Sending light through space

[tklerck]

How much energy would it take to send a decent amount of light to one of our nearest star systems to a specific point (i.e. planet)? If it's possible could we send morse code type signals across space to other worlds?

 

[odysseus145]

I don't really know how much energy is involved, but the lasers used to measure the distance to the moon are several kilometers wide by the time they reach it, and when the get back to the earth, detectors only get a single photon every few seconds.<br /><br />Here is a link detailing the Apollo Laser Ranging Experiments <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>How much energy would it take to send a decent amount of light to one of our nearest star systems to a specific point (i.e. planet)? If it's possible could we send morse code type signals across space to other worlds?<p><hr /></p></p></blockquote><br /><br />It depends on what you mean by "decent amount". But the simple answer is that it would take a lot. But yes, if it's possible, you could send signals with it. It could be morse code, or binary-encoded ASCII text, or pretty much any code.<br /><br />Right now, the cheapest way to send information using electromagnetic radiation is in much longer wavelengths than visible light. Radio waves are the best for that. But like the lasers used to measure the distance to the moon, they spread out as they travel, which means that not only is the beam quite wide by the time it reaches the target, it is also very diffuse and harder to detect. The signal from Pioneer 10 recently became too faint to be detected even by the Arecibo Telescope, despite it being emitted as a very tight beam, and despite nearly all of the probe's power being diverted to the transmitter. It also seems that Pioneer 10 was having a hard time receiving signals from Earth; in the end it would only respond if given an active signal from the world's most powerful radio transmitter -- located also at Arecibo.<br /><br />Deliberate signals containing information have been sent to possible life-bearing stars using the Arecibo Telescope, as part of the SETI project. It's questionable whether the signals are strong enough to be detected by technology comparable to our own, but you never know what technology any possible aliens might have. So far, there has not been an answer, but it would take a number of years for the signal to get there anyway. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[worthj1970]

I have a very basic quesiton along these lines. I know that Optical doesn't always equal Visible. However, when we take a telescope and look at something far away we see it more or less as it is, right? So (and forgive my ignorance) why can't we transmit in some way light that is more or less intact as it travels through space?

 

[CalliArcale]

You are correct -- when we look through a telescope, we see an object more-or-less as it is. However, many objects aren't particularily visible that way. For instance, the glorious structure of many nebulas is only visible in long exposures. The human eye doesn't build up an image in the same way as a piece of photographic film does when exposed for, say, three minutes. (It <i>does</i> build up an image, but not in the same way, or in as much detail or clarity.)<br /><br />We can transmit light like that. It will stay intact. It will appear fainter the farther away the observer is from the light source, just like stars do, so you need to either make it brighter or have a better receiver on the other end. It is definintely quite possible, theoretically.<br /><br />By the way, amateur astronomers sometimes refer to telescopes as "light buckets". This is because the primary function of a telescope is not magnification (contrary to popular belief). Your eyepiece will magnify the image, but the telescope will allow you to get considerably more light into your eye from a particular object than you would get if you just looked at it with your naked eye. That will improve the resolution, which will make the magnification far more useful. The bigger the telescope, the more light it gathers, and the finer its resolution. The finer the resolution, the more you can usefully magnify the image. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[spayss]

"...why can't we transmit in some way light that is more or less intact as it travels through space?"<br /><br /> Think how much energy is being used!!! We are looking at stars and collections of stars. <br />

 

[Maddad]

Sending a message to another star is an inefficient method of communication. Yes, we do bounce radar beams off nearby planets such as Mars, but the nearest star, Proxima Centauri, is 750,000 times further away than Mars is at its closest. Because of the inverse square law, that faint signal we get back from Mars would be 500 billion times weaker after going to Proxima Centauri.<br /><br />Send a physical object to the system with a map of where we are so they know where the probe came from. It's not as sexy as a high zoot cell phone call, but it could work.

 

[newtonian]

maddad- Good post and good math.<br /><br />Not to make light of the matter, but a light object would be easier (take less energy) to send!<br /><br />Bright idea! Heavy subject!<br /><br />Of course, that only works if you have a specific target. Like a specific earth-like planet for example.<br /><br /> Otherwise the broad, potentially spherical, sending out of an electromagnetic message would be more likely to reach the unknown target. <br /><br />Like a pulsar, but with non-periodic informational coding!<br /><br />I doubt we have a PRAYER of sending a message that way to extraterrestrial intelligence. Our power is so limited compared with a pulsar, or compared with....<br /><br />However, note my capital idea!

 

[tom_hobbes]

Nice to see you around again! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font size="2" color="#339966"> I wish I could remember<br /> But my selective memory<br /> Won't let me</font><font size="2" color="#99cc00"> </font><font size="3" color="#339966"><font size="2">- </font></font><font size="1" color="#339966">Mark Oliver Everett</font></p><p> </p> </div>

 

[newtonian]

eburacum45- Well, I didn't actually forget that. Of course, you are correct about fosused lasers if you have a target.<br /><br />Do you suggest a target?<br /><br />Before agreeing on the energy comparison, you would have to convince me with some actual numbers.<br /><br />Other posters on this thread indicated we cannot focus well over long distances. <br /><br />Meanwhile, I kind of agree with maddad but am open minded.

 

[Maddad]

Newtonian<br />"<font color="yellow">Of course, that only works if you have a specific target. Like a specific earth-like planet for example.</font><br />It also works if you send a bazillion probes.

 

[silylene old]

If you wanted to send a signal to a <i>really distant</i> location, nothing beats a light signal...provided you boost it with gravitational lensing! Aim a focussed laser beam at a properly aligned mini-black hole and it would be detectable many galaxies away. I challenge that it would be much more improbable to send a message-spacecraft that far. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[newtonian]

silylene - On the spin thread, I referenced the 1998 Britannica Science volume concerning the atom laser. That would be another option.

 

[Maddad]

You might send a signal to a nearby star either by radiation or by a probe, but you may be underestimating the vast distances involved with a signal to a galaxy that far away. How are you going to communicate with someone when you have to wait a quarter of a billion years for a response from them?<br /><br />http://www.maddad.org/astronomy/distance01.htm<br />A few days ago I put up a web page discribing those distances.