fando

Trust me, the numbers won't tell you much. We will be able to get direct images of other planets and they will be just as clear as those taken of our own outer planets through amateur telescopes. We can already resolve sunspots (starspots) on other stars. It's only a matter of time and engineering, not a matter of theoretical possibility.

Mageth

MegaDave, Fando has described a quicker, and better, solution. It would take a long time to get something even 1/1000th of the way to Alpha Centauri (about 80 years?), and that would not give us much if any of an optical advantage (increasing magnification by 1/1000th would not magically allow us to resolve planets).

Shadowy Man

A galaxy is about a billion times larger than a star. So they are easier to see from far away.

In fact, we can only resolve individual stars in some of the closest galaxies that we can see. Many, many astronomers would be very happy if we could resolve those stars in distant galaxies.

auto-da-fe

Mageth, true. I am just personlly more interested in visual confirmation of planets than the indirect ways we currently have. I think before we can attemp to find a human inhabitable planet, we are going to have to be able to visually observe it.

Back on the tangent of alien life, I have a question.

Why is it that when anyone discuss life forms, they always assume that the life form has to be carbon based, and similar to the organic life on earth? Is there some reason that our carbon based system is assumed to be the only one?

Arken

There's also a brightness factor. If you put a ball bearing next to a light bulb and look right at it from 100 yards with binoculars, you're not going to see the ball bearing because the bulb will outshine it.

Majestyk

My wholly inaccurate calculations for the lens diameters needed for extrasolar planetary resolution:

Pluto is about .08" @ 5.74 billion km.

Pluto's diameter is about 1/6 earth's

Earth would be around .146" from Pluto's perspective.

for every light year the diameter of the lens would have to be 1,900% to achieve the resolution of Earth/Pluto.

Hubble's 2.6m would need to be 4.9km for the first light year. 9,386km for the second. 17,333km for the third...

Jesse

I believe the reason is that only Carbon and Silicon can form sufficiently complex and stable macromolecules which would be necessary for life, and there are a number of reasons why silicon-based life is unlikely.

echoes

Of course we could detect their existence. However, it isn't even known if they would ever use radio, so we may be looking in vain. Maybe we are like primitive humans looking out for smoke signals as radio waves fly overhead, as the aliens use some vastly superior technology (I forgot what author came up with this analogy).

Even if they did/do use radio, we have had the technology for under 100 years. Our presence in the universe is limited to a sphere, centered at earth, of only some tens of light years. The odds of us having been detected by others seems very low.

If they, as you suggested, used radio and then abandoned it, then wouldn't there be a single hollow sphere(ring, if you prefer to think in 2D) of radio waves? It is very likely that this hollow sphere could have travelled past earth long ago, since we have been listening for a very short time.

It doesn't suprise me at all that we've found no evidence when you consider how little we have searched, and how many variables there are. Yes, it's possible that distant civilizations have had radio waves reach us since we have started listening. Are we listening in the right directions, at the right frequencies, and at the right time in history (eg, the problem mentioned in the last paragraph)?

The odds that we listen to a civilization X light years away, that used radio X years ago, at the right frequency, seems very low.

As time goes on, the probability will of course increase exponentially. As civilizations age, their spheres will expand with the volume of the sphere increasing at an acclerating rate, increasing the odds that their sphere envelopes the earth.

Friar Bellows

Nice metaphor. Time for another. Suppose we detected what was clearly an extraterrestrial signal from an intelligent source. Many (maybe most) scientists are optimistic about the chances of deciphering such a signal. But I'm not so sure. It's quite possible we would decipher something, perhaps to us something quite substantial and important, but in reality the meaning might not be anything like what the aliens intended. It would be like me travelling back in time, and handing a large collection of the finest and wisest 20th century books to a bunch of Neolithic cave dwellers, only to find them later using the books as fuel for a warm fire. They would feel as if they had made maximal use of the books, while in reality, of course, they would have completely missed the true function of the weighty tomes. I think that this sort of colossal misunderstanding between two utterly different species (alien and human) would be highly likely, and indeed, much worse than the example of the Stone Age book-burners.

contracycle

It does and it doesn't. As I recall, there are what, 1300 stars in a the sphere 50ly in radius from sol.

Markfiend wrote:
My mistake.