How far can we see clearly?

  • Thread starter Gold Barz
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  • #1
Gold Barz
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Is 10K reasonable?
 

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  • #2
Gold Barz
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Heres another question, can we detect radio waves clearly 1000 light years away?
 
  • #3
brewnog
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Gold Barz said:
Is 10K reasonable?


10 kilometers? I hope so! :smile:
 
  • #4
ohwilleke
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On surface of the curved earth the horizon is on the order of 40-60km (this is what they use for military planning purposes at any rate). On a clear day you can see forever (good movie, not very practical unless you have a Hubble Telescope). The Sun is more than 100 million km (100 Gm) away and you see it every day. The stars you can see with your naked eye on a clear night are in some cases hundreds of thousand or even hundreds of millions of light years away, if not further.
 
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  • #5
ohwilleke
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Gold Barz said:
Heres another question, can we detect radio waves clearly 1000 light years away?

It depends on how strong they are, but in principle, certainly.
 
  • #6
Gold Barz
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Could we detect a technological species 1000 light years away, since we havent yet...is it safe to say there are no technological species 1000 from us?
 
  • #7
russ_watters
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Gold Barz said:
Could we detect a technological species 1000 light years away
Maybe - if they were transmitting enough...
...since we havent yet...is it safe to say there are no technological species 1000 from us?
No, it isn't safe to say that: We're not looking at the entire sky with radio telescopes all the time and random broadcasts would have to be extremely powerful for us to pick up at that distance.

You are very preoccupied with this issue....
 
  • #8
plum
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Why would the broadcasts have to be powerful? They would have to be sent 1000 years ago for a civilization 1000 light years away, but radio waves generally don't become weaker as they travel through space.
 
  • #9
GOD__AM
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Gold Barz said:
Could we detect a technological species 1000 light years away, since we havent yet...is it safe to say there are no technological species 1000 from us?


I agree with Russ here. We have only been leaking/sending signals for less than 100 years. So anyone 1000 light years away still has to wait 900 years until the signals arrive. There may be other factors involved too like maybe they don't want to be detected.

plum said:
Why would the broadcasts have to be powerful? They would have to be sent 1000 years ago for a civilization 1000 light years away, but radio waves generally don't become weaker as they travel through space.

The radio waves lose intensity over distance as the photons spread out. The greater the distance the less photons you will receive.
 
  • #10
Gold Barz
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russ_watters said:
Maybe - if they were transmitting enough... No, it isn't safe to say that: We're not looking at the entire sky with radio telescopes all the time and random broadcasts would have to be extremely powerful for us to pick up at that distance.

You are very preoccupied with this issue....

Yes, very..its because on another forum, people are assuming that there are a very low number of technological species just because we havent detected anything in that 1000+ light-year sphere.
 
  • #11
plum
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If they're older than us, then they are very likely far, far older, meaning that they very likely have discovered a more efficient means of communication than radio.
 
  • #12
Pengwuino
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plum said:
If they're older than us, then they are very likely far, far older, meaning that they very likely have discovered a more efficient means of communication than radio.

Who says? Maybe there at this very moment, at the exact same technological and societal level that we are at. Plus of course, the idea that they have discovered a better means of communication makes the assumption that a better means actually exists.
 
  • #13
Pengwuino
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Gold Barz said:
Yes, very..its because on another forum, people are assuming that there are a very low number of technological species just because we havent detected anything in that 1000+ light-year sphere.

Well thats a bad basis for an assumption seeing as how the universe is like, 10839347187419273198237192873819273198231982738273124812749127481927498127418927419824 feet wide.

Hey i wonder what that jumble of numbers actually comes out to lol.
 
  • #14
Gold Barz
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Oh not the whole universe, I meant just this galaxy...the Milky Way.
 
  • #15
Pengwuino
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Oh well... still... pretty big :P
 
  • #16
saltydog
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ohwilleke said:
On surface of the curved earth the horizon is on the order of 40-60km (this is what they use for military planning purposes at any rate). On a clear day you can see forever (good movie, not very practical unless you have a Hubble Telescope). The Sun is more than 100 million km (100 Gm) away and you see it every day. The stars you can see with your naked eye on a clear night are in some cases hundreds of thousand or even hundreds of millions of light years away, if not further.

Well I do wish to be clear here. My understanding is the only stars we can see with the naked eye are those in our galaxy so that restricts us to about 100,000 light years and the only object outside our galaxy we can see with the naked eye is Andromeda which is 2 million light years away. Observational Astronomy is not my strong suite so if I'm wrong, please someone straighten me out.
 
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  • #17
ohwilleke
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I know you can see the Milky Way, which got me to 100,000. And, I know that there are galaxies you can see, which got me to a larger number.

I stand corrected on the hundreds of millions figure. This source: http://www.seds.org/messier/m/m033.html [Broken] puts the most distant at 3 million light years (M33) if your eyes are pretty normal, and 12 million light years (M81) if your eyes are exceptionally sharp. Andromeda would be the third most distant object visible to the naked eye. At least I was only off by about one order of magnitude.
 
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  • #18
Gold Barz
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So just because we havent heard anything or detected anything there still could be a technological civilization within 500-700 light years from ours?
 
  • #19
ohwilleke
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Gold Barz said:
Could we detect a technological species 1000 light years away, since we havent yet...is it safe to say there are no technological species 1000 from us?

I'll give you a fairly pedestrian counterexample.

Suppose that a technologically advanced civilization evolves on a planet we'll call Haze, which is a lot like we envisioned Venus would be before we actually got a chance to probe it -- 99%+ cloud covered, Earth like in temperature and gravity and atmosphere, and subject to frequently intense electrical storms.

First of all, astronomy might be a very late development relative to Earth, because people wouldn't even learn that there was anything other than cloud cover until they were sufficiently advanced to make rockets and high altitude aircraft (imagine Earth with no astronomy until the 1960s and there were only one or two telescopes in the entire history of the field). This would eliminate any reason to try to send radio waves into space.

Second of all, in an environment with a highly charged atmosphere, interference would be awful, especially for long range wireless applications like radio, so a civilization like this might very well have developed a purely landline based telecommunication system instead.

A civilization like that exactly contemporary with our own could exist on Alpha Centuri, just a few light years away, and we'd never know it. We don't even have the resolution to see a Venus like planet circling Alpha Centuri if there was one there. Hell, they could have a few space telescopes orbitting their planet and we'd still probably miss them if we sent at probe to Alpha Centuri and it spend a decade looking around the neighborhood. We wouldn't have any reason to know that there was life on Haze even then.

They could still be very advanced. They could have nuclear fusion power plants, a handful of small space ships that explored other planets in their system (and perhaps used a laser based communication protocol developed from the fibre optic systems used in their land lines). They could have amazing biotechnology. And, odds are that our probe would still miss them and all their artifacts and that their satellites and space ships would miss our probe.
 
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  • #20
Gold Barz
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"Second of all, in an environment with a highly charged atmosphere, interference would be awful, especially for long range wireless applications like radio."

Well I dont think thats how it is on our planet, is that even a possible planet?. I mean what are the chances of there being a civilization like that though? its like they are completely blocked from outer space.
 
  • #21
ohwilleke
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There are five planets in the solar system with atmospheres too thick to see through (Venus and the Gas Giants). There is one with partial cloud cover (Earth). There are three planets that are never cloud covered (Mercury, Mars, Pluto). If I'm a Baysian, I say that the probability of a planet being cloud covered is 61% and the probability of a terrestrial planet being cloud covered is 30%. If you gave Earth a little more cloud cover (more like Venus) and adjusted the solar flux into its atmosphere a little by adjusting its distance from the Sun, you could get the same effect without being wretchedly hot like Venus is.

We can't gauge the odds in any meaningful way because we don't have a meaningful sample size. Someday we will. Some questions don't have answers. If I roll dice in a completely dark room and don't touch them, I can't know what number I've rolled.

Also, there are all sorts of other reasons why an advanced technological society might not make widespread use of radio. Maybe the rulers on another planet granted a 100 year monopoly on radio to an incompetent businessman and so landline infrastructure took off instead. Maybe people in that civilization are very privacy conscious and don't want people to be able to use electronic intelligence. It isn't a major leap. I personally almost never use either radio or broadcast television myself. I listen to radio via the internet primarily, because my home office is in a basement and reception isn't good in the office building where I work. In the car I prefer to listen to CDs. I don't want TV at all except for DVDs, but even if I did I would do it using coaxle cable which emits very little radio inteference. I don't own a cell phone. It would take only a slight adjustment in local economic incentives for any number of reasons to make a non-radio wave broadcast technology the norm. For solar system distance communications, you'd want narrow well focused beams of photons (a laser based system, for example), to minimize fall off in signal strength with distance, rather than omnidimensional transmissions.

There are lots of good reasons not to be looking or listening as well. How much support does SETI get here? Now, suppose that you're a highly advanced civilization and that from 1500-1900 AD you engaged in a massive project to identify every large object in the vicinity of your solar system, every star and galaxy in the sky, you figured out general relativity and dark matter and dark energy and what not, and you had such perfect data after the first 100 years that for the next 100 years your computer model and your observations were a perfect match, except for a handful of supernova which you could predict statistically and determine that they (and all the other things in deep space) were harmless to you. Suppose further that this was a frightfully expensive societal project because you kept having to repair instruments hit with micrometeroids and cosmic ray bursts. In 1900 AD, don't you think that your society, perhaps slightly different in psychology from our own, might decide that running nearly perfectly accurate computer models was good enough for future reference and stop looking for anything but supernova with a sensor tuned to detecting those (which would miss weak radio waves from Earth)? You'd feel vigilant yet economically efficient.
 
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  • #22
Gold Barz
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And I agree that radio isnt the only source of communication, there might be more efficient ways of communicating that these other technological civilizations are getting by with that we dont know about.

Oh and did you read my PM to you? please reply if you can, thanks.
 
  • #23
ohwilleke
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One need only assume that a highly technological civilization might develop an environmental movement and you might not even be able to find traces in their atmosphere or much space junk.

Humans have discovered major new species of animals THIS YEAR, including whole ecosystems under the Arctic Shelf. And we've been prowling around this planet for ten thousand years since we learned how to read and write.
 
  • #24
Gold Barz
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You bring up very good points, the more advanced the civilization is the less they waste, they become more efficient.
 
  • #25
saltydog
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ohwilleke said:
I know you can see the Milky Way, which got me to 100,000. And, I know that there are galaxies you can see, which got me to a larger number.

I stand corrected on the hundreds of millions figure. This source: http://www.seds.org/messier/m/m033.html [Broken] puts the most distant at 3 million light years (M33) if your eyes are pretty normal, and 12 million light years (M81) if your eyes are exceptionally sharp. Andromeda would be the third most distant object visible to the naked eye. At least I was only off by about one order of magnitude.

Thanks for clearing that up for me. :smile:
 
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  • #26
russ_watters
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plum said:
Why would the broadcasts have to be powerful? They would have to be sent 1000 years ago for a civilization 1000 light years away, but radio waves generally don't become weaker as they travel through space.
They would lose intensity unless they wee pointed directly at us in an extremely narrow beam (ie, a radio laser). Omnidirectional radiation loses intensity in a distance squared relationship.
If they're older than us, then they are very likely far, far older, meaning that they very likely have discovered a more efficient means of communication than radio.
But we haven't, so it wouldn't help us talk to them.
 
  • #27
russ_watters
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Gold Barz said:
So just because we havent heard anything or detected anything there still could be a technological civilization within 500-700 light years from ours?
Or even 100, yes.
 
  • #28
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plum said:
Why would the broadcasts have to be powerful? They would have to be sent 1000 years ago for a civilization 1000 light years away, but radio waves generally don't become weaker as they travel through space.
On the Contrary, Electromagnetic waves of all freq. (including Radio waves) undergo Red-Shift as Space expands (however miniscule)..
 
  • #29
Chronos
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With present technology, we could easily detect radio transmissions no more powerful than those we routinely emit from almost anywhere in this galaxy. We would need only be tuned to the right frequency and pointed within about a degree of the source. The frequency thing is a little dicey, but broadcasting at the 21 cm wavelength would be a no-brainer for any advanced civilization. It would be easy to discern if a signal at that frequency was unnatural [i.e., attributable to a nonsolar intelligence].
 
  • #30
Gold Barz
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Chronos, did you read the PM that I sent you, please reply if you could...thanks.
 
  • #31
Pengwuino
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Chronos said:
The frequency thing is a little dicey, but broadcasting at the 21 cm wavelength would be a no-brainer for any advanced civilization

Whys that?
 
  • #32
GOD__AM
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Yaaks said:
On the Contrary, Electromagnetic waves of all freq. (including Radio waves) undergo Red-Shift as Space expands (however miniscule)..

There is no red shift due to expansion from our own galaxy.
 
  • #33
Chronos
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Pengwuino said:
Whys that?
21 cm is the frequency of neutral hydrogen. An advanced civilization would realize broadcasts at this frequency would have an excellent chance of being detected by other radio astronomers - who would naturally spend a lot of time mapping the distribution of neutral hydrogen.
 
  • #34
Yaaks
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GOD__AM said:
There is no red shift due to expansion from our own galaxy.
Well!!!,, i was refrerring to the Universe as a whole, Generally speaking!!...
i did not say that expanding space was the only factor influencing the red-shift phenomena..., Relative accelerating motion is also a factor (though relatively small when compared to the effects due to expanding space itself)..
 
  • #35
Chronos
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Expansion is not the only factor influencing redshift, but is the most dominant factor. There is no other viable explanation for high redshift. If redshift was intrinsic, we should see high redshift objects superimposed over low redshift objects all over the sky. But not a single, incontrovertable observation of such has been found.
 

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