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Cosmologist
2012-Dec-11, 12:00 AM
If other civilisations are already conversing with laser transmissions it would be impossible to detect those signals unless they went right past our planet. Couldn't we tap into the sun for power? I'm picturing a giant space laser. Mirrors focusing sunlight to stimulate ruby crystal or argon gas or whatever lasers use nowadays? I'm trying to imagine the most common method used in the universe. If we can imagine lasers for communicating between stars then I'm sure others have already done it. Maybe millions of years ago. Laser signals might be crisscrossing the universe like a giant web. I guess the only way to catch one would be sending a probe between two likely candidate stars and hoping for the best.

Remember that 'WOW' signal years back. Maybe a rogue black hole briefly bent a laser transmission out of shape and we eavesdropped on someone elses telephone call.

Most habitable stars are outside the core and inside the rim of the galaxy right. Stars are constantly moving so transmissions must be too. Maybe if we concentrated on dense clusters of stars.

TooMany
2012-Dec-11, 12:09 AM
I believe the "WOW" signal was radio. Anyhow, how hard is it to imagine that, if an advanced civilization wanted to, they could build thousands of space-based lasers aimed at thousands of systems in an attempt to establish communication?

Their star might be a useful power source. However, if (for example) very simple and efficient fusion power were available they might prefer to use that rather than gathering star light with large, expensive mirrors.

Cosmologist
2012-Dec-11, 12:31 AM
'Light and radio are just different parts of the electromagnetic spectrum so wouldn't there be a little radio included in such a powerful laser? I really have no idea.

Simple and efficient fusion power is probably a pipe dream. If it was simple we would have discovered it already. If it was efficient then we wouldn't be pouring more power into running a typical fusion reactor than it actually produces.

How expensive are shiny surfaces? Mylar is good and compact. Glass mirrors actually absorb a lot of light.

Amazing how astronomers can predict where a star will be in a few years when a laser transmission arrives. Stars change position in the sky so slowly you wouldn't think they could extrapolate their future positions so accurately. A laser will widen a lot by the time it reaches its destination. Catching a signal not meant for us that has overshot its target would require a big reflector or array.

TooMany
2012-Dec-11, 12:46 AM
'Light and radio are just different parts of the electromagnetic spectrum so wouldn't there be a little radio included in such a powerful laser? I really have no idea.

No there would not be unless some distortion of the signal occurred. With laser's you are talking about coherent waves that are extremely short in comparison with the radio spectrum. The band spread is tiny in comparison with the frequency.


Simple and efficient fusion power is probably a pipe dream. If it was simple we would have discovered it already. If it was efficient then we wouldn't be pouring more power into running a typical fusion reactor than it actually produces.


Well simple, probably not. Are you yet another progress pessimist? Because we've tried for a while and failed, it's impossible? There seem to be a surprising number of pessimists around considering the science fiction like subject matter in these forums.

Cosmologist
2012-Dec-11, 01:08 AM
Not a pessimist. A realist. Because we've tried for a very long time and failed miserably. I personally don't think a suitcase sized fusion power generator will ever exist. A power plant for cities is unlikely. An engine for a colossal starship possibly. We have fusion now. Its just not steady. Hydrogen bombs exist. They could be used to power things. Its just not practical, simple or efficient.

Fusion generators might happen but it seems improbable to me. Just my opinion. The sun is a natural fusion power generator. Not sure how close we could send the laser and mirrors but don't you think most chatty sentient species would use their own sun to power a transmitter. Its already the biggest transmitter they have.

How about using the sun as a transmitter? Like old morse code. Build a Dyson Sphere around the sun to control its output.

cjameshuff
2012-Dec-11, 01:13 AM
Simple and efficient fusion power is probably a pipe dream. If it was simple we would have discovered it already. If it was efficient then we wouldn't be pouring more power into running a typical fusion reactor than it actually produces.

There's a simple explanation for the "failure" of fusion power.

http://commons.wikimedia.org/wiki/File:U.S._historical_fusion_budget_vs._1976_ERDA_p lan.png

It's incredible that we've made as much progress as we have...even small scale fusion research projects are constantly being shut down due to lack of funding, and you simply can't build full-scale power producing reactors on the pittance of research funding we've devoted to the problem. And in fact, fusion research projects have generally been successful at developing and demonstrating the needed technologies, and we are finally building a large scale reactor that is expected to produce power:
http://en.wikipedia.org/wiki/ITER

So no, it's not a pipe dream, and given its success even while so absurdly underfunded, probably easier than originally feared.

Cosmologist
2012-Dec-11, 02:01 AM
Didn't Oppenheimer or Dyson give a similar speech in their youth? :rimshot:

TooMany
2012-Dec-11, 05:40 PM
There's a simple explanation for the "failure" of fusion power.

http://commons.wikimedia.org/wiki/File:U.S._historical_fusion_budget_vs._1976_ERDA_p lan.png

It's incredible that we've made as much progress as we have...even small scale fusion research projects are constantly being shut down due to lack of funding, and you simply can't build full-scale power producing reactors on the pittance of research funding we've devoted to the problem. And in fact, fusion research projects have generally been successful at developing and demonstrating the needed technologies, and we are finally building a large scale reactor that is expected to produce power:
http://en.wikipedia.org/wiki/ITER

So no, it's not a pipe dream, and given its success even while so absurdly underfunded, probably easier than originally feared.

Whenever people say no-way they hint that their motives are suspect, i.e. biased (for some unstated reason) against the realization of possibilities. This attitude is justified by self-designation as "realist" or "pragmatist". IMO such a view is pathological form of skepticism that fortunately does not dominate human endeavors.

There are some who may correctly argue that the ITER concept is impractical, even if it does succeed. I can't render a meaningful opinion. There are in fact several other paths to fusion that might pan out, but they get very little funding in comparison with ITER. It seems as if the fusion researchers have put almost all of their eggs in one basket.

cjameshuff
2012-Dec-11, 06:36 PM
There are some who may correctly argue that the ITER concept is impractical, even if it does succeed. I can't render a meaningful opinion. There are in fact several other paths to fusion that might pan out, but they get very little funding in comparison with ITER. It seems as if the fusion researchers have put almost all of their eggs in one basket.

There's not really any other option. R&D costs money, and there's not enough for much diversity in approaches. The difficulty of obtaining funding for a risky new approach and the potential of having it cut off if costs are unexpectedly high or if early results are inconclusive make for strong motivation to stick close to what's known to work.

The ITER tokamak is probably quite sub-optimal, there's been a lot of proposals for refinement of the basic tokamak design and basically similar approaches like the stellarator. And the Polywell seems to be holding up to the theoretical predictions, which would make it a much better approach. But ITER should still produce power, which will hopefully help convince people to stop starving fusion research of funding.

TooMany
2012-Dec-11, 07:51 PM
There's not really any other option. R&D costs money, and there's not enough for much diversity in approaches. The difficulty of obtaining funding for a risky new approach and the potential of having it cut off if costs are unexpectedly high or if early results are inconclusive make for strong motivation to stick close to what's known to work.

The ITER tokamak is probably quite sub-optimal, there's been a lot of proposals for refinement of the basic tokamak design and basically similar approaches like the stellarator. And the Polywell seems to be holding up to the theoretical predictions, which would make it a much better approach. But ITER should still produce power, which will hopefully help convince people to stop starving fusion research of funding.

Yes we need some proof at least in experiment to keep things moving. However, I disagree that we should put all our funding into ITER. The argument seems to be "look how much we have already spent on this approach, we cannot turn back now". I think you will find that the fraction of resources devoted to other approaches like Polywell and Focus fusion are tiny by comparison. The Navy is funding Pollywell under much secrecy concerning the results but dedicating about 2.5 million per year currently (a mere drop in the bucket of the Pentagon's budget). The ITER experiment is projected to cost $15 billion or 6,000 times the current annual spending on Pollywell. Goodness, what is wrong with this picture?

Meanwhile every year we spend $700 billion on oil not to mention coal and natural gas. I guess I've wandered far from the subject.

neilzero
2012-Dec-12, 10:32 PM
Let's suppose Centari B has a planet with a slightly more advanced civilization than Earth. They have hundreds of colonies and outposts within about 0.043 light years. They use a solar power satellite at a cancelled gravity point to broadcast wide band laser to several of the outposts at a time then switch directions many times per 0.775226 Earth year so each colony and outpost receives the broadcasts on a brief but random schedual. Most of the time the laser is not pointed at Earth, but occasionally it is for a few minutes. Earth is 100 times farther than the most distant intended viewer and listener, so the signal is 10,000 times weaker = square law. A telescope such as Hubble can detect the signal if Hubble is pointing at Cantari B during the brief transmission window, but it is close to the noise level and no one on Earth knows the data algorithm, so we have near zero chance of converting the data to English or pictures. The problems are much the same if the Centarians use microwaves instead of lasers, except we would detect the signal with the Aricibo radio telescope or equivelent. Likely the Centurians are transmitting about one gigawatt in a beam about one degree wide, so the beam almost always misses Earth and might not repeat for years, even though the effective radiated power is many terawatts, so the Cetarians only need a small recever such as a Ipod. Much less power is needed for narrow band transmissions, but long range, narow band transmissions may be very rare in Centarian technology. Neil