously to a point 2000 lightyears away from earth, you could with a very good telescope look back to earth and witness Jesus walking around in the Middle East. Of course, this is not a "real" travel back in time as you cannot influence things that already happened, but you could definitely take a look at the past!
Hmm, very insightful comment. One question: what is so special about submanifolds of half the dimension of the manifold ?
The above wording is imprecise. 9,192,631,770 Hz is the frequency of the electromagnetic wave that triggers a certain transition in a cesium-133 atom. So, what oscillates is not the complete atom, but the electric and magnetic field. Details can be found here
Anything powered by atomic energy is basically a steam engine
No, not necessarily. You can convert temperature differences directly in to electricity using the thermoelectric effect. Look up on Radio-Thermal-Generators (RTGs). The are used as energy sources for deep space missions (where solar cells would be impractical). You also don't need (and even don't want) to reach the critical mass! You don't want a chain reaction! You want slow release of the energy!
They didn't specifically say that they use a GeLi detector (they could also use high purity Ge).
One should mention that GeLi detectors need to be cooled all the time, even when not in operation, otherwise the Li distribution in the Ge crystal would be destroyed and the detector useless. This is not the case for high purity Ge detectors.
You are right about the chromatic abberations and how to avoid them using reflective optics. Another limit for collimating (or focusing) beams is the size of your light source: the larger the source the harder to achieve a good collimation/focus (in classical geometrical optics). Typically, flashlights have a quite large source (tungsten filament), so only part if it will be in the focus point of the parabolic reflector.
OTOH, if your source is too small or you have small apertures (on the order of the wavelength) your beam divergence will be limited by diffraction.
Another issue with flashlights is that the light that directly goes towards the exit and does not hit the reflector will not be collimated and thus contribute to the divergence. Of course, flashlights are optimized for brightness, so you _have_ to use a reflector in order to gather the light that is emitted in the "wrong" direction. A lens would only collimate light that already goes towards the exit of the lamp.
The single phase output of the laser effect has interesting optical properties.. but I don't believe it actually causes it to be any 'stronger'.
Actually, the phase locking of many different modes of a laser (=mode locking) is used to generate extremely powerful (>Terawatt) and short laser pulses. These pulses are a direct product of constructive interference of many different frequencies (inbetween the pulses you have destructive interference). Using mode-locking it is possible to generate from a 10 Watt continous wave laser a train of Terawatt peak power laser pulses (of course, average power is the same, or even lower).
looking at the Nature article, the "above threshold" spectrum goes from 6 to 8 um and looks almost rectangular, with some broad irregualr modulations and a maximum at 7.6 um. At higher spectral resolution one can see the individual Fabry-Perot modes (i.e. the individual modes of the resonator(s)).
The reason why Al metal (and every other metal too) is not transparent is the free electrons: they screen the electric field of light for frequencies below the metals' plasma frequency (which is high due to the high electron density). For Al the plasma frequency is in the far UV range at a wavelength of 15nm (visible light has 400..800nm), so radiation with wavelengths below 15nm is reflected (notice shiny appearance of metal surfaces).
OTOH, you can make translucent metal coatings, if the metal film thickness is smaller than the wavelength to transmit.
oops, you are both right...I'm way off, mixed up the exponents. 1 millisecond is really (really) long.