Where Are They Indeed?

George Rebane

There are about 2,500 galaxies (not stars) in the picture below – each of even the smallest dots is a galaxy.  Each such galaxy has about 300 billion stars, and each star has at least five planets.  Today we can see over 2,000,000,000,000 = 2 trillion such galaxies.  Fainter galaxies exist but don’t show in such photos.  This means that we can visualize only a part of our universe which itself contains 3x10^23 (a 3 with 23 zeros following it) planets.  Of these, at least 1% are in the ‘Goldilocks’ zone from their sun.  This suggests that there are about 3x10^21 planets that could potentially have an environment that supports life as we know it. (There are undoubtedly other forms of life about which we are ignorant.)  In our own galaxy there are about 11 billion of such planets.

To further illustrate the vastness of our visible universe, consider that the above photo is a magnification of what our telescopes see when looking at a part of the entire sky surrounding Earth that is less than 1/33 of (or more than 33 times smaller than) the size of the period at the end of this sentence when held out at your arm’s length.  This means if you printed a page with a period (from Times New Roman size 12) on it, and made a hole with a very sharp needle through and exactly the size of the period, then holding it out at your arm’s length you would be able to ‘see’ over 84,000 galaxies through that pinprick, no matter in which direction you looked in the night sky.  Of course, your eye would have to have the magnifying power of a big telescope (like the Hubble) to resolve all those galaxies as shown in the above photo.  Perhaps this understanding would allow us to better contemplate the size of our visible universe and consider all the extra-terrestrial civilizations that have already existed, are now in existence, and will come to be in the interminable future.

The background to this meditation was posted as ‘A copernican answers Fermi’, and later I’ll have more to say about the portents of all this. (more here)

Comments

[L]

Light speed is a real problem. Until we get past that detail, I'll go with "We're the first!"

[Barry Pruett]

Are we simply limited by our senses? And our basic observable universe in three dimensions? When you think about the distances, the numbers and times to travel or the vastness is insane. One of my favorite examples to understand the vastness is that a basketball in New York (to scale “the sun”) and a basketball in the beach in Hawaii represent to scale the distance between us and the nearest star. Damn.

[J. Barron]

Barry-
Toss in a time warp and the basketball from Hawaii could be in New Jersey.

[Michael R. Kesti]

Another relevant question is, "When are they?" The observable universe is thought to be about 13.7 billion years. That's plenty of time for life to develop and die out on those 3 X 10^21 planets long before we Earthlings might have noticed.

[Todd Juvinall]

I watched a program on the Hubble telescope and they ran an experiment to see what the vastness and number of galaxies might be. They focused the telescope into a straw width and pointed it at a place in space for three days. When they finished the estimate was something like a million galaxies in that little straw width. Amazing.

[Bill Tozer]

Light years? Not necessary. Just figure out what is beyond time and space.

[Scott O]

All of this ignores the issue of different dimensions.
We live in 3 of them. And add time. We are just beginning to understand what we can physically perceive. Quantum physics punctures a huge hole in our knowledge base. I won't get all hyper about the issue. We move forward based on what we know. Sometimes we have to step back and acknowledge a misunderstanding. Always hold fast to what you know and look forward to what you don't.
It isn't easy.