Dyson spheres; dark matter

[David Gould]

A friend of mine suggested that the widespread existence of Dyson spheres in our and other galaxies might be an explanation for why we cannot see 90 per cent of the matter that we know - from gravitional evidence - exists.

I understand that the heat energy from the stars covered by Dyson spheres would still need to be dispersed (otherwise the Dyson spheres would melt!). However, if it was done as heat energy, would that be readily detectable from a distance? We can see stars because they emit visible light. We can also detect various other forms of radiation - radio waves, gamma waves et cetera. But is infra-red radiation as easy to spot?

 

[David Gould]

http://teacherlink.ed.usu.edu/tlnasa/pictures/litho/infrared/infrared.html

Easy, I guess! That disproves that idea.

 

[variant]

A friend of mine suggested that the widespread existence of Dyson spheres in our and other galaxies might be an explanation for why we cannot see 90 per cent of the matter that we know - from gravitional evidence - exists.

I understand that the heat energy from the stars covered by Dyson spheres would still need to be dispersed (otherwise the Dyson spheres would melt!). However, if it was done as heat energy, would that be readily detectable from a distance? We can see stars because they emit visible light. We can also detect various other forms of radiation - radio waves, gamma waves et cetera. But is infra-red radiation as easy to spot?

The theory would only work if such technological societies were hugely numerous (almost beyond comprehension), and had a way of storing all that heat and energy instead of dissipating it, and thus leaving no external sign.

 

[azmurath]

I think that if Dyson Spheres were being created, dont you think we would notice the stars just disappearing one day? I believe in ET intelligence, just nothing advanced to the point of being a type 2 civilization.

 

[David Gould]

I think that if Dyson Spheres were being created, dont you think we would notice the stars just disappearing one day? I believe in ET intelligence, just nothing advanced to the point of being a type 2 civilization.

Not really. We have only been watching the skies in detail for about 4,000 years, and we have only been able to use infrared astronomy for the past 200 years, and only in the last few decades have we been able to overcome the problems our atmosphere causes.

It is incredibly unlikely that we would have observed the act of the creation of a dyson sphere, even if there were a trillion of them through the galaxy. At a rate of 20 a year for the past five billion years, we would only have been really able to see a few thousand or so at most - and more likely a few hundred. And that assumes a constant rate and that it is still going on.

But the heat energy thing is, I think, a huge stumbling block to the idea.

If aliens exist, why would you assume that no type 2 civilisations exist? Very likely in 100,000 years or so we will be a type 2 civilisation, assuming we survive that long.

If the galaxy has been around for about 10 billion years, any civilisation that arose more than say a million years before us should be a type 2 civilisation by now. And a million years is a blip in time compared to 10 billion years.

My personal feeling is that Fermi's paradox is pretty difficult to get around - for our galaxy, at any rate. If intelligent life arises easily enough for, say, 5 intelligent species to get into space, in 10 billion years, where are they? The first one to arise should be everywhere, given a 50 million year headstart or so.

 

[Paulos23]

The speed of light is one limiter against the spread of a intelligent species across the universe. Another is the number of planets that are habbitable to them and how frequent they are. If the nearest habbitable planet was across the galaxy it would be a while before you bothered.

Besides, space is huge and time is vast. Several intelligent species could have come and gone and we wouldn't have known it.

 

[David Gould]

The speed of light is one limiter against the spread of a intelligent species across the universe.

But not across the galaxy. Assuming that a speed of .1 per cent of the speed of light is reached, it would take only 100 million years for a race to spread throughout the entire galaxy (and that is assuming they started from one edge - the closer they are to the centre, the shorter the time for expansion.) If they got up to a speed such as two per cent of the speed of light and were close to the centre, it would take less than five million years.

Another is the number of planets that are habbitable to them and how frequent they are. If the nearest habbitable planet was across the galaxy it would be a while before you bothered.

But already we have the technology to build artificial environments that enable us to survive in space. And even to terraform other planets to suit us. In 100 thousand years, such technology is going to be incredible. As such, other habitable planets are not really an issue - resources are, though.

Besides, space is huge and time is vast. Several intelligent species could have come and gone and we wouldn't have known it.

This is precisely my point, though. With the galaxy so big and time so long, if intelligence is relatively easy to come by - say, five such species every 10 billion years or so - then we should see evidence that many parts of the galaxy have been technologisised. Assuming we survive, in 50 million years there will be a lot of evidence for us in much of the galaxy. And that evidence will not simply disappear if we die out.

 

[azmurath]

Not really. We have only been watching the skies in detail for about 4,000 years, and we have only been able to use infrared astronomy for the past 200 years, and only in the last few decades have we been able to overcome the problems our atmosphere causes.

It is incredibly unlikely that we would have observed the act of the creation of a dyson sphere, even if there were a trillion of them through the galaxy. At a rate of 20 a year for the past five billion years, we would only have been really able to see a few thousand or so at most - and more likely a few hundred. And that assumes a constant rate and that it is still going on.

But the heat energy thing is, I think, a huge stumbling block to the idea.

If aliens exist, why would you assume that no type 2 civilisations exist? Very likely in 100,000 years or so we will be a type 2 civilisation, assuming we survive that long.

If the galaxy has been around for about 10 billion years, any civilisation that arose more than say a million years before us should be a type 2 civilisation by now. And a million years is a blip in time compared to 10 billion years.

My personal feeling is that Fermi's paradox is pretty difficult to get around - for our galaxy, at any rate. If intelligent life arises easily enough for, say, 5 intelligent species to get into space, in 10 billion years, where are they? The first one to arise should be everywhere, given a 50 million year headstart or so.

Yes, but the barrier from type 1 to type 2 is incredibly hard to break. Right now humanity is at about .7 on the scale, and we are planned to break the type 1 barrier in about 50-200 years, if we do not kill ourselves first. Using all the energy from a planet is one thing, from an entire solar system is another. We are not even sure it can be done.

 

[David Gould]

Yes, but the barrier from type 1 to type 2 is incredibly hard to break. Right now humanity is at about .7 on the scale, and we are planned to break the type 1 barrier in about 50-200 years, if we do not kill ourselves first. Using all the energy from a planet is one thing, from an entire solar system is another. We are not even sure it can be done.

I cannot think of any barriers to doing so. As I said, in 100,000 years - or in a million years - why wouldn't we be able to do so?

 

[azmurath]

I cannot think of any barriers to doing so. As I said, in 100,000 years - or in a million years - why wouldn't we be able to do so?

I dont know really. Maybe there is just a technological cap, we can only go so far with the resources we have available. To me it seems that we would need the power contained by a Dyson sphere to actually build a Dyson sphere, so which came first, Dyson sphere 1 or Dyson sphere 2?

 

[KerrMetric]

A friend of mine suggested that the widespread existence of Dyson spheres in our and other galaxies might be an explanation for why we cannot see 90 per cent of the matter that we know - from gravitional evidence - exists.

Think about the silliness of the idea for a second. You want small mass spheres around a star to somehow account for 9 times the mass of the stars and dust and gas we see.

Doesn't this seem a tad unlikely?

I understand that the heat energy from the stars covered by Dyson spheres would still need to be dispersed (otherwise the Dyson spheres would melt!). However, if it was done as heat energy, would that be readily detectable from a distance? We can see stars because they emit visible light. We can also detect various other forms of radiation - radio waves, gamma waves et cetera. But is infra-red radiation as easy to spot?

Infra-red is easier to detect really than optical. The best way of detecting Dyson Spheres (which by the way are probably not feasible for other reasons) is to look for the differential flux between the 12 micron and the K band (2.2 micron) wavelengths.

 

[Logic_Fault]

My personal feeling is that Fermi's paradox is pretty difficult to get around - for our galaxy, at any rate. If intelligent life arises easily enough for, say, 5 intelligent species to get into space, in 10 billion years, where are they? The first one to arise should be everywhere, given a 50 million year headstart or so.

You're making the assumption that the other species would be as adventurous as humans. Perhaps they're highly xenophobic and avoid any contact with other species or simply not interested in other cultures for whatever reason. Just because we humans are extremely curious and driven to explore doesn't mean all species would be.

Or maybe they're a lot like us and they're just too busy fighting amongst themselves to go looking for someone else.

 

[David Gould]

You're making the assumption that the other species would be as adventurous as humans. Perhaps they're highly xenophobic and avoid any contact with other species or simply not interested in other cultures for whatever reason. Just because we humans are extremely curious and driven to explore doesn't mean all species would be.

Or maybe they're a lot like us and they're just too busy fighting amongst themselves to go looking for someone else.

Some will be more adventurous than humans, some won't be. Some will be more agressive than humans, some won't be. And they may well be other reasons that force them into space - the need for resources being one.

And it does not really matter about avoiding contact with other species - if they exist and have spread through the galaxy, we would be able to tell by the changes they have wrought to the galaxy through technology. They would not need to contact us for us to find out about them.

 

[David Gould]

I dont know really. Maybe there is just a technological cap, we can only go so far with the resources we have available. To me it seems that we would need the power contained by a Dyson sphere to actually build a Dyson sphere, so which came first, Dyson sphere 1 or Dyson sphere 2?

If we were in 10 solar systems, using 1/10th of the power of each, we would have enough power to build a Dyson sphere.

And we would build it in bits in any case. Assume it took 1,000 years of energy to build 1 per cent of a Dyson Sphere. In 100,000 years, we could have built one.

 

[David Gould]

Think about the silliness of the idea for a second. You want small mass spheres around a star to somehow account for 9 times the mass of the stars and dust and gas we see.

Doesn't this seem a tad unlikely?

Not unlikely if the galaxy is basically technologisised. And it could account for some of the dark matter.

Infra-red is easier to detect really than optical. The best way of detecting Dyson Spheres (which by the way are probably not feasible for other reasons) is to look for the differential flux between the 12 micron and the K band (2.2 micron) wavelengths.

Excellent. Thanks. What are the other reasons that Dyson Spheres are not feasible? (By the way, I think that even if it is practical to build them, I cannot see the attraction, given all the energy out in the galaxy in any case).

 

[BVZ]

I dont think you need a sphere to build another one. If you build 1 km^2 of 1 sphere, that would provide enough energy to build the next 1 km^2 and so on. It will grow exponentially. The more energy you have, the more you can build, the more energy you have.

 

[KerrMetric]

Not unlikely if the galaxy is basically technologisised. And it could account for some of the dark matter.

Beyond unlikely - probability zero for several reasons.

First reason is the fact the hypothesised sphere would have negligible mass when compared to a star.

Second reason is that we know the approximate distribution of dark matter and it is not where the stars are.

Third reason is that Dyson spheres would radiate like hell at 12 microns. They are NOT dark in the slightest.

Excellent. Thanks. What are the other reasons that Dyson Spheres are not feasible? (By the way, I think that even if it is practical to build them, I cannot see the attraction, given all the energy out in the galaxy in any case).

How does the Dyson sphere maintain its position relative to the star?
What material would be feasible as the major component of the structure? Hint: There isn't one.

 

[azmurath]

I dont think Dyson Spheres are being built, nor will they ever be built, however I do see huge rings like those in the Larry Niven Ringworld novels perhaps being built one day.

 

[gluadys]

One calculation which I see missing from discussions on possible alien civilizations is when would life become feasible the universe?

Many alien civilization scenarios seem to assume a static universe where civilizations could crop up at any point of time.

But in a dynamic universe initiated by a big bang, that is not the case. No life, no civilization could have emerged before stars emerged, for example.

Our solar system is a second or third generation system as evidenced by the supply of heavy elements in the system, which must have been generated by a prior supernova.

Could life -- any life-- form in a first generation system lacking these elements?

I would be interested in some calculations that would indiciate at what point in the expansion of the universe life first becomes possible. Maybe alien civilizations can't have as much of a head start on us as some people are speculating.

 

[And-U-Say]

A friend of mine suggested that the widespread existence of Dyson spheres in our and other galaxies might be an explanation for why we cannot see 90 per cent of the matter that we know - from gravitional evidence - exists.

I understand that the heat energy from the stars covered by Dyson spheres would still need to be dispersed (otherwise the Dyson spheres would melt!). However, if it was done as heat energy, would that be readily detectable from a distance? We can see stars because they emit visible light. We can also detect various other forms of radiation - radio waves, gamma waves et cetera. But is infra-red radiation as easy to spot?

Interesting, but a massive IR signature would be easy to detect. So as much as I like the idea, I don't hink that its the case.