18 replies to this topic

[MeridianStarGazer]

Would you point the transmitter at:
A) Where you see the star?
B) Where you predict it will appear in the same number of years as its distance in light years?
C) Where you predict it will appear in twice the number of years as its distance in light years?
Or
D) A different answer (please explain)?


I'm wondering if other species sending messages know where to send it. Please tell me your way, so I can see how much disagreement there is, and guess at the likelihood the other species would know.

Edited by MeridianStarGazer, 27 March 2025 - 11:05 AM.

[Keith Rivich]

I would think any signal we transmit would be so spread out after x light years of travel it wouldn't matter exactly where its pointed.

 

I had thought experiment about building a giant mask to block the light of the sun in a pattern that would have mathematical meaning for any exo-astronomers monitoring the sky for transient phenomena.

 

Imagine if we picked up a transiting "planet" that had the first four number of Pi as its period. The mask wouldn't have to be sun sized, just big enough to knock a few percentage points off the light output.

[klangwolke]

Very cool idea, I’ve never seen that elsewhere.

[w7ay]

Imagine if we picked up a transiting "planet" that had the first four number of Pi as its period. 

What number base?  The inhabitants may not have 10 fingers :-).

 

Chen

[TOMDEY]

The closest stars --- and hope for the best.    Tom

[GalaxyPiper]

Because of time and space dialation, you would have to point ahead of the movement of the star, which would have to be figured out beforehand.

 

Forget trying to wait for a reply because of the same problem. Also, you don't know if they are ahead of behind us in technology or if there is even a technological race at all.

 

As they say, timing is everything, and so you would have to set up a repeater to repeat your message for at least a million years. So again, your message would have to be in a hardened satellite or Intersolar station that could last that long, like maybe on an asteroid, it would also have to have an A.I. to be able to repair and create parts so the best place for it would be in an asteroid field, or belt, for it to be able to smelt and create the parts.

 

While it is waiting, it might as well make other things and study the field of maybe an interstellar drive so when it does get a response, it can get their sooner vs. later.

 

And if it does not get a response, then it might as well create life so it can try again. After all, nothing lasts forever, and even omnipotent beings get tired of waiting!

Edited by GalaxyPiper, 27 March 2025 - 01:39 PM.

[bobzeq25]

We've done just a bit of this (details at the website below), the last time was about 10 years ago. The main reason we don't do it more is that people are irrationally scared that advanced aliens will come here, and for reasons I cannot fathom, harm us.

Even Stephen Hawking discouraged the idea because of this. I cannot grasp why such a smart man would be so silly.

In my view it's yet another example of absurdly overemphasizing human importance. Why would any alien race advanced enough to do faster than light travel care about us, in any way shape or form? Utterly ridiculous.

Also, if they're that advanced, they could already see random leakage of all kinds of stuff from Earth. We needn't deliberately send any more.

I'm sure they've had their fill of "Friends" reruns. <smile>

In any event, here's the history, and a good discussion.

https://en.wikipedia...iki/Active_SETI

Edited by bobzeq25, 27 March 2025 - 01:34 PM.

[GalaxyPiper]

We've done just a bit of this, the last time was about 10 years ago. The main reason we don't do it more is that people are irrationally scared that advanced aliens will come here, and for reasons I cannot fathom, harm us.

Even Stephen Hawking discouraged the idea because of this. I cannot grasp why such a smart man would be so silly.

In my view it's yet another example of absurdly overemphasizing human importance. Why would any alien race advanced enough to do faster than light travel care about us, in any way shape or form? Utterly ridiculous.

In any event, here's the history, and a good discussion.

https://en.wikipedia...iki/Active_SETI

It's better to hide behind a sand dune and study the group before just strolling down and saying "Hi".

"Flight of the Pheonix" taught us that!

Either movie...

Edited by GalaxyPiper, 27 March 2025 - 01:36 PM.

[Keith Rivich]

What number base?  The inhabitants may not have 10 fingers :-).

 

Chen

The one we know and hope the ET's with 13 fingers are smart enough to figure it out!

 

Three apples here are the same as three apples there, its just called something else.

Edited by Keith Rivich, 27 March 2025 - 01:38 PM.

[Keith Rivich]

We've done just a bit of this (details at the website below), the last time was about 10 years ago. The main reason we don't do it more is that people are irrationally scared that advanced aliens will come here, and for reasons I cannot fathom, harm us.

Even Stephen Hawking discouraged the idea because of this. I cannot grasp why such a smart man would be so silly.

In my view it's yet another example of absurdly overemphasizing human importance. Why would any alien race advanced enough to do faster than light travel care about us, in any way shape or form? Utterly ridiculous.

Also, if they're that advanced, they could already see random leakage of all kinds of stuff from Earth. We needn't deliberately send any more.

I'm sure they've had their fill of "Friends" reruns. <smile>

In any event, here's the history, and a good discussion.

https://en.wikipedia...iki/Active_SETI

To many alien invasion movies, War of the Worlds and all that. 

[GalaxyPiper]

The one we know and hope the ET's with 13 fingers are smart enough to figure it out!

Base thirteen language. Sounds ominous to me...((Shudder...))

[GalaxyPiper]

This is why speed of light communication is so limiting. Watch this video:

 

https://www.bing.com...0AE2&FORM=VIRE 

[MeridianStarGazer]

I would think any signal we transmit would be so spread out after x light years of travel it wouldn't matter exactly where its pointed.

I had thought experiment about building a giant mask to block the light of the sun in a pattern that would have mathematical meaning for any exo-astronomers monitoring the sky for transient phenomena.

Imagine if we picked up a transiting "planet" that had the first four number of Pi as its period. The mask wouldn't have to be sun sized, just big enough to knock a few percentage points off the light output.

I'd send them 1, 2, 3, 4, _, 1, 2, 3, 4. No way that is natural. Big curved mirror on Mercury. Only need to tilt it a hair to go dark. Ideally bright enough to be notice by pre-technological society and get recorded in verbal stories.

But they might interpret it to mean the God's demand a sacrifice.

[MeridianStarGazer]

We've done just a bit of this (details at the website below), the last time was about 10 years ago. The main reason we don't do it more is that people are irrationally scared that advanced aliens will come here, and for reasons I cannot fathom, harm us.

Even Stephen Hawking discouraged the idea because of this. I cannot grasp why such a smart man would be so silly.

In my view it's yet another example of absurdly overemphasizing human importance. Why would any alien race advanced enough to do faster than light travel care about us, in any way shape or form? Utterly ridiculous.

Also, if they're that advanced, they could already see random leakage of all kinds of stuff from Earth. We needn't deliberately send any more.

I'm sure they've had their fill of "Friends" reruns. <smile>

In any event, here's the history, and a good discussion.

https://en.wikipedia...iki/Active_SETI

I'm certain our TV signals disappear into the background noise of the Sun, even with a huge ear. Only powerful directed signals could be heard.

It is possible that weapons and technology can't advance past a certain point, and that it might be wise to wait another 50 years for ours to plateau before we reach out to others. But I highly doubt aliens will attack us for send them some music. They already know from the pollution in our atmosphere that we are here.

Anyone want to say where specifically you would aim to get a message to people on a star? One person said just send a wide spread. I think a directed one is needed to be heard.

[w7ay]

I'm certain our TV signals disappear into the background noise of the Sun, even with a huge ear. Only powerful directed signals could be heard.
 

That's definitely very true.  But in the old days, you can also use a very narrowband filter around the carrier of the TV signal (the good old analog TV signals even have three of them, the RF carrier, the video carrier and the audio carrier).  Those signals are still floating away from us out in space.   You will need a very narrowband receiver, but the carriers, by FCC riules, were very stable.

 

The carrier of the current digital TV standard is much weaker.

 

There have even been very narrowband SETI efforts that use bandwidths that are so narrow that we had to de-doppler the earth's rotation in the direction the dish is pointed at.  Like this search by Paul Horowitz:

 

https://www.scienced...019103586901296

 

(Yes, that Chen in the author list is me; I am really just in the author list because Paul was using my lab at Stanford when he was on sabbatical from Harvard, and I kept harrasing him about different things :-).  Back then, I was developing some hardware for the NASA SETI project (see Appendix B here:  Speaking of that NASA report, Jill Tarter in that paper is the one the main actress in the movie "Contact" is patterned after (Carl Sagan did not come up with that person out of his imagination :-), and the blind astronomer in the movie is the D. Kent Cullers in the report.  The B.M.Oliver in the report was Barney Oliver, and if memory serves, he had not yet retired from his day job as V.P of Research at HP (and headed HP Labs). 

 

A funny anecdote:  Paul Horowitz visited Stanford before deciding to take his one year sabbatical to make sure that is where he wanted to spend a year (heck, the weather alone should decide that!).  When he revealed his plan of using ultra narrow bandwidths when I "interviewed" him (pretty much the same reason we use etalons for solar Hα pictures), my first question to him was "what about interstellar dispersion, which would broaden any carrier?"  Paul said he hadn't considered that.  On his way home, he visited Yosemite.  On his hike up the Yosemite Falls, he took one piece of paper and a pencil with him.  While up there, starting just with the charge of an electron (talk about starting with first principles :-), he derived how much a 1.4 GHz signal would get dispersed by, and concluded that his premises were still OK :-).  He did fill both sides of the paper with tiny writing.  So, yeah, not only is there signal attenuation to the TV signals, there is dispersion too.

 

Chen

Edited by w7ay, 27 March 2025 - 04:31 PM.

[Sky King]

I would point it anywhere. But I wouldn't send a weak, slow signal. I would communicate with something "they" already should know about. It will take something new to reach this goal.

 

We are soon to have LISA. LISA is a space-based gravitational wave detector constructed of three spacecraft separated by millions of miles.

 

"...These three spacecraft relay laser beams back and forth between the different spacecraft and the signals are combined to search for gravitational wave signatures that come from distortions of spacetime... NASA is a partner in the European Space Agency (ESA) led mission, which is scheduled to launch in the mid-2030s and we are getting ready for it now!"

 

LISA is a giant receiver. Turn it around and make LARRY, a giant gravitational wave transmitter. When we can transmit using some variant of gravitational waves, that would be a serious signal. 

 

Impossible? That's likely what was said prior to September 14, 2015. "The first direct detection of gravitational waves, a prediction of Einstein's theory of general relativity, occurred on September 14, 2015, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected a signal from the collision of two black holes." 

Edited by Sky King, 28 March 2025 - 11:27 AM.

[bobzeq25]

I'm certain our TV signals disappear into the background noise of the Sun, even with a huge ear. Only powerful directed signals could be heard.

It is possible that weapons and technology can't advance past a certain point, and that it might be wise to wait another 50 years for ours to plateau before we reach out to others. But I highly doubt aliens will attack us for send them some music. They already know from the pollution in our atmosphere that we are here.

Anyone want to say where specifically you would aim to get a message to people on a star? One person said just send a wide spread. I think a directed one is needed to be heard.

1. You can't travel faster than light. To people with technology that could do that, picking out our leaked signal would be trivial. But beyond boring.

2. The angular width of a solar system at that distance is beyond tiny. No way could be direct a signal with that precision.

Feeble human brains simply can't contemplate what an advanced society would be like or the size of the universe. They underestimate those by orders of magnitude. <smile>

Edited by bobzeq25, 27 March 2025 - 08:16 PM.

[MeridianStarGazer]

I've not done the calculation, but I wonder how the practical limits of concentrating a singnal compare to the number of arc seconds a star travels in several years.

Diffraction makes it spread out, and is related to aperture. I don't know if diffraction affects signal quality.

Would using the frequency of hydrogen mean there is a lot of background hydrogen noise? I read that microwaves at 1-10mhz is best.

[w7ay]

I've not done the calculation, but I wonder how the practical limits of concentrating a singnal compare to the number of arc seconds a star travels in several years.

Diffraction makes it spread out, and is related to aperture. I don't know if diffraction affects signal quality.

Would using the frequency of hydrogen mean there is a lot of background hydrogen noise? I read that microwaves at 1-10mhz is best.

The problem is that even the largest steerable radio telescope is only about 100 meters diameter.  1.42 GHz is about 21cm (actually nicknamed 21cm line by radioastronomers), so in terms of wavelength, the dish is less than 500 wavelengths -- the half power beamwidth is about 12 arc minutes.  "Diffraction" (wave nature) causes sidelobes that are identical to what we see in Airy rings.  Not a huge problem for transmitting power loss, but a bigger problem for receiving, since the sidelobes at the feed antenna picks up noise from the warm ground (compared to the detectors, which are cooled to near absolute 0 K), but you can control that by designing a feed antenna that does not illuminate the ground, at a small loss to aperture.  

 

Although the sky coverage is more limited, the Arecibo (Puerto Rico) antenna was much larger, but that radiotelescope is no more -- in spite of that, lots of SETI search was done at Arecibo, both by piggy backing on other experiments, or alone.  The first SETI attempt was done by Frank Drake (Project Ozma) with just a 26m dish :-).

 

The usual reason for picking the microwave region near 1.4 GHz is that for earthbound telescopes, it has the best SNR.  The "romantic" reason, attributed to Barney Oliver, is that it is at the "water hole" region -- Hydrogen spin flip radiation is at 1420.404 MHz, and there are four lines that are associated with Hydroxyl radical (OH) around 1667 MHz -- ergo H2O :-).

 

https://www.seti.net...e/waterhole.php  for example, shows the water hole inside the best SNR region between 1000 MHz and 10000 MHz.

 

And other rationales include that is a natural place to transmit if the transmitter and the receiver are trying to meet up blindy.  But I have also read of searches at 2x Hydrogen spin flip, to avoid the background noise from H.  I heard of suggestions at pi times Hydrogen, but I am not sure anyone actually did it :-).

 

I think the 1.420 GHz Hydrogen spin flip was either predicted or discovered during or just after WWII.  It was not until the early 1960s that the Hydroxyl radical lines were observed by Sandy Weinreb, using the autocorrelation receiver that he created for his Ph.D thesis.  (Sandy was my supervisor when I was a summer intern during my Junior and Senior years at Green Bank in the late 1960s :-).

 

Chen

Edited by w7ay, 28 March 2025 - 02:33 AM.