PDA

View Full Version : Space/SETI enthusiasts, need your help!



Hannibal7
10-25-2012, 11:14 PM
I am writing a screenplay, in which a signal from another civilisation enters the solar system. The signal is tracked by one person on Earth to a destination point on Mars. The personís job is to map asteroid orbits and identify target asteroids for mining etc. But on the side he searches for ET signals, using work equipment and such.


The bit Iím having trouble with, is what form the signal will take and how as scientifically, and yet as visually exciting, as possible will this person stumble across it. Ideally I would like him to witness the signal/beam move closer in real time.


I had in mind a beam (perhaps laser/photon), with sentience, so that it actively seeks out its destination on Mars. But I have no idea how to detect this, would a laser beam be visually observable in space? What other marker would it leave?


Perhaps a neutrino beam, but from what I know, it would be near impossible to detect especially when you were not actively looking for it.


Radio waves seem too primitive to use, the source is around 13,000 light years away. I donít want the method to exceed the speed of light. Maybe a combination; a laser beam wrapped around radio waves to give it concentration and direction, but allow it to be easily detectable by our technology.

Thanks for any help, any general thoughts on the subject would be greatly appreciated (perhaps other works to draw inspiration from). Iíve looked at the film/book Contact, my story is a bit different in that the detection of the signal has to be done secretly and with limited resources, due to the totalitarian environment that is established.

Drachen Jager
10-26-2012, 12:42 AM
I'm not sure exactly what you're looking for. No, a laser on Mars would have to be ridiculous for an Earth-based amateur to spot it. What's wrong with Radio?

Also, current consensus among physicists is that FTL might not be impossible after all. I don't know if that helps you.

Any non-FTL signal must have been travelling for over 13,000 years, though I suppose you've already thought of that.

Hannibal7
10-26-2012, 02:05 PM
I thought radio would be too primitve for an advanced race to use, and over that distance it would have dispersed too much. Ideally I would want a concentrated beam that could find a specific target.

Is it right that if the source of the signal (transmitter) is removed then the signal would carry on into space regardless?

Thanks

spottedgeckgo
10-26-2012, 02:48 PM
radio waves are no different than light waves in structure, only in frequency, they are both EM. If an advanced culture had a target to transmit to, then a focused beam could be made with radio waves, in theory, but it isn't going to be visually appealing. Neither is a laser beam.

If you want visually appealing, I would go probe. A small probe (travelling 13k light years) can accelerate to near the speed of light, coast for 13k years, but as it approaches it's target (Mars) it will have to slow down.

The propulsion on a probe can be as visually appealing as you need. Giant solar sail that acts like a parachute, nuclear explosion, jets, weird purple alien beam, whatever you like. You could even see it changing course, etc.

I believe SpaceX is working on an asteroid mining project scheduled to start analysing "near earth objects" by 2016. I might be wrong on the company name but they could provide you some insights as to the tech that you would hunt asteroids with. Their focus now is optics, and I think their plans are to use a type of satellite drone to fly close to the asteroid to get a closer look.

Hope this is helpful.

RichardGarfinkle
10-26-2012, 03:00 PM
I'm not sure exactly what you're looking for. No, a laser on Mars would have to be ridiculous for an Earth-based amateur to spot it. What's wrong with Radio?

Also, current consensus among physicists is that FTL might not be impossible after all. I don't know if that helps you.

Any non-FTL signal must have been travelling for over 13,000 years, though I suppose you've already thought of that.

Might not be impossible in this case means there are models wherein it can happen. But there is no evidence that any of those models is true.

In writing SF FTL / no FTL is one of those thinigs one should decide early on in the work since it fundamentally defines aspects of the universe.

As to the original question. Any signal travelling 13,000 light years is going to undergo serious degradation. Space is empty but not as empty as you might think. Every particle out there can interact with and therefore degrade the quality of your signal. You can encode information redundantly but for a trip that long you would have serious problems getting anything through.

Also hitting a target as small as a planet (let alone a point on a planet) when your targeting information is 13,000 years old and therefore your shot when it hits will have 26,000 years of multibody gravitational affects, meteor impacts, geological changes, atmospheric problems, etc, etc makes for a dubious system.

In terms of what kind of beam to use, there are particles that interact a lot (like electrons) and essentially have no chance of crossing that distance with a signal intact. Particles that interact a fair amount (like photons) which have the problems mentioned above and particles that interact rarely (like neutrinos) which might be able to make the journey, but creating a receiver would be next to imossible. Neutrino detectors catch a few events daily if they're lucky and that's from swarms of trillions of neutrinos.

If you need no FTL, do you also need 13,000 LY? Much shorter distances would make your journey more plausible.

Hannibal7
10-26-2012, 04:07 PM
Thanks for the info, I don't understand the 26,000 year comment. It will take the signal 13,000 years to reach its target, there is no reply to the signal. It was sent as a one way message.

Unfortunately, the distance does have to be that many light years, it is part of the story. A neutrino beam could be justified in that the 'catcher'/receiver would also be alien so it can just be put down to their advanced technology, but the human on earth would still need to be able to detect it. Do you know if you have to catch neutrinos to detect them or do they give off any other hints they are?

I think I'm going to have to do the same in 2001: A Space Odyssey, when the monolith sends out its signal, Arthur C Clarke just writes how detectors recorded an unknown energy source streaking across the solar system, leaving behind a radioactive trail. A lot simpler!

Marta
10-26-2012, 09:11 PM
Detect the beam moving closer? It would not be detectable until the light (or radio source, whatever part of the electromagnetic spectrum you opt to use; they all travel at the same speed) arrives. So there's no way to know a beam has been started until the light is received. If you want to show that the source of the light is moving, that's different. If it's fast enough, you could use a Doppler shift.

As for a target being Mars, with Mars rotating around the sun and the light traveling for 13,000 years, how in the world is this beam going to predict exactly where the planet will be that far in advance?

Hannibal7
10-27-2012, 12:18 AM
Yes I realise that I'm going to have to do all the detection post event now, which is a shame because it would be more stimulating in real time.

The story involves a signal travelling 13,000 light years, and finding a point on Mars. I just have to come up with a solution of how, on my own, or with help from others. When alien technology is involved and the genre is science fiction the possibilities are countless.

Perhaps the beam of energy holds intelligence, it travels from tachyon to tachyon, conscious of its destination. I'm not going to use this it's not good enough, but it's a start.

RichardGarfinkle
10-27-2012, 12:21 AM
Thanks for the info, I don't understand the 26,000 year comment. It will take the signal 13,000 years to reach its target, there is no reply to the signal. It was sent as a one way message.

Unfortunately, the distance does have to be that many light years, it is part of the story. A neutrino beam could be justified in that the 'catcher'/receiver would also be alien so it can just be put down to their advanced technology, but the human on earth would still need to be able to detect it. Do you know if you have to catch neutrinos to detect them or do they give off any other hints they are?

I think I'm going to have to do the same in 2001: A Space Odyssey, when the monolith sends out its signal, Arthur C Clarke just writes how detectors recorded an unknown energy source streaking across the solar system, leaving behind a radioactive trail. A lot simpler!

Sorry, the 26,000 years refers to the time between the freshness of targeting information and the time when the beam arrives. If the target is 13,000 LY away then your information is 13,000 years old when you decide to send the signal, and the signal arrives 26,000 years after the information used to calibrate it was emitted.

spottedgeckgo
10-27-2012, 01:48 AM
Agree with Rich. He's just saying that if you are 13kly away, then you are calibrating your targeting off of data that's already 13 years old. Then the beam takes another 13000 years to arrive.

I think probes are perfect for what you are trying to do, but sounds like you don't want to go that route. (There is the issue of the probe navigating the Oort cloud without smashing into a rock, but I've yet to see Sci-fi that worried about that problem). Probes can also update their target info as they go so adjustments can be made internally if it starts to drift off course. Okay, I'm done trying to mess up your story now. :)

I wish you the best. I would refrain from neutrinos myself, just because neutrino communication (if useful by alien tech in deep space) is till going to be catching a ton of static from the sun.

Hannibal7
10-27-2012, 02:12 AM
Thanks, I will think about probes, it may be the way to go. Perhaps to add a sci-fi spin, the probe/s could be nanobots/nanoprobes, tiny little things. Maybe the nanoprobes are riding on a wave/beam, which are directed by the technology of the probe. Just thinking on my feet here. Is that even remotely possible (in a sci-fi context); nanobot technology infused with electrons/photons etc!!

benbradley
10-27-2012, 02:44 AM
Okay, these are advanced aliens sending this signal, but aiming a beam from 13,000 light years away to hit one planet in the Solar System would require astronomical (all puns intended) accuracy. What's more likely is a hugely powerful laser is used and is aimed at the Sun. At a distance of 13,000 light years it will fan out to, let's say, the size of the Solar System (and even then that's some amazingly good collimation).

Someone on Earth who just happens to be aiming a large telescope (which might be on Earth or in orbit) at the source would see an unknown light source of a specific color (most point sources of light in the sky aren't THAT colorful, and even those that are are a mix of several wavelengths), prompting a spectrogram to be done with the light. It would be VERY suspicious when it come back monocromatic (a single wavelength of light). This would indicate a laser, which would either be a VERY unusual natural occurrence, or a sign of an intelligence sending a message.

But there's no way to know if the laser signal is intended for a single planet. The modulation (changes in light brightness or wavelength that would carry a message) could be detected, but it would take at best months or years to decode, learn the language, and figure out what it was saying or where it was directed (insert alien language for ROT13: "Guvf fvtany vf vagraqrq bayl sbe gur sbhegu cynarg sebz guvf fgne, nyy bguref cyrnfr qvfertneq").

Thanks for the info, I don't understand the 26,000 year comment. It will take the signal 13,000 years to reach its target, there is no reply to the signal. It was sent as a one way message.

Unfortunately, the distance does have to be that many light years, it is part of the story. A neutrino beam could be justified in that the 'catcher'/receiver would also be alien so it can just be put down to their advanced technology, but the human on earth would still need to be able to detect it. Do you know if you have to catch neutrinos to detect them or do they give off any other hints they are?
Yes you have to catch them. There are neutrino detectors on Earth, but the tend to be huge and underground, and it would be harder to tell where they come from, much less where they're aimed at.

Agree with Rich. He's just saying that if you are 13kly away, then you are calibrating your targeting off of data that's already 13 years old. Then the beam takes another 13000 years to arrive.
What they're saying is for the beam to hit Mars, the people pointing the beam have to aim it at where Mars will be 13,000 years in their future, but also they're seeing it as it was 13,000 years in their past, so they have to predict its location 26,000 years in the future from the point they see it at. It makes the precision aiming even that much harder, much less being able to see Mars from that far away.

BDSEmpire
10-27-2012, 07:09 PM
Unfortunately, the distance does have to be that many light years, it is part of the story. A neutrino beam could be justified in that the 'catcher'/receiver would also be alien so it can just be put down to their advanced technology, but the human on earth would still need to be able to detect it. Do you know if you have to catch neutrinos to detect them or do they give off any other hints they are?


Neutrinos are weird particles. They're barely "here" in this universe to begin with. They don't interact with much and the interactions tend to be incredibly weak. I suppose it would make an okay particle for alien hand-waving tech that is setup to emit and detect them because of their exotic nature.

http://www.sno.phy.queensu.ca/images/man_on_deck.GIF

Check that out, it's the Sudbury Neutrino Observatory. It's a globe sitting 2km underground filled with heavy water (deuterium-enriched water). Several times a day a neutrino goes whipping through there and slams into a particle. This slows it down from the speed of light and WHAM there's a flash of light and a shock cone as this poor particle comes back to interact with our universe. The photon detectors in the big bubble then pick up those flashes and backtrace the shockwave to determine how big/from where the neutrino came.

This is a HUGE globe of water and it still can barely slow down a few neutrinos a day. OH, a more useful thing to know - there's approximately 65 billion neutrinos passing through every square centimeter of Earth facing perpendicular to the sun. Chew on that for a bit - the Sun is *spewing* out neutrinos as a result of its business of being a nuclear furnace and these things just don't interact.

Using them as a messaging medium is probably unlikely but that's the fun of speculative tech, aliens can do anything!

StormChord
10-31-2012, 02:58 AM
Look up the "Wow!" signal. That should give you some idea of how that kind of signal would appear on the readout.