Scientific American: If There Are Aliens Out There, Where Are They?

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Profile Bob DeWoody
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Message 1761878 - Posted: 3 Feb 2016, 13:05:56 UTC

FTL travel, if possible, is the key to it all. Otherwise searching for ET, intelligent or otherwise is purely an academic exercise. Without FTL travel any expedition to another star system is a one way trip for colonization. Even then, earth and the colonized planet will not be able to maintain meaningful contact.
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Message 1761904 - Posted: 3 Feb 2016, 14:38:51 UTC - in response to Message 1761901.  

The clue is to fool physics into thinking you have zero mass, then the restriction won't apply. Solve that one and FTL is there.


I don't think so. Even with zero mass, there is no way to accelerate beyond light speed. If you need a force such that with every action, there is an equal and opposite reaction, and no force exists to create that reaction, then mass doesn't matter.

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Message 1761909 - Posted: 3 Feb 2016, 14:57:17 UTC

This (from 2000) made an interesting read then.

negative energy

I am not sure how well it has stood up to scrutiny in the last 15 years though.
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Message 1761940 - Posted: 3 Feb 2016, 16:56:32 UTC

I don't think so. Even with zero mass, there is no way to accelerate beyond light speed. If you need a force such that with every action, there is an equal and opposite reaction, and no force exists to create that reaction, then mass doesn't matter.
....in this universe, or 'brane', if you remove the mass to be transported from this universe(Alcubierre)the laws of physics may not apply.

To Bob's point about FTL travel, it's more tragic than not being able to get there. When we get the provable WOW, we won't be able to have a discourse even if we understand each other due to time lag(50 years between question and answer?). Hopefully the WOW will contain detailed instructions for a quantum entanglement comm device...........":D>

"Sour Grapes make a bitter Whine." <(0)>
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Message 1761948 - Posted: 3 Feb 2016, 17:38:00 UTC

A photon is a mass-less particle. If you add more energy to it, it just has more energy, but doesn't go any faster. Even light speed is tricky to obtain. Some of the best ship designs I have read about would only achieve about 85% light speed. most are around 15%. Interstellar travel does seem extremely difficult, but intergalactic travel seems inconceivable.

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Message 1762036 - Posted: 4 Feb 2016, 1:07:28 UTC - in response to Message 1761878.  

FTL travel, if possible, is the key to it all. Otherwise searching for ET, intelligent or otherwise is purely an academic exercise. Without FTL travel any expedition to another star system is a one way trip for colonization. Even then, earth and the colonized planet will not be able to maintain meaningful contact.

This is why I enjoy watching The Expanse so much, an excellent sci-fi series with no fantasy, no FTL and no aliens.
So we never travel to the stars - so what? It would be cool if we could, just like it would be cool if I could live 500 years, but thinking that it's a tragedy because I won't would be silly. We have an entire system of planets and asteroids to play with and it's going to keep us busy for a very long time.
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Message 1762224 - Posted: 4 Feb 2016, 17:16:30 UTC - in response to Message 1762222.  

85% of light speed is quite acceptable. That means the nearest star could be reached in 5.3 years, say a 12 year round trip. So are these 85% designs feasible?


5.3 years if it doesn't takes years to accelerate up to speed and years to decelerate. That could possibly double, triple or more the time from what I understand.

Bob
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Message 1762231 - Posted: 4 Feb 2016, 17:36:36 UTC - in response to Message 1762222.  

85% of light speed is quite acceptable. That means the nearest star could be reached in 5.3 years, say a 12 year round trip. So are these 85% designs feasible?

Photons are traditionally said to be massless. This is a figure of speech that physicists use to describe something about how a photon's particle-like properties are described by the language of special relativity.

It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would introduce a small damping factor in the inverse square Coulomb law of electrostatic forces. That means the electrostatic force would be weaker over very large distances.

That is travel time for the astronauts. How many years pass on earth between departure and the return to earth?
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Message 1762240 - Posted: 4 Feb 2016, 17:47:32 UTC - in response to Message 1762222.  

85% of light speed is quite acceptable. That means the nearest star could be reached in 5.3 years, say a 12 year round trip. So are these 85% designs feasible?

The design I read about has a scoop almost the size of the moon, that looks like a radio dish. In space, these is about 1 atom of hydrogen per the volume of a grape fruit. The scoop would gather the hydrogen, then fuse it releasing energy. the vessel would be self refueling, but the size would be enormous. I keep wondering what would happen if a micrometeorite or larger object hit it somewhere.


5.3 years if it doesn't takes years to accelerate up to speed and years to decelerate. That could possibly double, triple or more the time from what I understand.


That is very true. I don't think the human form could withstand much more than 1 G for lengthy amounts of time. I think the idea of Star Wars ships just zipping around, even at normal speeds would tear a person to pieces.

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Message 1762242 - Posted: 4 Feb 2016, 17:52:24 UTC - in response to Message 1762231.  
Last modified: 4 Feb 2016, 17:53:08 UTC

Photons are traditionally said to be massless. This is a figure of speech that physicists use to describe something about how a photon's particle-like properties are described by the language of special relativity.

It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would introduce a small damping factor in the inverse square Coulomb law of electrostatic forces. That means the electrostatic force would be weaker over very large distances.
That is travel time for the astronauts. How many years pass on earth between departure and the return to earth?

At 85% light speed, there would be some relativistic effects, but not to bad. The real changes would be at over 95% light speed, increasing rapidly as light speed is approached.

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Message 1762246 - Posted: 4 Feb 2016, 17:59:30 UTC
Last modified: 4 Feb 2016, 18:02:22 UTC

I looked up both photon and neutrino in the Wikipedia and while finding that the photon is massless, the neutrino is having a small mass.

Both articles have apparently been updated and the article about the neutrino was a little surprise.

We have yet to discover the graviton, the particle which is assumed to be responsible for gravity.

If elementary particles could be used for propulsion, a photon could possibly be accelerated to near the speed of light without too much energy being needed. A neutrino would be slightly more difficult to do the same, because of its small mass.

Compare with fusion here on Earth. As far as I know, there have been no success at controlling fusion by means of reactors here on Earth.

If possible extraterrestrial craft are able to move and change direction by means of gravity amplifiers, in fact we should not be able to explain how energy is being produced in order for such a thing to be possible.

My guess is that fusion and the creation of energy by means of gravity is not the same.

Einstein's equation says that E=mc2, but in the same way as the body is able to produce heat from food, or even cold fusion for that matter, the only way a particle may be able to attain the speed of light is by assuming that it is representing pure energy rather than mass.

If so, rather than being a particle, it could be having the properties of a wave instead.

Perhaps someone having a better knowledge about physics could be able to explain this a little better.
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Message 1762360 - Posted: 5 Feb 2016, 5:03:28 UTC - in response to Message 1761830.  

We could send a focused beam back to anyone who told us where they were. We would send it at the same frequency that we received their message. We can command billion joule lasers but I am betting on microwaves.
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Message 1762634 - Posted: 5 Feb 2016, 20:27:55 UTC - in response to Message 1762421.  
Last modified: 5 Feb 2016, 20:46:43 UTC

The result that you cited was achieved in 2005. I have first hand knowledge from a retired scientist who worked at Lawrence Livermore Laboratory and can state that the number I put forth was correct. Laser output passed more than 1 billion Joules some time ago. The pulse was around one billionth of a second long.

These lasers are now intended for nuclear fusion research.
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Message 1762711 - Posted: 6 Feb 2016, 1:17:26 UTC - in response to Message 1762634.  

A joule is an energy unit. A billion joule seems too big to me. Maybe you mean a billion watt, given the very short time of the laser pulse.
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Message 1762726 - Posted: 6 Feb 2016, 2:09:14 UTC - in response to Message 1762711.  

A joule is an energy unit. A billion joule seems too big to me. Maybe you mean a billion watt, given the very short time of the laser pulse.
Tullio

I tend to agree, that would be a pretty big pile of energy, several kilotons of TNT.
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Message 1762739 - Posted: 6 Feb 2016, 3:30:36 UTC - in response to Message 1762726.  

A watt is a joule per second. Lasers are most commonly rated in Joules. They are building a Facility with joule in the title in Europe involving Lasers used in Fusion research.
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Message 1762801 - Posted: 6 Feb 2016, 9:00:50 UTC

AFAIK lasers are used in the optical interferometers such as LIGO in the USA, Virgo and Geo600 in Europe and one in Japan to detect gravitational waves. In the high power laser field Berkeley Livermore National Laboratory is the top, with a goal to attain nuclear fusion. Europe is going the tokamak way with JET and ITER, but also with Stellarator Wendelstein II in Germany, recently inaugurated by Angela Merkel, a physicist and Federal Republic of Germany Chancellor.
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Message 1762809 - Posted: 6 Feb 2016, 10:09:15 UTC - in response to Message 1762801.  

A laser's beam dispersion will be much less than the dispersion of microwaves.

Perhaps less power might be needed to communicate over long distances. Modulation techniques might be different.

Are we now looking for laser signals from our aliens. If so, what type of modulation do we expect.

All very good questions for those running a SETI project to answer.
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Message 1762837 - Posted: 6 Feb 2016, 12:08:41 UTC - in response to Message 1762815.  

Arecibo and Green Bank are radiotelescopes, they cannot get laser beams. But there is an optical telescope at Lick Observatory which can also send laser beams.
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Message 1762863 - Posted: 6 Feb 2016, 14:12:31 UTC - in response to Message 1762858.  

Arecibo has capabilities for sending a planetary radar beam, like the Goldstone antenna of NASA. They were recently used to watch an asteroid. The powerful laser beams of Livermore might be visible at great distances, but the Lawrence Livermore Laboratory has other things to do.
Tullio
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Message boards : SETI@home Science : Scientific American: If There Are Aliens Out There, Where Are They?


 
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