There are many galaxies in the universe. Is there any other Earth-like planet out there?
Ok, it is easy to say yes but the basic idea is statistics. There are more and more planets discovered outside of our solar system virtually every day. With better instruments, ever smaller planets can be discovered. Besides, it depends on your definition of 'earth-like'. If you restrict this to size, the distance to its star (with respect to the 'habitable zone') and an potential atmosphere (thus ignoring the questions of atmosphere chemistry and life), it is a rather clear yes.
News (all referring to a discovery published December 2011):
- NASA Kepler-mission news - The Kepler-20 system
"NASA's Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system."
- Nature News - Kepler discovers first Earth sized exoplanet
"Whizzing around the star Kepler-20, about 290 parsecs (946 light years) from Earth, is not only an Earth-sized planet, but also something just a touch smaller — a Venus."
- NYTimes - NASA's Kepler spacecraft discovers 2 Earth-size planets
"[...] astronomers from NASA’s Kepler spacecraft announced Tuesday that they had discovered a pair of planets the size of Earth orbiting a distant star."
- Gautier, T.N., Charbonneau, D., Rowe, J.F., Marcy, G.W., Isaacson, H., Torres, G., Fressin, F., Rogers, L.A., Désert, J.-., Buchhave, L.A., Latham, D.W., Quinn, S.N., Ciardi, D.R., Fabrycky, D.C., Ford, E.B., Gilliland, R.L., Walkowicz, L.M., Bryson, S.T., Cochran, W.D., Endl, M., Fischer, D.A., Howell, S.B., Horch, E.P., Barclay, T., Batalha, N., Borucki, W.J., Christiansen, J.L., Geary, J.C., Henze, C.E., Holman, M.J., Ibrahim, K., Jenkins, J.M., Kinemuchi, K., Koch, D.G., Lissauer, J.J., Sanderfer, D.T., Sasselov, D.D., Seager, S., Silverio, K., Smith, J.C., Still, M., Stumpe, M.C., Tenenbaum, P. & Van Cleve, J. 2012, "Kepler-20: A sun-like star with three sub-neptune exoplanets and two earth-size candidates", Astrophysical Journal, vol. 749, no. 1. (free access)
The answer is strongly defined by how one defines "Earth Like."
The working definition has yet to be established for the scientific purposes that I've seen.
The common minimum: terrestrial, within the liquid water zone, and not more than about 4 Earth masses; a lower bound of about 1/2000th Earth mass (large enough to be self rounding). In which case, there's one about 1 light second away... Luna.
Over a dozen extrasolar worlds fit that very broad definition.
Let us narrow it to worlds which have an atmosphere; this sets the mass to between 2 Earth masses and 1/4 Earth mass. There are several detected in the same range, but all are over Earth mass, and as far as I know, outside the Goldilocks zone. Gliese 581 has 3 candidate worlds (581 c, 581 d, and 581 e) that are within the correct mass and potentially have atmospheres. Kepler-452b is 1.6 earth diameters, and in the ecosphere of it's parent star; its atmosphere isn't yet detected.
If we narrow it further, to free atmospheric oxygen on such a world, only one so far is known, and we are on it. Until the Terrestrial Planet Finder mission (presuming it isn't cancelled before then; as of Jul 2015, it's indefinitely postponed), it's unlikely to be detected, as the current instruments are not optimized for that.
We are in eternal pursuit of a solution to a vast equation on the likelihood of life elsewhere in the universe. With the extremophiles that we have found here on Earth, it is extremely unlikely that life itself is missing or even rare out there. That presumed, the next question is about intelligence. The factor that seems most important for us is the geological history of Earth with the various extinctions timed such that successor forms of life become dominant. It is certainly possible that at least the dinosaurs could have evolved to significant intelligence and sufficient manipulation capability to make and use tools. The timing of extinction events and the ecosystems of the intervals certainly could determine the overall outcome. With basic intelligence achieved, can intelligence and concomitant technology occur with sufficient speed for the intelligent species to survive a major extinction event and move on to a level detectible across space to us. There are so many ways for intelligence to wipe itself out or to be destroyed by external factors.
Without building truly massive long base line instruments, we may never know except by random chance. That is a very unsatisfying answer, but I fear that it is the only one that we shall ever have. Every day, I awake with the hope that I am wrong.
It's July 2015. NASA Claims that they have discovered Earth 2.0 , Approx 1400 Light years.