Exist the Extraterrestrial Life, do you think about? The Universe is finite or infinite?

Question

WHICH IS THE PRINCIPAL THREAT FOR THE HUMANITY?

Answer 1

Scientists have long speculated about the possibility extraterrestrial life.
Planned searches for life involve examining the spectra of Earth-like planets.
Searches for intelligent life involve scanning the sky for artificial radio signals.

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(1) Scientists have long speculated about the possibility of extraterrestrial life.
Early in the history of astronomy, there were two views on life in the universe:
(1) The universe is finite, and the Earth is unique - the only place in the universe suitable for life. (This was the view of Ptolemy, for instance, with his finite, Earth-centered universe.)
(2) The universe is infinite, and contains innumerable inhabited worlds. (This was the view of the ``atomist'' philosophers of ancient Greece, such as Democritus, Epicurus, and Metrodoros of Chios.)
It is highly likely, in my humble opinion, that life exists elsewhere in the universe. Just consider the numbers:

about 100 billion galaxies in the universe
about 100 billion stars per galaxy
THEREFORE, about 10 billion trillion stars in the visible universe
If only one star in a trillion has inhabited planets, that's still 10 billion worlds with life. (However, they would be spread very widely apart.)

Life on Earth is based on complex carbon compounds (proteins, fats, starches, DNA, you name it) suspended in liquid water. Although science fiction writers have speculated about silicon-based life and even more exotic lifeforms, I'll concentrate on the search for life as we know it - carbon-based life dependent on the existence of liquid water. A key question (and one that remains unanswered) is whether life forms very readily on planets with liquid water, or whether it's an extremely rare accident. If life existed on other planets in our Solar System, it would support the hypothesis that life forms readily.

Although liquid water once flowed on Mars, the only evidence that life ever existed on Mars are some structures in a Martian meteorite that have been identified as tiny fossils. (For more information about life on Mars, you can read the lecture notes I prepared on this topic for my Astronomy 161 class.) A dark horse in the ``life in the Solar Systems'' race is Europa, one of the Galilean moons of Jupiter. Europa seems to have an ocean of liquid water beneath its icy surface. It would be interesting to drill through the ice and see what lies beneath...


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(2) Planned searches for life involve measuring the spectra of Earth-like planets.
Where should we look if we wanted to find life (as we know it) outside the Solar System? First of all, we can forget the short-lived O and B stars on the main sequence. Once the Earth cooled enough for liquid water to exist on its surface, it took about 400 million years longer for life to arise. Any star with a lifetime of less than a few hundred million years probably won't have life on its surrounding planets. Second, we can forget the dim, cool M stars on the main sequence. In order to be warm enough for liquid water to exist, any planets around an M star would have to be in a very small region very close to the star.
In looking for Earth-like planets (terrestrial planets with oceans and life), it's best to look around Sun-like stars. So far, planets around other stars have only been found indirectly, by their gravitational effect on the parent star. (For more information about planet hunting, you can read the lecture notes I prepared on this topic for my Astronomy 161 class.) This method only finds massive, Jupiter-like planets; low-mass, Earth-like planets have a much tinier gravitational effect.

Potentially, it is possible to take direct images of Earth-like planets. To do this, it helps to look at infrared light. Sun-like stars have a surface temperature of 6000 Kelvin; thus, their spectrum peaks at visible wavelengths. Earth-like planets, however, have a surface temperature of 300 Kelvin (about 80 Fahrenheit); thus, their spectrum peaks at infrared wavelengths. It also helps, when you are searching for Earth-like planets, to have high resolution. From 10 parsecs away, the Earth and Sun would be separated by a maximum angle of only 0.1 arcseconds.

A proposed space-based telescope, designed to look for Earth-like planets, is the Terrestrial Planet Finder. The TPF will not only take snapshots of planets around other stars, it will measure their spectra, looking for absorption lines of ozone (O3), carbon dioxide (CO2), and water (H2O) at infrared wavelengths. The Earth has lots of ozone and little carbon dioxide compared to sterile terrestrial planets like Mars and Venus. (Don't hold your breath; the Terrestrial Planet Finder is currently scheduled for launch in the year 2012.)

(3) Searches for intelligent life involve scanning the sky for artificial radio signals.
For purposes of discussion, I will define ``intelligent life'' as consisting of beings that have sufficiently advanced technology to send a spacecraft or a message between stars. (By this definition, human beings just barely qualify as intelligent.) Even if life is common in the universe, intelligent life may be rare. It took 400 million years for life to evolve on Earth, but 4 billion years for (just barely) intelligent life.
If intelligent extraterrestrial life exists, why hasn't it visited Earth recently? Actually, when posed this way, the question sounds pretty egotistical. You might equally well ask the question, ``What's so great about our planet that would cause aliens to flock to it?'' Nevertheless, an insatiably curious and extremely thorough alien civilization might decide to visit all the stars of the galaxy in turn, eventually visiting the Sun in the course of their survey.

Interstellar travel requires either (A) lots of time, or (B) lots of energy.


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(A) The slow route between stars.
The spacecraft Voyager 1 and Voyager 2 are leaving the Solar System, after completing their surveys of the Jovian planets. Currently, they're traveling at about 25 km/second (pretty fast by Earthbound standards: about 50,000 mph). However, if either of the Voyagers were pointed at Proxima Centauri, it would take them 50,000 years to get there.


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(B) The fast (but expensive) route between stars.
For spaceships traveling near the speed of light, the length of the journey (as measured on the home planet) is little longer than the light travel time. In addition, the relativistic effect of Time Dilation makes the trip even shorter for observers aboard the spacecraft. The drawback: travel at speeds close to the speed of light requires vast quantities of energy. In doing a bit of research for this lecture, I unearthed an amusing factoid: At current energy costs, accelerating one human being to 20% of light speed costs $2 billion dollars.

Travel at speeds close to that of light is not economically and technically feasible at humanity's current technological level. An extremely advanced civilization (one which is able to harness the entire energy output of a star, for instance) might be able to do it? What would bring such highly advanced beings to Earth? We can only speculate.

Travel is expensive; talk is cheap. That is, sending material objects between stars requires the investment of large amounts of energy; sending messages using electromagnetic radiation requires a much smaller amount of energy. If we wanted to send a message to a civilization orbiting a distant star, what wavelength would we use? Microwaves seem to be the best choice. The sun is not a tremendously powerful source at microwave wavelengths, so there's little danger of our message from Earth getting lost in the Sun's glare. Wavelengths longer than 30 centimeters are impractical because there's too much background `noise' from emission by interstellar gas. Wavelengths shorter than 3 centimeters are impractical because they are absorbed by water vapor and oxygen in the Earth's atmosphere.

In fact, we have been (inadvertently) beaming radio messages into space for three-quarters of a century, since large-scale commercial radio broadcasts first began in the 1920's. An expanding sphere of FM and TV broadcasts surrounds the Earth. (They become increasingly faint with distance, however, so it's not likely that other civilizations are intently watching the original broadcasts of ``I Love Lucy''.) If we ever succeed in detecting radio waves from an alien civilization, it will probably be the result of the civilization deliberately broadcasting a very strong signal into outer space saying ``WE ARE HERE! WE ARE HERE!''

Search for Extraterrestial Intelligence (SETI) programs are currently ongoing (although Congress cancelled a NASA-sponsored SETI program as a cost-saving measure). Privately funded SETI searches are using telescopes that range from small amateur radio telescopes to the huge Arecibo radio telescope. Nothing so far...

Answer 2

Hiya

Yes, the probabilities of there being other planets that support life are high, based on the sheer volume of planets and even applying the smallest mathematical probability, there would be many millions of planets that could support life.

The universe is infinite in a sense, but only if you consider the fact the it creates it's own space as it expands , not that it expands 'into' pre existing space. That is a hard theoretical concept for us to grasp, but is the reality. So it expands into itself, but is of infinite size.

The greatest threat to humanity is humanity itself, wanton destruction of the planets resources, wholesale global warming and deforestation of the rain forests etc. Our generation has got away with it, others won't it's too little too late. If this is not correct then blame the abnormal solar flares from the sun, which some scientists think is the real culprit.

Either way though it looks pretty lose / lose long term!!

Answer 3

General Relativity says the universe could be finite but without an end, like the surface of a sphere. General Relativity so far is consistent with tests and observations.

I believe there are other life forms out there, we can't be the only beings in such a huge universe.

Like everybody else said, we are humanity's number one threat.

Answer 4

Other life exists out there somewhere. It's just so extremely far away that we will only see them if they come here. There is more than one type of alien life, too. You can bet on that.
The universe is infinite and endless. It does not expand or contract. It is the biggest thing that can ever exist. It is made of nothing, but in that vast nothingness, floats everything known and a lot of unknowns. It wasn't created and will never end. It has and will ALWAYS be there.
Politics, greed, and religion are still the main threats we face since man began to think.

Answer 5

Think I've just about deciphered your question. John Joe.

I do think about the possibility of extra terrestrials, and I think they're almost certainly out there somewhere.

The universe is definitely FINIITE, don't care what anyone else on here says. It's expanding continually, so therefore cannot ever have been infinite.

Principal threats to humanity are (I would imagine) that we'll annihilate ourselves through war, get wiped out by a catastrophic virus or get hit by an asteroid.

Answer 6

The problem is that we homo sapiens sapiens are extremely homo-centric, so we imagine little green 'men', but they still have the basic 'necessities', arms, legs, heads etc.

We need to broaden our perspective as to what constitutes 'Life' before trying to reasonably answer this question.

Everything here, and 'out there' is 'Life', that is it is electro-magnetic energy condensed and compressed into the material that we observe throughout out 'Universe'. Read on a search of 'Life', 'consciousness', 'awareness'. You will find that very highly respected physicists, as well as meta-physicists, have developed some quite sophisticated ideas of atomic, molecular and cellular 'consciousness' or awareness. Quantum mechanics is leading towards an understanding of apparent sub-atomic particle 'awareness'.

So 'Life' clearly requires, demands even, a broader definition.

So.....with this in mind, and to try to answer your question, there is no doubt whatsoever that 'Life' exists beyond our
( relatively ) tiny, pretty, little Blue Planet. You can see it, and for the initial part, we have brought back hard evidence of it's existence from such places as the Moon and Mars.

Everywhere there is observable 'stuff', there is 'Life', from this obscure corner of the rather ordinary Milky Way galaxy, to the incredibly beautiful Horsehead Nebula ( look up some NASA images on it, and tell me that 'Life' does not exist there ! ), and beyond, to the very furthest extent of our ability to observe or even intuit.

The principle ( and only, really ) 'threat' to humanity is humanity. We have created this realm in which to have experiences of the physical, and the 'outcomes' that we observe and experience are all of our own making.

'We', by the way, does not just mean those of us manifesting here in these monkey suits we call homo sapiens sapiens. We are manifesting in all sorts of guises all over the 'place' all of the 'time'. So be careful, when we do finally get around to having 'Alien' contact, we may just find ourselves looking at ourselves in the mirror !

The answerer who made references to 'other dimensions' has my total agreement as well, although he/she may or may not agree with my scribblings above. ;-)

Answer 7

I believe there is life on other planets. I think they're just hiding from us, afraid that we'll mess up their planet as much as we've managed to mess up our own.

As for, what is the principle threat for humanity? It has to be humanity itself. We're messing up the planet and are too blind to see it!!!

Answer 8

Is possible to be ET life.
We don't know ,yet, if The Universe is finite or infinite.
Principal threat for the humanity is humanity itself.
Yet.
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Answer 9

There are several parallel universe's, each with their own life forms