No ET! Ever?

[Anomalocaris]

Hence unless we blanket the sky with signals, it would be very tough for us to send any short pulse signals in such a way that it would arrive at the same place and time as the target.

As I pointed out earlier, the Wow signal may have been such an interstellar beacon:

Other hypotheses include a rotating lighthouse-like source, a signal sweeping in frequency, or a one-time burst.

https://en.wikipedia.org/wiki/Wow!_signa...27s_origin

Again, in a radio transmission, one is faced with either a directional antenna (such as AM radio) or an omnidirectional transmission (such as FM).  The Sun is omnidirectional, but per Einstein's famous E = m * c^2, there is no way that we or anyone else in the Universe will ever be able to generate the equivalent energy of 10,000,000 nuclear bombs per second.  And, so, a directional transmission is the best bet, but the more narrow the transmission (such as a laser), the near certain result is scattering and/or defection of the beam while it propagates the tremendous distances of interstellar space, and given the 300 or so billion stars in the Galaxy, where does one point the beam to?  In addition, someone on the receiving end has to be listening, and we, as a species, are simply not doing that.  The Ohio State Big Ear telescope is now a golf course!

And, so, the conclusion that ET is nowhere to be found because ET does not exist is at least premature.

With our current technology it is possible to generate a controlled laser pulse lasting 10e-18 seconds.   It is not far beyond our current technology to give such a pulse an instantaneous power output greater than that of the sun, which is about 10e26 watts.   But because the pulse is so short, the total energy output of such a 10e26 watts laser pulse lasting 10e-18 seconds is still quite modest, about the magnitude of a month's energy output from typical rooftop solar panel installations on some big box stores like Walmart or Home Depot.

So it is actually not prohibitively difficult to broadcast an omnidirectional light signal strong enough to be easily detectable within a few dozen light years by a civilization comparable to ours that's looking for a short duration pulse light signal.

[Jehanne]

With our current technology it is possible to generate a controlled laser pulse lasting 10e-18 seconds.   It is not far beyond our current technology to give such a pulse an instantaneous power output greater than that of the sun, which is about 10e26 watts. 

A watt is a joule per second, and so, talking about a power output less than one second is meaningless, even if the "math" works out.  Again, it is physically impossible to detect a 10e-18 burst of anything across interstellar space, or, for that matter, outside of laboratory conditions.  The best that fiber optic cables can do is on the order of picoseconds (1 out a million million or 10e-12).  Even "short" GRBs last on the order of 2 seconds.

[Anomalocaris]

Power doesn't require complete seconds.   There is nothing sacred about one second.  We talk about and work with power of event that occur on duration vastly shorter than one second all the time.   The power of a bomb, for example.  The shortest duration of fast gamma ray bursts probably have more to do with physical dimension of the region in which the gamma ray burst event occurs.  It's hard to get an radiation event to occur over less than 2 seconds if the transmitting mechanism, like an accretion disk around a black hole, spans 2 light seconds. The transmitting mechanism of communication transmitter can be just a few millimeters or centimeters across.

There is no reason I can see why detecting ultra short pulses over open broadcast is physically impossible.  Perhaps the technology to do so hasn't been refined yet for really short bursts.  But given the degree to which we've improved our observational techniques and  sensitivity over the last 25 years when motivated by the search of exoplanets, it seems dangerous to even assume such technology as detecting 10e-18 second pulses over open broadcast can't be perfected in just 2-5 years years should the funding for the effort becomes available.   Granted visible light pulses will stretch out and lose peak intensity due to interstellar scattering.  But that effect ought to be small within a few light years.

[Jehanne]

Power doesn't require complete seconds.   There is nothing sacred about one second.  We talk about and work with power of event that occur on duration vastly shorter than one second all the time.   The power of a bomb, for example.  The shortest duration of fast gamma ray bursts probably have more to do with physical dimension of the region in which the gamma ray burst event occurs.  It's hard to get an radiation event to occur over less than 2 seconds if the transmitting mechanism, like an accretion disk around a black hole, spans 2 light seconds.  The transmitting mechanism of communication transmitter can be just a few millimeters or centimeters across.

There is no reason I can see why detecting ultra short pulses over open broadcast is physically impossible.  Perhaps the technology to do so hasn't been refined yet for really short bursts.  But given the degree to which we've improved our observational techniques and  sensitivity over the last 25 years when motivated by the search of exoplanets, it seems dangerous to even assume such technology as detecting 10e-18 second pulses over open broadcast can't be perfected in just 2-5 years years should the funding for the effort becomes available.   Granted visible light pulses will stretch out and lose peak intensity due to interstellar scattering.  But that effect ought to be small within a few light years.

It may be better to express things simply in joules.  Fact is that stars are basically point sources which is why they, unlike planets, twinkle on clear nights (planets, unlike stars, have angular size on the night sky); this fact, called scintillation, is going to impact any source of light, and so, assuming that you could produce a narrow, coherent form of laser light and aim such perfectly, it is virtually certain that such will get scattered somewhere in the interstellar medium.

[Anomalocaris]

Power doesn't require complete seconds.   There is nothing sacred about one second.  We talk about and work with power of event that occur on duration vastly shorter than one second all the time.   The power of a bomb, for example.  The shortest duration of fast gamma ray bursts probably have more to do with physical dimension of the region in which the gamma ray burst event occurs.  It's hard to get an radiation event to occur over less than 2 seconds if the transmitting mechanism, like an accretion disk around a black hole, spans 2 light seconds.  The transmitting mechanism of communication transmitter can be just a few millimeters or centimeters across.

There is no reason I can see why detecting ultra short pulses over open broadcast is physically impossible.  Perhaps the technology to do so hasn't been refined yet for really short bursts.  But given the degree to which we've improved our observational techniques and  sensitivity over the last 25 years when motivated by the search of exoplanets, it seems dangerous to even assume such technology as detecting 10e-18 second pulses over open broadcast can't be perfected in just 2-5 years years should the funding for the effort becomes available.   Granted visible light pulses will stretch out and lose peak intensity due to interstellar scattering.  But that effect ought to be small within a few light years.

It may be better to express things simply in joules.  Fact is that stars are basically point sources which is why they, unlike planets, twinkle on clear nights (planets, unlike stars, have angular size on the night sky); this fact, called scintillation, is going to impact any source of light, and so, assuming that you could produce a narrow, coherent form of laser light and aim such perfectly, it is virtually certain that such will get scattered somewhere in the interstellar medium.

The visible twinkling comes from the atmosphere.  Point sources don't twinkle when viewed outside the atmosphere.  There is scattering by interstellar medium.  But around the vicinity of earth significant scattering takes >>50 light years worth of interstellar medium. We can actually measure the amount of scattering by distance by measuring exoplanet transits.

[Gawdzilla Sama]

Power doesn't require complete seconds.   

It may be better to express things simply in joules.  

Or Pirate-Ninjas.

[Jehanne]

It may be better to express things simply in joules.  Fact is that stars are basically point sources which is why they, unlike planets, twinkle on clear nights (planets, unlike stars, have angular size on the night sky); this fact, called scintillation, is going to impact any source of light, and so, assuming that you could produce a narrow, coherent form of laser light and aim such perfectly, it is virtually certain that such will get scattered somewhere in the interstellar medium.

The visible twinkling comes from the atmosphere.  Point sources don't twinkle when viewed outside the atmosphere.  There is scattering by interstellar medium.  But around the vicinity of earth significant scattering takes >>50 light years worth of interstellar medium.  We can actually measure the amount of scattering by distance by measuring exoplanet transits.

You're absolutely correct, however, we are talking about stars and planets, the diameters of which are many magnitudes greater than some sort of radio transmitter, which means that a narrow band signal, such as laser, would be still subject to scattering in the interstellar medium.  Stars are, of course, much more powerful than are interstellar laser beacons, and being omnidirectional, the scattering that they experience is much less.  However, their light still does get scattered:

https://en.wikipedia.org/wiki/Lyman-alpha_forest

Once again, I think that the "Wow! signal" may have been authentic:

https://en.wikipedia.org/wiki/Wow!_signal

But, if was authentic, it was, at the Wiki article states, likely some beacon that was sweeping the (alien) sky in more or less random directions.

What I am railing against here is what was stated in the BBC link in the OP, that is, that "absence of evidence" is grounds for concluding evidence of absence; hence, given the laws of Nature, it is completely understandable why we have not heard from ET or why ET has not visited our solar system.  Other than a powerful, sweeping beacon, the challenges, in my opinion, for direct radio communication are likely either impossible, or at least practically infeasible.  The only evidence that we are likely to get for ET will be indirect evidence, the type that came in the Wow! signal, or perhaps, KIC 8462852:

https://en.wikipedia.org/wiki/KIC_8462852


In short, the BBC article is just plain wrong.

[Mr Greene]

That picture you show reflects the precession of equinox.   It has nothing to do with earth's motion or proper motions of target stars and therefore does nothing to increase the difficulties of targeted transmission.

Your original claim was, "the stars are in pretty much the same positions as when they were observed by the Greeks / Ancient Chinese." (emphasis mine).

In any case, the proper motion of the Sun around the center of the Galaxy (at nearly 700 times the speed of sound), would be sufficient to cause a narrow band radio transmission to miss the Earth, not to mention the Earth's motion around the Sun (around 60 times the speed of sound).

The wobble on the Earth's axis is an irrelevance, and calculating deflection could be done by fighter pilots in combat so hardly an insurmountable problem.
In any case unless you were targeting a specific star for some unspecified reason a general area would suffice.

[Anomalocaris]

Your original claim was, "the stars are in pretty much the same positions as when they were observed by the Greeks / Ancient Chinese." (emphasis mine).

In any case, the proper motion of the Sun around the center of the Galaxy (at nearly 700 times the speed of sound), would be sufficient to cause a narrow band radio transmission to miss the Earth, not to mention the Earth's motion around the Sun (around 60 times the speed of sound).

The wobble on the Earth's axis is an irrelevance, and calculating deflection could be done by fighter pilots in combat so hardly an insurmountable problem.
In any case unless you were targeting a specific star for some unspecified reason a general area would suffice.

Fighter pilots have radar to give them range to target.  We have nothing comparable to measure range to stars. In any case the range measurement error tolerance acceptable for fighter combat is much greater than that acceptable to making a narrow pulse signal intercept a star.  This is because in aerial combat, the dimensions of the target aircraft and the dimensions of the bullets are both vastly greater relative to range to target than the dimension of the target star and the dimension of the pulse signal relative to range to the star.

Blanketing an area can solve that problem, but it also greatly reduce the strength of signal reaching each detector in the area, and this magnifies the probability that the signal would be overlooked.

[Jehanne]

Your original claim was, "the stars are in pretty much the same positions as when they were observed by the Greeks / Ancient Chinese." (emphasis mine).

In any case, the proper motion of the Sun around the center of the Galaxy (at nearly 700 times the speed of sound), would be sufficient to cause a narrow band radio transmission to miss the Earth, not to mention the Earth's motion around the Sun (around 60 times the speed of sound).

The wobble on the Earth's axis is an irrelevance, and calculating deflection could be done by fighter pilots in combat so hardly an insurmountable problem.
In any case unless you were targeting a specific star for some unspecified reason a general area would suffice.

We're talking Mach 690 or so, not to mention the fact that ET's system is also in motion by a similar amount, but on a different vector, which will only compound the problem.  Also, don't forget that laser light is still subject to the inverse law:

https://www.quora.com/Is-the-light-from-...ht-sources

And, so, once again, ET's transmitter is going to have to be at least in the billions (or, trillions) of watts in order to get a sustained signal, and, we are going to have to be looking for such a signal at the right time and the right spot in the sky.  And, this is something that we are not doing, at least at present.