Other civilizations will explore the universe for live at the speed of light (as we do).
Any civilization within 3.8 billion light years with a large enough telescope knows of life here! Some might say the telescope would have to be size of their host planet, EXACTLY! Look up interferometry.
Spectroscopy is what we use to determine (quite easily) the compounds in the atmospheres of extraterrestrial bodies: the 7 other planets, the sun, and by 2020 large extra-solar planets 3-4 times the size of Jupiter that are close to us.
For about the last 3.8 billion years give or take.2 billion years, bacteria and other primitive organisms have been creating oxygen. Light from the sun is reflected through our atmosphere, obscuring certain wavelengths of light. The light reflected from the earth with the first traces of elevated oxygen is now 3.8 billion light years from earth. Commonly accepted estimates for the size of the universe are about 11 billion light years. So almost half of universe has the ability to know of our existence! A sphere with a radius of 3.8 billion light years is enormous!
An extremely low estimate of the abundance of life in the universe (one civilization per galaxy) would equate to about 30-50 billion civilizations that fall within the spherical detection zone with a radius of 3.8 BLY.
Civilizations within 100 light years can tell we have gone through an industrial revolution by light wavelengths obscured by CO2.
Physical probes??!! Pfffffft.
Slashdot Mirror
Other civilizations will explore the universe for live at the speed of light (as we do). Any civilization within 3.8 billion light years with a large enough telescope knows of life here! Some might say the telescope would have to be size of their host planet, EXACTLY! Look up interferometry. Spectroscopy is what we use to determine (quite easily) the compounds in the atmospheres of extraterrestrial bodies: the 7 other planets, the sun, and by 2020 large extra-solar planets 3-4 times the size of Jupiter that are close to us. For about the last 3.8 billion years give or take .2 billion years, bacteria and other primitive organisms have been creating oxygen. Light from the sun is reflected through our atmosphere, obscuring certain wavelengths of light. The light reflected from the earth with the first traces of elevated oxygen is now 3.8 billion light years from earth. Commonly accepted estimates for the size of the universe are about 11 billion light years. So almost half of universe has the ability to know of our existence! A sphere with a radius of 3.8 billion light years is enormous!
An extremely low estimate of the abundance of life in the universe (one civilization per galaxy) would equate to about 30-50 billion civilizations that fall within the spherical detection zone with a radius of 3.8 BLY.
Civilizations within 100 light years can tell we have gone through an industrial revolution by light wavelengths obscured by CO2.
Physical probes??!! Pfffffft.