Solar Sail Will Work, says Planetary Society 290
degauss writes "In response to Cornell Physicist Thomas Gold's paper declaring the theroy behind solar sails flawed (previously mentioned in this Slashdot article), Louis Freedman, executive director of the Planetary Society (the organization behind the COSMOS project), has written a brief rebuttal to the claims in Dr. Gold's paper regarding the feasibility of solar sails for use as a method of transportation in space. He does not go in to detail with equations and such, but does give an overview of the reasons he believes Gold's hypothesis is incorrect."
Briefer rebuttal (Score:2, Funny)
"It's gonna work!" (Score:5, Funny)
"Check this out! - It's gonna work!"
Re:"It's gonna work!" (Score:2)
duh, simple... (Score:2, Insightful)
There is a simple, yet somewhat expencive, way to see who's right.
Built a satelite / spaceprobe with a whopping huge and light (mylar maybe?) sail. Launch into space (as the sail will be then main experiment on this one, it can be relatively light and might piggyback anotehr launch). Deploy sail. Wait and see what happens. THEN one can sit down ans find out if current theories are on the mark.
Re:duh, simple... (Score:3, Informative)
What, like this one [planetary.org]?
Read the artical first next time mate.
-Alex
Re:duh, simple... (Score:2)
I did in fact read the article first. The entire point of my post was that instead of arguing beforehand if it'll work, they ought to build it and then see if the current theories do infact hold water.
lets review the scientific method (Score:5, Informative)
1. Observation and description of a phenomenon or group of phenomena. - In this case, all sorts of different light experiments
2. Formulation of an hypothesis to explain the phenomena. In physics, the hypothesis often takes the form of a causal mechanism or a mathematical relation. - In this case, Maxwell's theory, and then the Quantum Mechanical changes it suffered
3. Use of the hypothesis to predict the existence of other phenomena, or to predict quantitatively the results of new observations. - In this case, there are 2 predictions in consideration: Solar Sails work because of [read the article for info], Solar Sails don't work because of [read the older article for info].
4. Performance of experimental tests of the predictions by several independent experimenters and properly performed experiments. - In this case, build it and try it.
You are suppose to argue beforehand,that is step 3. That is the way you really understand your theory and its implications. The arguing beforehand is a very important step to clarify what someone is really saying with his/her theory. After observing a phenomena it is very easy to come up with hundreds of explainaitions, but the only good ones are the ones that predict new stuff, and clarifying the theory allows us to make more precise experiments that really show light into the important issues. Arguing the different theories is what makes them more specific that just betting for the outcome of an experiment.
I think you forgot a step (Score:4, Funny)
you are right, i forgot some steps... (Score:3, Funny)
2. Formulation of an hypothesis to explain the phenomena.
3. Use of the hypothesis to predict the existence of other phenomena.
4. Apply for a scientific grant and have some graduate students to get a lil' profit
5. Perform experimental test.
6. Apply for a patent. You will get the patent, is too easy these days.
7. Sue someone and profit even more
capitalism, not socialism here, buddy. (Score:3, Insightful)
What bothers me here is that are trying to drum up karma by catering to the USPTO sucks, and lawsuits suck
Solar sail technology is legitimately patentable even though it is gritting on the nerves of those who have not made a considerable investment in the development of anything ever.
Readers and contributers to this site seriously need to learn that it ta
Re:duh, simple... (Score:5, Interesting)
The interesting thing is that the Mercury orbiter that NASA launched (one of the pioneer series) used the pressure of sunlight on its solar panels, just like a solar sail would on the sail material, to give it a spin. That, IMO, gives the theory supporting solar sails working a whole lot more credibility.
Re: (Score:3, Informative)
Re:duh, simple... (Score:2)
You're right. It wasn't an orbiter. It flew by a handful of times. NASA is working on a new Mercury Orbiter though. IIRC, through the Discovery Program and called Messenger [spaceref.com].
I'll keep looking for a reference on the solar panel bit.
Re:duh, simple... (Score:2)
I should have waiting 30 seconds more on that last post. Check here [google.com]. Check the whole thread. That's Geoffery Landis again. The best of the bunch looks like Henry Spencer's answer [google.com] (Yes *THAT* Henry Spencer).
Re:duh, simple... (Score:2)
I think what is theorised here is an extremely light (read: thin) sail, which must be made as cose to 100% reflective as possible in order to avoid burning up with absorbed solar energy.
This is what is being disputed; whether or not an object that reflects nearly 100% of the photons can have momentum imposed on it by those same photons.
Re:duh, simple... (Score:2)
Re:duh, simple... (Score:2)
Solar Sails may work but not practical (Score:2, Interesting)
The acceleration to get to 100 mph is what ?
100 years ?
Re:Solar Sails may work but not practical (Score:3, Insightful)
Re:Solar Sails may work but not practical (Score:2)
Re:Solar Sails may work but not practical (Score:4, Informative)
Re:Solar Sails may work but not practical (Score:2)
http://www.geophys.washington.edu/Space/SpaceMo
You may also call it a solar sail
Re:Solar Sails may work but not practical (Score:3, Insightful)
1400 W/m2. The sail on the COSMOS spacecraft is about 1km2 and the total weight of the thing is about 1kg.
The force works out to be about 9N, and so the accelaration to 9m/s2. This is slightly less than the acceleration due to gravity.
If you jump off a bridge you should find that you accelerate to 100mph quite quickly.
Re:Solar Sails may work but not practical (Score:2)
It's not 9.8m/s2 elsewhere, you know...
Re:Solar Sails may work but not practical (Score:2)
8E-3 newtons, which would accelerate a kilogram a bit less than a milligee.
At the end of a day you'd have gained 700 meters per second. At the end of a month, 22 kilometers per second, and you've long since escaped from Earth orbit.
Sure, it's all well and good *now*... (Score:4, Interesting)
The main practical difficulty I see is stopping. You can't slap propelled rockets on the ship to do the job; if you did, I would want to know you didn't propell you ship with that to begin with.
Maybe some fancy gravity trickery... deaccelerate as a star's gravity starts to whip you around. Other than that, I don't see how you could do it. I still don't see a use for these other than minute corrections in satellite trajectories. They're not directional, and the methods by which, say, sailboats can sail against the wind won't work here. Only way to slow yourself down is to stop sailing and let gravity do it's thing... a big problem when you're somewhere in space in which gravity isn't acting against you. Moreover, we wouldn't get very far away, because the force provided by sunlight diminishes exponentially as you move further away. And going towards another star wouldn't help, because you can't sail against the "wind" in this case (ship sails can because of how the wind will curve and press on the sail in a different direction than what it was originally travelling, which won't happen with light).
We're getting to the point where it will just take too long to go where we want to go, and eventually it's going to make us ask if we really can go there. I mean, hundreds of years later, who's going to care that a probe, unable to communicate with us, is careening somewhere past Neptune? As for people, don't hold your breath on this transporting us; it just takes too long. I don't know about you, but going to another planet wouldn't be worth most of my life, if not the whole thing and part of my children's. And I don't even want to hear this whole "Once we figure out how to go faster than light" garbage. You've all been taking Star Trek too seriously. Granted, people didn't believe we could fly, or the earth was round, blah blah blah. As we progress we do realize that things were wrong, but some things become more compellingly right as well. The speed of light, the fact that we can't exceed it and its correlation with time are what defines our reality. Sending something faster than light, AND slowing it back down without the obvious logical and physical laws getting in the way is impossible. Sending something as complicated and sensetive as an organism is absurd. Sending an organism as intricate as a person should be grounds for insanity.
Sorry, that just bothers me when geeks worldwide sit back after watching something on the Sci-Fi channel and think "Man, once we learn to warp... that'll be good times my friend", to which his friend replies "Affirmative" and starts taking readings on his platic light-up box... er, tricorder.
It's always the turtle that wins...
Unless there's a dog running after you. I got 5 bucks on the hare.
Re:Sure, it's all well and good *now*... (Score:4, Insightful)
Presumably you'd want to travel to another solar system. In that you'd set the sail in the other direction as you get closer.
Moreover, we wouldn't get very far away, because the force provided by sunlight diminishes exponentially as you move further away.
Rubbish. You are accelerating the whole time it takes you to leave the solar system. Just because you stop accelerating after that doesn't mean you stop. And the force acting on the sail drops off as 1/d*d which is polynomial, not exponential.
And going towards another star wouldn't help, because you can't sail against the "wind" in this case
You could collapse the sail.
We're getting to the point where it will just take too long to go where we want to go, and eventually it's going to make us ask if we really can go there. I mean, hundreds of years later, who's going to care that a probe, unable to communicate with us, is careening somewhere past Neptune? As for people, don't hold your breath on this transporting us; it just takes too long. I don't know about you, but going to another planet wouldn't be worth most of my life, if not the whole thing and part of my children's.
Not everyone is like you. (the kind of person who would sit back and say "impossible, the earth is flat" as Columbus sets sail.) I am kind of proud to think that the two Voyagers (both of which are still sending data) are out past Neptune. And the physicists who study the heliopause and the inter-stellar medium still find their data useful.
Re:Sure, it's all well and good *now*... (Score:2)
You could collapse the sail.
Which would only slow you down if the largest source of gravity were behind you, which isn't the case if you're going towards another star. You would have to reverse the sail around half-way through, making this whole ordeal take even longer.
two Voyagers (both of which are still sending data) are out past Neptune.
Yep, with conventional rockets and slingshot maneuvers a
Re:Sure, it's all well and good *now*... (Score:2)
Re:Sure, it's all well and good *now*... (Score:2)
Re:Sure, it's all well and good *now*... (Score:2)
And where would this be, exactly? Where there's no gravity?
All a solar sail does is to change orbits, by speeding up or slowing down. But changing the orbit of an object in earth orbit to a Mars orbit might conceivably be a very useful thing to do. Next time, before theorizing, read the FAQ [planetary.org].
Re:Sure, it's all well and good *now*... (Score:2)
Well, it was widely believed to be impossible. When there is no friction you can always invert the trip - in other words if such trickery were possible it could be used to accelerate you in the first place.
Actually you can do a little bit of this in three body systems (e.g., sun, planet, craft); perhaps you have heard of sling-shot manouvers. But again, they
Re:Sure, it's all well and good *now*... (Score:2)
As has been noted, if you're going to another solar system, you use that sun's push to slow you down.
Another way is to have a big chunk of the sail detach and reflect light back at a smaller chunk of sail you hold onto. The big chunk accelerates away faster, but the light it focuses back on the smaller chunk slows you down.
Of course, if you build a big enough laser, you can have light just about anywhere you need it. You can have as powerful an engine as
Ways to stop (Score:3, Interesting)
1. Angle the sail to oppose your orbital motion. In the extreme case, stop relative to the sun and fall inward.
2. Carry the rockets. At least you won't be incurring the cost of rockets to push the braking rockets out to where they're needed.
3. Aerobrake, as one of the sibling replies suggested.
4. Send a dispo
Re:Sure, it's all well and good *now*... (Score:2)
Differential thrust for propulsion (Score:2, Interesting)
Re:Differential thrust for propulsion (Score:3, Informative)
Re:Clarification to question (Score:2)
A couple of questions come up however.
1)Is the material that works well for differential thrust, (preferably a material that will cause nearby mollecules to warm up, and bounce off of the surface) function well as a solar sail? My suspicion is that it does not, as I believe that a solar sail is going to function best as a means of ch
Re:Clarification to question (Score:2)
-Rusty
Re:Clarification to question (Score:2)
Oddly enough... (Score:3, Funny)
Well of course. This was utter nonsense. (Score:5, Informative)
But what will be the performance of the mirror as a heat engine? If the mirror receives heat energy from the Sun and converts some of this into free energy, namely the kinetic energy of its motion, it falls into the strict definition of a heat engine, and Carnot's rule defining the maximum efficiency for this energy conversion must apply. We can determine the incoming temperature of the radiation by measuring the temperature an absorbing (black) body would reach when exposed to the radiation being sent to the mirror, and the temperature a black body would reach exposed to the outgoing radiation from the mirror, both measurements carried out in common motion with the mirror. Carnot's rule would then give the maximum efficiency as that fraction of the heat flow trough the mirror, given by the difference of the two temperatures, divided by the input temperature. It would be that fraction of the heat flow that could maximally appear as kinetic energy gained by the mass of the mirror. If this was a perfect mirror, the two temperatures will be the same, and it follows that the mirror cannot act as a heat engine at all: no free energy can be obtained from the light. The proposed solar sail cannot be accelerated by sunlight.
The two temperatures are NOT the same. They are slightly different. The mirror is not infinitely massive, so in the mirror's own reference frame the photons reflecting from the mirror have a lower energy / longer wavelength after their elastic collision with it- the mirror receives a small bit of momentum from each photon in the collision. And in the sun's frame, the mirror is receding and the reflected photons are doppler shifted. He can't assume that the incident and reflected energy are the same and run off making derivations from that. They are extremely close, but the difference between them is not zero like he assumes.
Would it be better to place a black sheet there instead of a mirror-faced one? Unlike the mirror, this could absorb energy and the momentum associated with that. But it would do this only from the moment of its exposure until it reached thermal equilibrium with the available radiation. Then energy absorption would cease, and with that the delivery of momentum to the sheet would also cease. For any lightweight sheet, this time would be only seconds.
Does he even realize the sun is a point source? The sun shines on one side of the sail, not both sides! One side is exposed to radiation with a temperature of 300K. The other side sees only 3K radiation. The sail temperature will rise to some intermediate temperature between 3 and 300K and reach thermal equilibrium with all available radiation. So what? This means nothing for momentum transfer! Once it reaches thermal equilibrium, the sail is receiving X watts of radiation coming from one direction, and radiating X watts thermally in all directions! While the wattages are the same for both, the radiated energy has no overall momentum, while the incoming energy has a very definite momentum. The point isn't to heat the sail, it's to move it. He seems to be confusing the sail's kinetic energy of motion with its internal thermal energy.
The rebuttal is very sparing. I think it would probably have been more vicious if its author didn't "know Prof. Gold well" and didn't have any reservations about embarrassing him.
Re:Well of course. This was utter nonsense. (Score:5, Informative)
This is true, but not the reason why the Carnot analogy fails.
The main point is that the mirror is not receiving "heat energy" (a scalar quantity), but a constant radiation directed radiation pressure ( I hate the term "pressure", because pressure to me seems to be a local scalar quantity but such is jargon.), a directed constant force (i.e. a vector quantity.) So the MIrror is NOT a heat engine. A battle analogy is that the Sun is the engine powering the "mirror".
The sail temperature will rise to some intermediate temperature between 3 and 300K and reach thermal equilibrium with all available radiation.
Not 300k. The Sun is approximately a Blackbody at 6000k, so the mirror sees a Planck spectrum of radiation at 6000k in one side, and cosmic microwave 3K on the other. THe rest your explanation is spot on.
Re:Well of course. This was utter nonsense. (Score:2)
terms is helpful. There is no reason why we
shouldn't be able to balance out energy as a
scalar quantity. In fact writing a Hamiltonian
for the sail is not that hard and Dr. Gold would
then easily see his fallacy by solving it.
Re:Well of course. This was utter nonsense. (Score:5, Informative)
Re:Well of course. This was utter nonsense. (Score:2)
I was referring to the equilibrium temperature of a blackbody in that position, which meets the requirement that its radiating surfaces are all at the same temperature. This is almost true for the earth because of the atmosphere, and by a solar sail because it is so thin. (It was just for sake of argument, to demonstrate that the radiated energy may in general have zero overall momentum in the mirror frame. This isn't a real requirement.)
Re:Well of course. This was utter nonsense. (Score:2, Interesting)
The "equilibrium temperature" of any object in space, where the only dominant source of heat transfer is radiation, depends completely on the thermal surfaces of this object.
Earth's "equilibrium" temperature is about 300k, that's true. But for other spacecraft, its equilibrium tempreature depends on what kind of thermal surfaces the engineer stick on it. Most spacecraft aims for 300k, since the spacecraft's instruments are from Earth, and most "normal" components have their optimum operating temperatur
Re:Well of course. This was utter nonsense. (Score:2)
You've got to love physicists, saying things like that, as if they are actually true. ;)
Re:6000K is wrong (but 300K is too low) (Score:2)
It depends on the body and its emissivity properties. To be in equilibrium with the Sun, a body must emit as much flux as it is receiving from that sun. FOr an object near EArth's orbit with the Sun, it is 1.4kW/m^2. Earth's emissitivity ensures that its effective temperature is about 300k ( i.e. Flux = stefan-boltzman constant * T_eff^4). Remember the Blackbody temperature is only a definition,
Re:Well of course. This was utter nonsense. (Score:3, Informative)
No it wouldn't be better. If the photon is reflected then the solar sail craft gains twice as much momentum as it would if the photon is absorbed.
Tiny redshift == impractically slow acceleration? (Score:2)
This point was raised in the previous
Re:Tiny redshift == impractically slow acceleratio (Score:2)
The point is that the interaction between the sail and the photons is characteristic of an elastic collision, exchanging momentum, with an associated increase in entropy. It's a trivial and easily understood interaction. There's just no hole here that you can poke a thermodynamic argument into. If some guy wants to convince us that this is a "heat engine" and then derive the fact that it can't wor
Re:Tiny redshift == impractically slow acceleratio (Score:2)
If this is an elastic collision, and the sail gains energy, then the photon must lose some energy. Where do you propose this energy comes from? Clearly, the photon's velocity can'
Re:Tiny redshift == impractically slow acceleratio (Score:2)
The photon's initial energy.
Clearly, the photon's velocity can't decrease. Hence the redshift.
That's the redshift from the elastic collision, not the redshift from the mirror's motion relative to the solar system. They are two different redshifts.
Not true. I'm sure you would not say this had the argument been based on conservation of momemtum, or conservation
Re:Tiny redshift == impractically slow acceleratio (Score:2)
Yes, but the point is that they're not the same energy, because the sail has a finite mass. They will have a slightly redder color for having scattered off it. So the kinetic energy of the mirror can change and there is no problem.
A mirror moving away from the s
And of course, the simplest rebuttal to Gold (Score:3, Insightful)
Wehrner Von Braun said it best (Score:5, Insightful)
That Gold Guy (Score:3, Offtopic)
And he's got the biggest feature of the crank, a martyr complex:
(That's from a journal article [amasci.com] he wrote.) Now from a purely scientific point of view, one is inclined to accept that Gold was the victim of medical close mindedness. The notion of "active hearing" does make a lot of sense, and medicos are notoriously rigid with respect to scientific issues. But other physical scientists have managed to bridge this gap: Norbert Weiner comes to mind. In fact, the very theories that Gold was trying to apply to hearing were originated by just that kind of cross-discipline collaboration.I have to suspect that Gold likes to play the contrarian just to avoid dealling with his on collaboration issues.
Useful explanatory link (Score:5, Informative)
A Rebuttal [google.com] by Geoffery Landis [sff.net].
Geek Fight! (Score:3, Funny)
(Or is it their compasses? [compassi?] {I mean the pointy ones with the stabbing..and he eyes....glavin!})
of course he's wrong (Score:3, Informative)
Re:of course he's wrong (Score:2)
career opportunities (Score:5, Funny)
My career as a Solar Pirate is looking more promising everyday
Yarrr!
ILLEGAL (Score:3, Funny)
Interesting... (Score:3, Interesting)
When the photons are travelling towards the sail an observer at the light source will see a red shift (doppler effect at work here).
When the photons are travelling away from the sail an observer at the light source will see a blue shift.
Because the observer hasn't changed position the shift can be attributed to a change in energy, which must have gone into the sail (as the only thing the photons encountered, assuming a perfect vaccume) meaning that the increased KE of the sail breaks no laws of physics.
Re:Interesting... (Score:2)
With all due respect to Doctor Gold (Score:4, Informative)
Applying the laws of thermodynamics that govern a heat engine to a sail is just not applicable. You might as well apply Kirchoffs current law to a water balloon.
This is a straight forward conservation of momentum problem. Give a sail of size A, with reflectivity R and a photon flux F(photons/sec) impinging on the sail with average frequency f you will have have momentum imparted to the sail of M=2*(F*R*h*f)+(1-r)*h*f. h is plancks constant. QED and very straightforward.
Well I was dissapointed by pons and fleischman, Golds theory about the inorganic, I now see how and why you can have otherwise respectable people make completely foolish statements
Re:With all due respect to Doctor Gold (Score:2)
Professor Simon Newcomb (Score:5, Interesting)
"Flight by machines heavier than air," Simon Newcomb declared one day in 1902, "is unpractical and insignificant, if not utterly impossible."
His arguments were quite reasonable on the surface - Imagine a bird as a model. If you increase the size of the bird, the mass increases proportionally to the third power of its wingspan. But the surface area of the wings only increases proportionally to the square of its wingspan. Thus something much larger than a bird would never be able to fly, and all attempts to build heavier than air flying machines capable of carrying a human would prove futile.
Fortunately, the Wright brothers never read his paper, or at least never took him seriously.
About 40 years later it was argued by learned men that manned supersonic flight would never be achievable.
http://www.garfield.library.upenn.edu/essays/v3
Marconi wasn't formally educated, and he was laughed at for spending vast sums of money to send a radio signal across the Atlantic ocean. Any fool knows that radio waves couldn't penetrate the earth, and was limited to line of sight communication! Yet despite all logic, the damned fool contraption eventually worked. It was only later that they discovered the ionosphere could reflect certain frequencies back to earth.
Even great men of science make mistakes sometimes.
Re:Professor Simon Newcomb (Score:2)
Sure, they laughed at Marconi and his "crazy" ideas, but they also laughed at Bozo the clown. Sometimes an idiot is simply an idiot.
Newcomb did better than Gold (Score:2)
Newcomb did't foresee lightweight power plants with output in the tens or hundreds of horsepower.
In other words, at least Newcomb got the physics right.
Temperature of Photons?? (Score:2)
If I'm right with my thermodynamics knowledge, the temperature of the photons would be their *unordered* move (that is, relative to their mass centre). And this is nearly zero.
speaking of solar sails (Score:2)
Sci-fi fans (or naval adventure fans, or people who like good books) who dig this whole solar sail business are highly encouraged to check out Michael Flynn's recent book The Wreck of the River of Stars. Hardcore space adventure aboard the last of the great solar sail ships, put out of business by fusion technology. It's a romantic yet compelling look at space-travelin' technology. Flynn's a talented writer, the type who can name his chef Eaton Grubb and get away with it. Good summer read. [amazon.com]
Heh heh. Of
My note to New Scientist (Score:5, Informative)
Tommy Gold and others quoted in the article about solar sails really should consult some real spacecraft engineers. For us, solar radiation pressure is an everyday reality. Solar radiation pressure is a major perturbing force on GPS satellite orbits, for example.
AMSAT, a group of radio hams that builds its own satellites, has for decades used radiation pressure to impart slow spins to its satellites with "blade turnstile" antennas. Paint one side of each blade black and the other white, and the spacecraft slowly spins like a Crooke radiometer -- but in the opposite direction, away from the white surface.
A Crooke radiometer is a very different beast. The glass bulb is not evactuated, so thermal heating on the black side of the vanes heats and expands air, pushing the vane away from the black surface. This force overwhelms the much smaller photon pressure, but in the vacuum of space only the radiation pressure exists.
Gold's thermodynamic argument is silly and wrong. A solar sail is not a heat engine, so the second law doesn't apply. The first law (energy conservation) does apply in a very simple way: the photons reflecting off the sail are red-shifted by the sail's motion, removing energy from the photons and imparting it to the sail by accelerating it.
Momentum transfer (Score:3, Informative)
1) Light impinging on the sail and reflecting back towards the sun. The photons have momentum due to relativity.
2) Photons being absorbed by the sail (increasing its temperature and transferring momentum to the sail)
2) Photons being radiated in all directions by the sail (radiant heat).
Conservation of momentum shows that the sail has to accellerate, but he's right that it will start out increasing rapidly, and as it heats up it will slow down its accelleration (because it starts to radiate infra-red on the side away from the sun)
I think this is the sense in which it is a heat engine.
The conservation of energy and the fact that the sail accellerates away from the sun does imply red shifts of the reflected photons (ie. reduction in their energy). This doesn't seem to bother me at all. It seems to be what bothers Gold.
What about Echo-1 and -2? (Score:3, Informative)
http://www.centennialofflight.gov/essay/Diction
Improving on the idea of sending and receiving
signals from the moon, in 1960, NASA launched a
balloon satellite that would reflect communications
signals. Echo I was a balloon made of
aluminum-coated Mylar that was launched by a
rocket into space. When it reached orbit 1,000
miles (1,609 kilometers) above the Earth, it
inflated from inside a 26.5-inch (67.3-centimeter)
magnesium sphere to 100 feet (30.48 meters) in
diameter. Circling the globe every two hours, it
shone more brightly than the North Star in the
evening. The balloon captured the imagination of
people who had watched the first man-made object
in space, the Russian satellite Sputnik 1, orbit the Earth in 1957.
Umm? (Score:3, Informative)
To sum up... (Score:4, Informative)
1) Photons bouncing off a mirror will impart momentum to the mirror. That's Newton's laws right there, as fundamentally a part of the fabric of the nature of reality as we know it as damned near anything else we have ever studied. If Gold were right and a Solar Sail wouldn't work, then it would mean Newton's 3rd law would be violated, and that's super bad mojo, mojo of a scale that Gold was unable to back up with sufficient evidence and argumentation in his penny-ante paper.
2) The laws of thermodynamics are not violated by the operation of Solar Sails. In any given inertial reference frame the reflected photons will be "red shifted" and have a slightly lower energy. This is how energy is conserved (since the movement of the sail represents work, and thus energy). This is also how the 2nd law of thermodynamics (non-decreasing entropy) is followed, since the redshifted photons are higher in entropy (for slightly complicated reasons) and balance the work done.
3) Light pressure is not theoretical, it has been detected, measured, and, indeed, used many times in many circumstances. Its properties have corresponded very closely (to about as many 9s as you'd like) to what has been theorized.
In short, Gold is full of crap and the New Scientist ought to be ashamed at printing his stupidity.
Gold is a crackpot, but Freedman's rebuttal is bad (Score:3, Insightful)
Freedman's rebuttal says that Gold is wrong to argue from a thermodynamic point of view, and that he ignores quantum mechanics. However, all the laws of physics must be consistent with each other. This consistency is what makes these intellectual arguments so interesting. For example, by insisting that electrodynamics was consistent with mechanics, Einstein developed special relativity.
Gold's arguments are simply wrong, but this incorrect rebuttal is not really that good. When debating with crackpots, it's important to be meticulous in your arguments, because they will seize upon any small error and attempt to make that the focus of the debate, not their own large, glaring errors.
Re:can solar sails over come the sun's gravity? (Score:3, Informative)
Any object that orbits another body is using centrifugal force (pushing it away from the center) to ballance the gravitational force (pulling it toward the center). By giving any object a small push faster around in its orbit you increase its centrifugal and cause the object to move to out to a farther orbit.
So yes, adding solar sails to a NEO would help
Re:can solar sails over come the sun's gravity? (Score:3, Informative)
Momentum wants to keep the earth going in a straight line out into deep space.(tangent to the orbit we are currently in) Gravity pulls us away from that line. Closer to the sun. The spot closer to the sun happens to be right on the orbit line. Repeat.
Re:can solar sails over come the sun's gravity? (Score:5, Funny)
If you want to get pedantic about it, there's no such thing as gravity. It's just inertia/momentum acting on a curved space-time.
(at least if you buy general relativity)
Re:can solar sails over come the sun's gravity? (Score:2)
Similarly: 0.01G over a year would give you roughly 2000miles/second acceleration -- fast enough, I think to start getting obvious relativistic side-effects. (and, man, you do not want to hit a rock at those speeds!)
Stopping a fastball with a kleenex (Score:2)
Re:Yeah, BUT.... (Score:2, Informative)
we carry a harpoon! (Score:2)
Wow the troll returns! (Score:2)
Clever dick, keep it up. You're an impressive fool.
Should be VladTheFag.
Re:Another indicator (Score:5, Insightful)
Depends on when he did this "seminal work on the steady-state theory". I'm in my 40s, and I remember when it was still considered acceptable to have some reasonable doubt about the big bang. If he's in his 70s, and did this work, say, 50 years ago, it's possible that the work was considered completely solid at the time. And the word "seminal" does imply that it was a while back.
I'm reminded of Stephen J. Gould's defense of the Bishop of Usher (the one who determined that the universe was created in 4004BC). Looking at that date based on what we know now, it's easy to assume that he was a religious fanatic, but if you look at what was known at the time he did the work, it turns out that he actually did some pretty solid scientific research to come up with that date. The fact that he was working from a set of bad assumptions was not really his fault.
So, back to Gold, if he's still a proponent of the steady-state, then he can probably be dismissed as a quack, but the fact that he once worked on the theory doesn't really say anything one way or the other.
Re:Another indicator (Score:2)
An alternative theory to the Big Bang was proposed in 1948 by Hermann Bondi, Thomas Gold, and Sir Fred Hoyle It was called the steady-state theory. They found the idea of a sudden beginning to the universe philosophically unsatisfactory.
Daniel
Re:Another indicator (Score:2, Insightful)
The actual theoretical work done in exploring the logical space of any theory, accepted or idiotic, can have a value entirely independent of the value of the theory itself. I am not familiar with Dr. Gold's work, but I would not
I think Barbara Gamow said it best: (Score:2, Funny)
"Your years of toil,"
Said Ryle to Hoyle,
"Are wasted years, believe me.
The steady state
Is out of date
Unless my eyes deceive me,
My telescope
Has dashed your hope;
Your tenets are refuted
Let me be terse
Our Universe
Grows daily more diluted!"
Said Hoyle, "You quote
Lemaître, I note,
And Gamow. Well forget them!
That errant gang
And their Big Bang-
Why aid them and abet them?
You see, my friend,
It has no end
And there was no beginning,
As Bondi, Gold
And I will hold
Until our hair is thinning!"
personal attack (Score:4, Informative)
Here are two cases
(a) Another BIG proponent of the Steady State universe is Fred Hoyle.(While we are at it, let's throw in that Hoyle also supported life from space rocks theory). Is he a quack? No. He has good arguments. In fact, Fred Hoyle is sadly forgotten for his VERY seminal work on figuring out how the Sun nuclear engine works. Sadly the Nobel committee only awarded Willie Fowler the Nobel though Hoyle arguably did as much to solve the problem : an scandalous injustice that many astrophysicists now rued.
(b) You can also attack Friedman's comment about the "obscure british "preprint physics archives".
A number of colleagues have contacted me since the web posting (on a rather obscure British web site of "e-print physics archives", http://uk.arXiv.org.)
The arXiv is the main distribution of physics and maths papers nowadays. Everybody in the field reads the archives. In fact the uk.arXiv.org is just one of the many mirrors of the main site arXiv.org [arxiv.org] hosted, ironically by Cornell.
So Friedmann did a "personal attack" on Gold (implying that Gold only published his findings in some no-name website). THat's not a good thing. A good scientist names his source without judgement : the reader can decide for himself whetehre it is good or not by its contents.
Re:personal attack (Score:4, Insightful)
I'm sorry, but no. I've not read Gold's work or even heard of him, but I read a number of Hoyle's papers. In the early 1950s, steady state was a perfectly respectable theory with a few minor bumps from observations (such as the Hubble expansion). In the subsequent 50 years, the observations have gotten much more rigorous, much more extensive, and much more valid. They have also become much, much, much more difficult to explain via steady state. Fred Hoyle -- admittedly once a great astronomer -- has become increasingly shrill and outlandish in his theoretical constructs designed to explain the "illusion" of the cosmic background radiation.
You're entirely right that the merits of a scientific position ought not be dismissed due to the personalities of the people who hold it. But equally true is the statement that no scientific position ought to be elevated merely because some proponents once did good work, in a different subdiscipline.
Re:personal attack (Score:2)
This guy's an engineer though. He probably cares less about the cult of scientism than he does about making his invention work.
"The scientist describes what is, the engineer creates what never was"
Re:personal attack (Score:2)
We have a mathematician, physicist and an engineer. A fire erupts in the house.
The physicist walking in to the room, sees the fire, does some calculations, gets a bucket of water and dumps it on the fire. With the last drop of water the fire goes out.
The engineer walking in to the room, looks at the fire, grabs the biggest possible bucket, fills it full of water and dumps it on the fire, soaking the entire room, ruining furniture and electronics.
The mathematic
Re:personal attack (Score:2)
Re:Another indicator (Score:3, Insightful)
Though no idea should be dismissed a priori in science, this alone calls into question Dr. Gold's ability. Unless they're using "steady state" in a manner unconnected to its traditional usage, Dr. Gold is on the side of a theory that has pretty much fallen by the wayside. Excluding the increasingly, um, eccentric Fred Hoyle, there are no real leaders among the handful of proponents of steady s
Re:Yellow Diarrhea Will Work, says Planetary Socie (Score:2)
2) do a google image search for that word phrase with the filtering off.
3) feel eyes melt out of your skull in horror.
4) ????
5) profit.
Re:hi. (Score:2)
Sort of like the PC language Gestapo, only different. In public both can be easily identified by the small adhesive stamps worn on their lapels. The stamp has a upside-down lower case e printed on the stamp.
By their schwa stickers ye shall know them. (ducking)
Re:Cheap shot in the article? (Score:2)
I know it can be taken that way, but I think the writer, Louis Freedman, is actually just skilled at rhetoric. As director of the Planetary Society, we would expect this.
Freedman immediately acknowledges that Gold is a professor at a prestigious university whom he (Freedman) has studied under and learned much from. Freedman states that Gold does occa