The 20th century was incredibly rich in scientific discoveries. Within that century more people worked in science and more money was spent on science than in all of the preceding human history. Among the great discoveries of the past century are the following (make your own list before reading on, and add the names associated with the discoveries):
Albert Einstein- His ideas changed the course of modern physics and astronomy. (From: Library of Congress)
Mass and energy are the same thing
Gravity is a deformation of space
Time and matter come in minimum quantities
The Milky Way is our galaxy seen edge-on
There are billions of other galaxies out there
Most of them are billions of light years away
The universe is expanding
The Sun is powered by fusion of hydrogen to helium
Elements are made inside stars, some during normal fusion, some when the star explodes
The Earth is 4.6 billion years old
Basic organic molecules are easily made from inorganic stuff
Life is more than 3.8 billion years old
Life is incredibly diverse, especially at the microbe level
Slime molds, trees, and people have much the same genetic material
The evolution of complex life forms is strongly influenced by mass extinctions
In addition to such discoveries (many of which obviously bear on the likelihood of Life in the Universe; as you can easily verify, please) there are equally impressive feats of engineering accomplishments. Here are some of these:
Fast and efficient automobiles
Air travel, from propeller-driven planes to jet planes
Submarines
Rocket Propulsion
Nuclear fission (power generators and bombs)
Nuclear fusion (bombs only, so far)
An array of highly sophisticated drugs
Electric household devices, from refrigerators to microwave ovens
Telephone, radio, TV
Computers and computer programming
Two achievements stand out:
Scientific: The galaxies around us, even though separated by millions of light years, seem to have much the same types of stars as our own, and appear to follow the same rules of physics and chemistry. Thus, whatever we learn about physics and chemistry in our labs on Earth and in our local solar system and our local galaxy appears applicable to the universe as a whole. (If this were not so, we could not speculate at all about conditions for life elsewhere.)
Technical: We actually made it to the Moon and back. The people who landed there brought back samples, demonstrating beyond a shadow of doubt that the Moon is just another planet of sorts, with rocks not unlike the most common rocks on Earth. This feat, in fact, is the first time that earth-bound life invaded another celestial body, by design (rather than by being splattered about through impact). The design came from a highly evolved many-celled eucaryotic organism with a big brain. But by far most of the organisms landing on the Moon (millions) were micro-organisms on the skin and within the guts of the lunar explorers. As far as our bacteria are concerned, we humans are a good way to get around, like a ship well-stocked with supplies.
Eventually, the ships that bacteria built over geologic time and that provide a sheltered environment and mobility, might seed other planets with bacteria to prepare them for more extensive occupation at a later stage. For example, it is possible that certain types of bacteria could survive right now on one of the moons of Jupiter (Europa). We could, in principle, decide that we wish to make sure there is Life on that body - or every body in the solar system that is able to support life of a kind evolved on Earth. This is a more likely scenario than moving some of the most complex organisms (ourselves) into rather inhospitable environments. Of course, we do not usually think of bacteria as "us." However, there are good reasons why we should. As far as we can tell, all living things on Earth are closely related, by common ancestry. This is the chief reason they have no problem feeding on one another - each can use the other's building materials.
