Science
15 Oct 15
17 Oct 15
Originally posted by sonhouseThe whole point of a dyson sphere is to process and use the energy from the star. I believe emitting heat in the form of IR radiation is a practical requirement that cannot be avoided. Its a second law of thermodynamics thing. And no, you could not use the IR as a secondary energy source, nor cool the outside to 3 degrees K.
The bit about giving off IR could be countered by IR reflective surfaces, effectively hiding all IR. We are getting pretty advanced in stealth technology and I would think a problem like that would be turned into an advantage, using the IR as an extra energy source. The outside could look like the cosmic background, 3 odd degrees K.
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17 Oct 15
Originally posted by sonhouseThere is no such thing as stealth in space.
The bit about giving off IR could be countered by IR reflective surfaces, effectively hiding all IR. We are getting pretty advanced in stealth technology and I would think a problem like that would be turned into an advantage, using the IR as an extra energy source. The outside could look like the cosmic background, 3 odd degrees K.
A Dyson Sphere works by converting low entropy light into high entropy light and using
that change to do work.
The 'temperature' of the radiation will depend on the size of the sphere, the larger it is then
the 'cooler' it will appear.
BUT
The total power out will be the same as the power output of the star, so no mater what frequencies
it is radiating at, it will still shine just as bright as the star it surrounds.
I was going to post a link to a relevant article on the excellent Atomic Rockets website...
But it appears not to be working right now.
I will post a link when it comes back up
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17 Oct 15
Originally posted by twhitehead
I did not know that. Interesting. Does it apply to a ring too?
[b]..... displacement that could be very hard to control ...
But it could be done by letting varying amounts of energy through the sphere ....
lso you need to have enough solar cells to make this possible and they use rare earths.
I doubt that all solar cells require rare ea ...[text shortened]... ability there is no good reason to think a dyson sphere or any other alien activity is involved.[/b]
I think the real giveaway is that there is no good reason to think a dyson sphere would emit variable amounts of radiation unless it was being used for signalling. So unless we see a message in the variability there is no good reason to think a dyson sphere or any other alien activity is involved
The suggestion is an 'incomplete' Dyson Sphere, or other mega-structure, which would cause variable
amounts of radiation to be 'emitted'.
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17 Oct 15
2 edits
Originally posted by twhiteheadWeeeelll... Kinda.
The whole point of a dyson sphere is to process and use the energy from the star. I believe emitting heat in the form of IR radiation is a practical requirement that cannot be avoided. Its a second law of thermodynamics thing. And no, you could not use the IR as a secondary energy source, nor cool the outside to 3 degrees K.
You can [theoretically] extract energy as long as you have a temperature differential.
The smaller the differential the less efficient your energy extraction will be, and, crucially
the larger the radiator you need to dump the waste heat to space.
Radiated Energy follows this formula E = [SB] * T^4
Where E is Energy [Watts, W]
[SB] is the Stefan-Boltzmann constant [W m-2 K-4] [5.67E-8]
And T is Temperature [Kelvin, K]
This means that to dump waste heat with the power of a star, you need a very large radiator,
or very large temperatures.
Now a 1 AU Dyson Sphere [which I will just call a 'Sphere' {always capitalized} from now on]
Does have a very large surface area...
However for a star with the same power output as our Sun, [the one we are discussing is bigger]
a 1 AU Sphere will radiate at ~394K
If you want to get remotely close to 3K... [You can't actually get to background temp or below as
then you become a net energy absorber, rather than radiator, and most galaxies have temps between
10k and 100K...]
Well at 1000 freaking AU the Sphere would still radiate at over 12K...
[EDIT: at 60,000 AU the temp drops to ~2.8K, but the formula I am using is probably broken that close to the CMB at 2.728K]
Given that building a 1 AU Sphere requires sacrificing all the inner planets [except Earth] and several
of the outer ones to provide the matter required.....
This article has a discussion of space radiators, with an errata that it misses off the *10^-8 from the
Stefan-Boltzmann constant.
http://www.nss.org/settlement/nasa/spaceresvol2/thermalmanagement.html
So it's obviously not practical to build a Sphere that radiates at 3K, but if the universe were cool enough
there is nothing thermodynamically stopping you...
18 Oct 15
Originally posted by googlefudgeYes, but any such irregular structure suffers from the same problems that non alien structures do ie that they should still show a regular signal if they are in uniform orbit, but if they are not, then why not.I think the real giveaway is that there is no good reason to think a dyson sphere would emit variable amounts of radiation unless it was being used for signalling. So unless we see a message in the variability there is no good reason to think a dyson sphere or any other alien activity is involved
The suggestion is an 'incomplete' Dyson ...[text shortened]... ere, or other mega-structure, which would cause variable
amounts of radiation to be 'emitted'.
My own feeling is that it is either activity (nonalien) on the stars surface itself, or it is dust so far out that we haven't yet watched it for a full period.
18 Oct 15
Originally posted by twhiteheadIt can't be dust due to the absence of an infra-red signal.
Yes, but any such irregular structure suffers from the same problems that non alien structures do ie that they should still show a regular signal if they are in uniform orbit, but if they are not, then why not.
My own feeling is that it is either activity (nonalien) on the stars surface itself, or it is dust so far out that we haven't yet watched it for a full period.
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18 Oct 15
Originally posted by DeepThoughtIndeed.
It can't be dust due to the absence of an infra-red signal.
And as for activity on the stars surface....
I'm intrigued as to what could possibly cause a 22% drop in luminosity without any
change in surface temperature on an established and stable star.
[given that the authors have already ruled out sunspots and other known stellar phenomena]
18 Oct 15
Originally posted by googlefudgeSuch a sphere could radiate into space at holes in the sphere where the radiation captured needs to be radiated away. They could choose an angle of radiation that would lead to nothing in the galaxy so stay hidden.
Weeeelll... Kinda.
You can [theoretically] extract energy as long as you have a temperature differential.
The smaller the differential the less efficient your energy extraction will be, and, crucially
the larger the radiator you need to dump the waste heat to space.
Radiated Energy follows this formula E = [SB] * T^4
Where E is Energy [Watts, W ...[text shortened]... at 3K, but if the universe were cool enough
there is nothing thermodynamically stopping you...
I think a civilization advanced enough to capture an entire sun's energy could figure out a way to keep the whole thing at 3 degrees K, such as radiating through a hole in the north or south pole of the construct.
18 Oct 15
Originally posted by googlefudgeI've skim read the paper and I mean skim read. There are a number of alternatives discussed - along with the associated problems with each of them. One thing the article does not mention is that the star has a companion, which changes things a little. The star is on the main sequence and F type, so only slightly bigger than the sun. The paper seems to be saying that there are a number of possible explanations none of which quite fit the data; one option is a new class of variables, Dyson spheres and alien civil engineering projects aren't mentioned in the paper - I suspect that is more of a way of getting the media interested than a serious suggestion.
Indeed.
And as for activity on the stars surface....
I'm intrigued as to what could possibly cause a 22% drop in luminosity without any
change in surface temperature on an established and stable star.
[given that the authors have already ruled out sunspots and other known stellar phenomena]
18 Oct 15
1 edit
Originally posted by DeepThoughtWhile we can speculate about aliens and such, it is just a thought experiment. The real chances of those variances being due to aliens is slim to none.
I've skim read the paper and I mean skim read. There are a number of alternatives discussed - along with the associated problems with each of them. One thing the article does not mention is that the star has a companion, which changes things a little. The star is on the main sequence and F type, so only slightly bigger than the sun. The paper seems t ...[text shortened]... per - I suspect that is more of a way of getting the media interested than a serious suggestion.
I don't buy the clouds of comet theory, I think there would be more regularity in those readings. It would have to be a huge cloud but that doesn't account for the wide timing swings, 800 days one time 1200 the next and who knows the timing of the next one.
Can anyone do the math of how far away a Jupiter size planet would have to be to eclipse 20 odd percent of that star's light? Obviously OUR Jupiter could totally occlude that star if it got in the line of sight and obviously if Jupiter was say a million Km away from that star during occultation, it could not possibly knock out 20 percent of that starlight. But if it was a LOT further from that sun it could occlude the whole thing. But the question is, how far out would that be?
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18 Oct 15
Originally posted by DeepThoughtDid you try reading the bad astronomy link I posted which says EXACTLY what this is?
I've skim read the paper and I mean skim read. There are a number of alternatives discussed - along with the associated problems with each of them. One thing the article does not mention is that the star has a companion, which changes things a little. The star is on the main sequence and F type, so only slightly bigger than the sun. The paper seems t ...[text shortened]... per - I suspect that is more of a way of getting the media interested than a serious suggestion.
As opposed to you guessing?
http://www.slate.com/blogs/bad_astronomy/2015/10/14/weird_star_strange_dips_in_brightness_are_a_bit_baffling.html
[/quote]A paper by a team of astronomers is getting some notice because of aliens.
Now let’s have a care here. The paper doesn’t mention aliens, and it doesn’t even imply aliens. Not directly, at least. But the astronomers found a star so odd, with behavior so difficult to explain, that it’s clear something weird is happening there. And some of the astronomers who did the work are now looking into the idea that what they’ve found might (might!) be due to aliens.
But don’t let this idea run away with you (as it has with some folks on social media and, no doubt, will in some sketchier “media” outlets any minute now). The scientists involved are being very skeptical and approaching this the right way: more of an interested “Hey, why not?” follow-up, as opposed to the Hollywood renegade astronomer who just knows it’s aliens but (fist shaking in the air) just can’t convince those uptight Big Astro sellouts!
But it’s cool either way.
..................................................................
So where does that leave us?
Wondering if there might be more to this, Tabetha Boyajian, the lead author on the paper, showed the results to Jason Wright, an astronomer who studies exoplanets and, not coincidentally, has researched how to look for signatures of advanced alien civilizations in Kepler data.
Yes, seriously.
Get this:
Look at our own civilization. We consume ever-increasing amounts of power, and are always looking for bigger sources. Fossil, nuclear, solar, wind … Decades ago, physicist Freeman Dyson popularized an interesting idea: What if we built thousands of gigantic solar panels, kilometers across, and put them in orbit around the Sun? They’d capture sunlight, convert it to energy, and that could be beamed to Earth for our use. Need more power? Build more panels! An advanced civilization could eventually build millions, billions of them.
This idea evolved into what’s called a Dyson Sphere, a gigantic sphere that completely encloses a star. It was popular back in the 1970s and 80s; there was even an episode of Star Trek: The Next Generation about one. Dyson never really meant that we’d build an actual sphere; just lots of little panels that might mimic one.
But it raises an interesting possibility for detecting alien life. Such a sphere would be dark in visible light but emit a lot of infrared. People have looked for them, but we’ve never seen one (obviously).
Which brings us back to KIC 8462852. What if we caught an advanced alien civilization in the process of building such an artifact? Huge panels (or clusters of them) hundreds of thousands of kilometers across, and oddly-shaped, could produce the dips we see in that star’s light. ...........................
Look, I think it’s pretty obvious this scenario is, um, unlikely. But hey, why not? It’s easy enough to get follow-up observations of the star to check the idea out. It’s low probability but high stakes, so probably worth a shot. And it’s not exactly science fiction; Wright and a few other astronomers have submitted a paper (pending publication) to the prestigious Astrophysical Journal examining the physics of these structures and detailing how they could be detected around other stars. .................
[/quote]
18 Oct 15
Originally posted by twhiteheadI don't think that sonhouse's idea is ludicrous - o.k. I think Dyson Sphere's are a ludicrous idea but since that's what we're discussing...
The whole point of a dyson sphere is to process and use the energy from the star. I believe emitting heat in the form of IR radiation is a practical requirement that cannot be avoided. Its a second law of thermodynamics thing. And no, you could not use the IR as a secondary energy source, nor cool the outside to 3 degrees K.
What determines the external temperature of our sphere is the temperature of the universe (~3K) and the temperature of the inside, as well as heat conductivity and the thickness of the shell. If they can build one of these things then it is entirely plausible to me that they'll have some way of making the temperature gradient across the shell high enough that the external temperature is close to the temperature of the microwave cavity we all live in. While I don't think it's easy from an engineering point of view I don't think that it's impossible either. This one's a materials problem I think is solvable.
Again this statement applies to a rigid object of the kind that sonhouse is discussing rather than the more loose arrangement that googlefudge advocates. I wonder if anyone has checked that there isn't a microwave hotspot there?
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18 Oct 15
1 edit
Originally posted by DeepThoughtIt's not so much that I am advocating for a loose arrangement, it's more that such an
I don't think that sonhouse's idea is ludicrous - o.k. I think Dyson Sphere's are a ludicrous idea but since that's what we're discussing...
What determines the external temperature of our sphere is the temperature of the universe (~3K) and the temperature of the inside, as well as heat conductivity and the thickness of the shell. If they can build o ...[text shortened]... oglefudge advocates. I wonder if anyone has checked that there isn't a microwave hotspot there?
arrangement is physically possible, as opposed to the shell idea which isn't.
However, no matter how much thermal shielding you have, the power in must equal
power out. As such you must have a radiator large enough to radiate 1 stars energy
at your desired temperature, which as I just demonstrated, is ludicrously large for
temperatures around 3K. for a 1Au structure the number is over 300K which means
you are looking at IR wavelengths.
As for looking for microwaves...
Not yet, that is what the requested follow up observations, looking for radio and other
frequencies to get more data.
EDIT: Ahah, and as it's now working again, here is the invaluable Atomic Rockets
on why thermodynamics says you can't have stealth in space.
http://www.projectrho.com/public_html/rocket/thermodynamics.php
http://www.projectrho.com/public_html/rocket/spacewardetect.php#id--Why_Not?_Let_me_count_the_ways--What_If_I_Run_Silent_And_Cold?
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18 Oct 15
3 edits
Originally posted by sonhouseI'm not really use to solving problems involving these distances,and light, etc. but to me it seems to be pretty standard trigonometry with the assumptions I made so I'll try, perhaps someone can confirm or refute the model.
While we can speculate about aliens and such, it is just a thought experiment. The real chances of those variances being due to aliens is slim to none.
I don't buy the clouds of comet theory, I think there would be more regularity in those readings. It would have to be a huge cloud but that doesn't account for the wide timing swings, 800 days one time 12 ...[text shortened]... from that sun it could occlude the whole thing. But the question is, how far out would that be?
D = diameter of the star
d = diameter of the planet
x = distance from the star to the earth
x' = distance from the star to the planet
P = percent of blocked light by planet at distance x' from the star
D' = the diameter of the cross-section at distance x' from the star
Assume:
(1) the star,planet, and the earths centers are co-linear.
(2) the Earths diameter is much smaller than the star such that the earth can be modeled as a point.
(3) the light blocked is proportional to any cross-sectional area at x' of the cone with base "D", and height "x".
Let "O" be the center of the earth
"A" be the center of the star
"B" be a point on the surface of the star, such that OAB is a right triangle.
Let A' be the center of the Planet and B' be the intersection of line OB and a line drawn from A' perpendicular to line OA'
From similar triangles
(D/2 - D' /2 )/x' = D' /(2*( x-x' ))
Solve the above for x'
x' = x*(D'/( D - D' )+1)^(-1) Equation 1
Now get D' in terms of d, and the percent light blocked P start with:
Pi*(d/2)^2 = Pi*( P/100 )*(D'/2)^2
D' = d/(Sqrt( 100/P )) Equation 2
Sub Equation 2 into Equation 1
x' = x*(d/(Sqrt(100/P ))/(D - d/(Sqrt( 100/P )))+1)^(-1)
Plug in the appropriate values and the required distance of the planet from the sun to block P percent of the light to the earth should pop out...I think.