That is a good question! People are trying to find signals of life. But, you have to realize that signals can only travel as fast as the speed of light in a vacuum. No planets around stars that are habitable, like ours, have been found yet in our galaxy. The next nearest galaxy (Andromeda) is about 2 MILLION light years away. That means that the light we see from Andromeda is 2 million years old when it gets to us, so we are seeing it now as it looked 2 million years ago.

If people evolved somewhere in the Andromeda galaxy, another huge spiral galaxy like ours, and their civilization was about a solid as ours, then they may possibly have sent out signals 20 to 50 years ago, like us; no more. So we would not be able to receive their signal until 2 million years after it was sent out.

The universe, we believe, is about 14 billion years old. The oldest galaxies formed when the universe was about 1 billion years old. Our sun formed about 5 billion years ago. The oldest light-emitting objects we can see are about 13 billion years old - but if there were civilizations like ours in any of those galaxies, we won't know about it for 13 billion years ...and that does not even account for the expansion of the universe.

Sorry... we may never contact another civilization.

If you are interested in this stuff, I suggest you read The Physics of Star Trek, by Lawrence Krauss. He explains it all quite well.

Good question. There are several reasons:

1. We would not expect to have found life with the exploration that we have done, even if it were there. We can observe planets around other stars mainly by means of their gravity. These planets are for the most part the size of Jupiter or larger, and are much closer to their stars than our Jupiter. We would not expect to find life on a Jupiter-like planet, and Earth-sized planets are still too small for us to detect (yet).

2. We have thus far found no evidence of sentient life that is trying to find us just as we are trying to find it. This may be because planets with sentient life only have it for a fairly short period of time(the Earth has been around for 4.6 billion years, and we have only been detectable to the universe for the last hundred). We may have missed each other in time.

All of this said, the fact that we have not found life yet in other solar systems and have not detected extraterrestrial intelligence indicates that the universe is not as teeming with life, at least sentient life, as some would like to believe. Still,there could be life elsewhere in the local group of stars (~20 light year radius), and that we have not found it yet, and would not have found it even with our current technology.

It is interesting how we are able to gather information and discover new galaxies, planets and solar systems. What is very hard about this is that we can use tools to sense the existence of these things but we don't yet have capability to go too much farther beyond our own planet. Now, don't get me wrong... being able to tell what the atmosphere of Pluto is made of which is somewhere 2.9 to 4.6 billion miles away from the sun (compared to the 93 million miles away from the sun that Earth is), but getting pictures of Pluto was very hard... even the Hubble, one of the best telescopes was able to pick up only a few details.

So finding a way in through the atmospheres to know if life really does exist is more than difficult. Another reason that scientists do not believe there is other life is because on Earth all life is carbon based and relies on oxygen for existing. Other planets in our solar system have hardly any if any oxygen in their atmospheres. So we are pretty sure that if there is life out there it wouldn't be much like ours, and we are unsure of what to expect if there is. We also rely heavily on the sun and on water. Planets closer to the sun are very hot and planets much farther from the sun are very cold. This would make life as we know it difficult.

Also, the first four planets are the terrestrial (have land) ones in our solar system and the rest are gas giants. It's hard to imagine what life would be like in a big ball of gas without any land. There are some speculations that bacteria once grew on Mars and maybe still do but these are pretty recent findings somuch more research on this is needed.