SETI... the Galaxy.. radio transmissions and time and the search

[Ichingcarpenter]

See the tiny blue circle superimposed on the Milky Way? That is a sphere centered on Earth that is 200 light years across. Technologically advanced civilization on Earth would be undetectable to any observer outside of that bubble.

[tecelote]

1. How can that be said if we don't know alien technology?

[Ichingcarpenter]

2. You are right and I agree

it reeks of Anthropocentrism.

I was more intrigued by the visual of what 200 light years meant in relationship to our place in this galaxy , which is why I think that 'radio' search we do is almost meaningless to an advance ET civilization

[tecelote]

3. Yes, it certainly shows the huge possibility that other habitable planets exist and

that aliens are also a near certainty.

[Ichingcarpenter]

4. NASA estimates 1 billion ‘Earths’ in our galaxy alone

There are a billion Earths in this galaxy, roughly speaking. Not a million. A billion. We’re talking 1 billion rocky planets that are approximately the size of the Earth and are orbiting familiar-looking yellow-sunshine stars in the orbital “habitable zone” where water could be liquid at the surface.


The estimate comes from NASA scientist Natalie Batalha. Let’s go through some background information to see how she got to that number.


more
http://www.washingtonpost.com/news/speaking-of-science/wp/2015/07/24/nasa-estimates-1-billion-earths-in-our-galaxy-alone/


What that number means is mind staggering including the statistical significance and probability of ET existing at levels of technology we would think is magic.

[PJMcK]

5. The speed of light

One of the fundamentals of science is that certain physical laws are constant regardless of where an observer is located. Gravity is one of these and it's the reason New Horizons (and any other space faring vehicles) can travel on trajectories of billions of miles and arrive on target.

Another constant is the speed of light which is approximately 186,000 miles per second. In addition to photons, many things travel at that speed including gravity and radio waves. I think Ichingcarpenter is indicating that earth has been broadcasting radio signals for less than 200 years and therefore our transmissions have not traveled beyond the perimeter of the blue circle in the photograph. Accordingly, our transmissions, including television and radio broadcasts, have not yet reached any listener outside of the blue circle. Of course, the SETI scientists that are "listening" to the cosmos are searching for signals that left their broadcasters at any time during the history of the universe.

Our galaxy is really big but it's only one of the 100 billion galaxies in the observable universe. This wonderful picture effectively illustrates the awesome scale of space.

[CrispyQ]

6. Kind of a 21st Century "You Are Here" image.

Now they need to put the little blue dot on the deep field image.

[jeff47]

7. There's an even bigger problem: 1/d^2

The strength of a radio signal falls off at 1/d^2. So those radio signals 200 light years away? They aren't detectable. They are weaker than background RF.

[Jim Lane]

8. I thought SOMETHING would be detectable.

What I vaguely recall is that our artificial electromagnetic output is significant in total. An advanced species 75 light years from here might not be able to detect any specific signals well enough to try to decipher them, or to watch our sitcoms, but they'll be noticing a sudden (in astronomical terms) increase in the total emissions from one particular system. They'll see that there's no quasar or the like. They might well be able to figure out that the most plausible explanation is that an intelligent species has finally produced its Tesla and Marconi.

[jeff47]

9. Nope. Once it gets weak enough you can't tease it out from the noise.

They'll see that there's no quasar or the like

Quasars are several trillion orders of magnitude more powerful. So it takes a lot more d^2 to make it undetectable.

Unless there is something in RF that we just do not understand, we aren't detectable except in a relatively small volume of space. And we're getting quieter - moving to digital radio signals means we're putting out less power.

[BlueJazz]

10. It's possible we might not want to show where our planet resides. Not all Alien societies will be..

.. benign. I have mixed feelings about the whole search-for-life thing.