Lets Talk About Things Science Cannot Explain

[Cathbad]

Something else science can't explain: Why, if I lay one wire/cord on top of another, ten minutes later, they are totally entwined/tangled!!

I blame gremlins.

~brooding~

 

[BAYLOR]

Something else science can't explain: Why, if I lay one wire/cord on top of another, ten minutes later, they are totally entwined/tangled!!

I blame gremlins.

~brooding~

That's because the wires are secretly plotting against you.

 

[Cathbad]

That's because the wires are secretly plotting against you.

I KNEW it!!!

 

[Ray McCarthy]

signal washout?

No idea what that is.
Inverse Square law, possible transmitter power, dish sizes, background cosmic and star noise.
Shannon's law (1948) identified the limits for any communication.

Some basic graphs about radio communication I've collected over the years

1) Shannon Limit

Basically every time you double the distance on a radio system that only just works very slowly you need four times the power.
You need more power the more data you want to transmit per second.
The fixed parameters most limiting are the channel noise and distance.
Eventually your aerial /dishes uses half your planet and transmitter the entire energy the planet has. Any realistic Civilisation has much less power and a much smaller aerial/dishes than that.

2) Background noise versus Radio frequency (ground level)

3) Attenuation of signal at ground level
Much easier to do giant dish arrays on the ground than in space

It's a complicated subject. Basically there are practical limits as to how far you can send an artificial signal. Power and dish size.
The limits for reception are background noise and dish size. We can essentially make receivers quieter than any background noise quite easily, so receiver technology hasn't been a problem for maybe 20 years.

Telescopes and radio telescopes work better in space. One big system of each on the far side of the moon would be good for half the month as at least the moon would shield from our man-made interference and atmospheric attenuation. When the far side is facing the sun, isn't much good!

Any interesting places are very far away.

Any aliens would have to be EXACTLY pointing their giant high power transmitters and dishes at our dishes pointing exactly at them, AND the link would have to be within the Shannon Limit.

Not likely.
Our sun isn't especially powerful, it's power is about 386 billion billion mega Watts
386,000,000,000,000,000,000 MW
When you hear about a 1 MW TV transmitter, that's ERP, the effect of aerial gain. The real power might be 200kW.
But let's say we had 100 of the giant Chinese 500m dishes (Arecibo is 2nd largest at about 320m I think) and had a 1000 MW transmitter on each. That's still 1/3,860,000,000,000,000,000 th of the sun's power!
The 100 giant dishes is a gain of about 5,000,000,000 so total ERP at 100% efficieny (unlikely) is still about 1,000,000,000 times less than the sun.
We are not about to build a receiver with 100 dishes that size.
Who would build the transmitter?
Remember it has to be pointed EXACTLY at us.
We have to notice.
if 20 Light Years away, then if we build a transmitter to reply that is 40 years later the aliens hear the signal. They have to be STILL pointing at us!
With that power you have to alternate listening and transmitting, not a big problem.

With Radio it takes massive resources for lifetimes for EACH potential target. Takes two to Tango.

With Spectroscopic analysis you use a moderate size dish (mirror). The James Webb Space Telescope has a single 6.9m mirror (equivalent exactly to dish on radio telescope). You are using maybe a 1000,000,000,000,000,000,000 MW transmitter (the remote star) modulated by the atmosphere of the planet of interest. You'll know in maybe a year if it's likely got life and even industry. You can then feel "not alone". You could send a probe (maybe take 100s of years or 1000s years to get there). Building a giant transmitter is unlikely idea as it's likely they will be too far away and why would they be pointing a giant array of dishes at us to hear us?

Anyway, that's why radio based SETI is probably pointless.

 

[BAYLOR]

I had no idea it was that complicated , wow.

 

[Cathbad]

I had no idea it was that complicated , wow.

he do put da facts in!

 

[BAYLOR]

he do put da facts in!

He really does know his stuff.

 

[Ray McCarthy]

was that complicated

It's not really complicated.
It's like walkie talkies*. (CB, FRS, or whatever). Doing 200m (200 yards in America) is easy. Doing 2km is hard to impossible in a city, easy on a pair of hills, doing 200Km is really hard and involves bouncing signal off the Ionosphere.

Space is REALLY big. Talking to Voyagers and New Horisons is really really hard. They haven't even got out of the hallway yet!
Milky way is maybe 180,000 LY across.
Nearest stars are 4.5 to 10 LY.
Best guess is that "life" could easily be 100 LY away minimum.
We can maybe reliably communicate about 0.1 LY, today (35 light days). New Horizons and the Voyagers are much closer!

My SF has real science in it. The Aliens in my stories only use radio and laser links up to about 16 Light Days distance. They monitor radio transmissions of new worlds from about that distance in their starships (don't ask me how the starship works for Interstellar distances, if I knew that I'd be working in ESA or NASA or RosCosmos!)

[* I can explain why Police /ambulance/taxi mobile radio works better and why cell phones work often at 1/10th power of a walkie talkie, but that's a subject for another thread]

 

[Ray McCarthy]

Another thought ...
You can see the cosmic noise and terrestrial and solar noise are all worse at lower frequencies on the graphs above.
Redshift
A blueish star moving away from us fast enough (very far away) will have that blue light shifted to radio frequencies. That and background noise from "big bang" and all the radio noise for all the visible stars is what some aspects of the cosmic noise is. The observable radio limit of the universe is much larger than optical size (maybe due to Red Shift), but eventually the red shift of the star's signal is into the background noise. Hence even should we fill the entire far side of the moon with radio telescopes, there is still a limit to the observable universe due to "cosmic noise".

 

[Stephen Palmer]

Forum posts with graphs!
Respect is due Ray.

 

[Ray McCarthy]

posts with graphs

Really old ones prior to Excel etc!
Shannon / Nyquist's work in 1948 was originally called Shannon's Theory, but actually the whole thing about definition of communication, how far it can go, the percentage of errors and the speed of it, all relating to channel size, channel noise, speed and transmission power turns out to be based PURELY on the laws of Thermodynamics, it's that fundamental and basic. So there are no magic recipes, no technology waiting to be discovered (the communication medium and modulations etc can't solve the issues, we can work to a few percent of the Shannon Limit today).

So in recognition of the totally definitive mathematics and the underpinning of Thermodynamics, it's called Shannon's Law now. The Shannon limit is the region beyond 100% channel efficiency, no communication at all is possible in that greyed out region of the complex graph. The various points are examples of where various real world systems existed maybe 20 years ago.

Most Mobile Internet speed claims and claims for MIMO, new techniques for more speed or range (you can have one at the expense of the other) are misleading or out right lies, or only apply a few metres apart in a noise free lab.
So called "White Space" or other claims of spectrum sharing are lies. Share spectrum and the noise/interference increases, errors rise, TV pictures may pixellate or freeze, data connections or voice calls drop etc.

 

[Stephen Palmer]

I remember doing Shannon's Law at university... many years ago...

 

[Parson]

@Vertigo and @Ray McCarthy ---- Thanks so much for clearing that up for me. It does beg the question that if this was so well known in mid-1900's or before how on earth did radio SETI get started? Didn't the scientists know that this project was doomed before they started?

 

[Cathbad]

Didn't the scientists know that this project was doomed before they started?

.Hope springs eternal.

 

[Ray McCarthy]

mid-1900's or before how on earth did radio SETI get started? Didn't the scientists know that this project was doomed before they started?

I think SF is the reason*.
It's an unwarranted belief in the the Karashev Scale, which likely has no basis in reality, it's purely speculation.
(Nothing to do with Aliens in DS9, or those scantily clad women that are famous for being famous).
A Karashev Type II Civilisation, "A civilization capable of harnessing the energy radiated by its own star", is supposed to be able to build a powerful enough transmitter or "modulate" a star with a simple signal. We could pick that up.
Except there is zero evidence that a civilisation can be as advanced as that, or would want to make a Niven ring (easier) or Dyson sphere, or that such structures are even possible (no known materials are strong enough), or want to build massive transmitters or modulate a star and why would they advertise their existence?

As I and others have said, SETI is a reasonable idea using spectroscopic analysis, SETI using radio reception (or worse transmitting a signal) may turn up interesting natural signals. There is no reason, even if there are 10,000 technologically advanced civilisations in our galaxy, all wasting a vast amount of energy on beacons that we could receive any of it, even if their dishes were pointed at us. The power would be too low and distance too great. Also why would they expend such resources building 100s or 1000s of dishes and transmitters and waste all the power simply to advertise their existence?

[* It's also the reason for a lot stupid gadgets where the real plan isn't making money selling you the Internet connected coffee maker, but reselling your personal information and selling subscriptions]

 

[Ray McCarthy]

Didn't the scientists know that this project was doomed before they started?

a) How many of the scientists or SETI organisers consulted or listened to Communications Engineers? Scientists are specialised.
b) How many SETI radio enthusiasts are scientists and how many are employees?
c) How many dishs are actually 100% dedicated to SETI or are really doing radio astronomy, with the the recorded signals merely being analysed by SETI enthusiasts off site? See SETI at Home.
d) All of the SETI Radio organisation stuff seems to be one small university group.
e) How many SETI radio scientists have a day job and are just "interested" and supportive, because "why not".

If I was doing Radio Astronomy as the day job I'd certainly keep a look out. For a start, all of the supposed alien signals definitely found have turned out to be extremely interesting natural phenomena.

It seems the current SETI Radio project is based in Berkeley Space Science Lab, it's using only a copy of data received by Arecibo for other purposes and basically has almost no funding.

possible evidence of radio transmissions from extraterrestrial intelligence using observational data from the Arecibo radio telescope. The data are taken "piggyback" or "passively" while the telescope is used for other scientific programs. The data are digitized, stored, and sent to

SETI radio is mostly harmless, I don't think it's using up much Radio astronomy resources. The real SETI work is already spectroscopic observations by scientists trained to understand the signals captured.

 

[Ray McCarthy]

Something science doesn't understand:
Fast Radio Bursts
There are weird bursts of energy coming from deep space

However we didn't understand Pulsars (light and radio bursts) for a long time. We already can use them to navigate in the Solar system and if we had starships we can use them as a "Galactic Navigation System", even the degree of mapping we have to today would be good enough if we had "jump drive" type starships tomorrow.

 

[Mirannan]

A couple of points:

First of all, I disagree with our radio output not being detectable. The issue is that our output is in a number of sharply defined wavebands, and this means less competition in those wavebands from Sol. Also, there are peculiar things about it such as being pulsed, modulated and polarised.

In addition, Sol is not particularly powerful. I seem to have read somewhere (can't find the reference) that in certain wavebands Earth actually emits more power than Sol.

 

[Vertigo]

A couple of points:

First of all, I disagree with our radio output not being detectable. The issue is that our output is in a number of sharply defined wavebands, and this means less competition in those wavebands from Sol. Also, there are peculiar things about it such as being pulsed, modulated and polarised.

In addition, Sol is not particularly powerful. I seem to have read somewhere (can't find the reference) that in certain wavebands Earth actually emits more power than Sol.

Interference from the sun is only one aspect, the inverse square law is by far the bigger influence on the range of our radio signals and there's just no getting away from that.

 

[Ray McCarthy]

I disagree with our radio output not being detectable.

Only up to a few light years at best, it's basic physics. It doesn't matter HOW good the dishes and receivers are on a 100 LY away planet, it's impossible.
It was my day job to do these sorts of sums.

I seem to have read somewhere (can't find the reference) that in certain wavebands Earth actually emits more power than Sol.

No. Look at the graphs.

Note that only higher frequencies are any use at all over any distance. The lower frequencies where most of the power used to be (AM Radio) are completely useless. TV transmissions are the only significant band for space, they are quite directional and now lower power and the "better" higher frequencies replaced by mobile. Mobile phone bases are a cell based system with very directional aerials, about 10,000th of power of TV.

AM Radio is 0.06MHz to 26MHz, very little above 14MHz and hardly anything under 0.5MHz. Very many transmitters have closed, more than half. Completely swamped by Cosmic noise even at our nearest neighbour.
FM Radio is 64MHz to 108MHz depending on country, More directional aerials to save power. This might be detected at a few LY, but it's dubious due to directional nature. Longer distances swamped by cosmic noise.
DAB is about 175MHz to 220MHz, not much of it, more directional and lower power. Few countries have it.
Band I TV is gone (40MHz to 60MHz band)
Band III TV is gone (175 MHZ to 275 MHZ)
Other transmissions in 26MHz to 450MHz; such as CB, Aircraft, Marine, Amateur/Ham, FRS, mobile radio, security etc are all very low power less than 1/1000th of TV.
UHF TV used to be 470MHz up to 870MHz, Now only up to 600, 700 or 790MHz depending on country and lower power and more directional.

Satellite TV is very low power, about 10,000th of UHF TV and very directional. Only the uplinks can be received in space (3GHz, 11GHz and 20GHz bands approximately). The power is too low to be above cosmic noise even 4LY away as the destination satellites are only 22,500 miles away.

Radar is terrestrial and very directional. Admittedly it's a very high peak power (very narrow pulses), but very little signal reaches space. Again basic physics and cosmic noise, never mind solar noise means that even at 5LY (approx the nearest star) would be dubious.

There is nothing else.
A hypothetical starship with a very large array of dishes between the Kuiper Belt and Oort cloud could monitor a lot, but not aliens on another star. A probe at that distance would only receive signals specifically aimed using our big tracking radio telescopes