Wednesday, June 14, 2017

How Big is the Universe and How many Stars and Planets are there?



1. So far, the most distant body we know of in the universe is GN-z11, a galaxy about 13.4 billion light years away. In other words, what we see of GN-z11 today left that body 13.4 billion years ago, which is not long after the birth of the universe, which occurred 13.8 billion years ago (see: The Most Distant Objects; The Farthest Reaches; The Age of the Universe).

 2. Time: If the universe were 1 year old today, the sun and earth would have formed about three months ago; life on earth would have begun about two months ago; dinosaurs would have roamed around the world for about one hour yesterday, then disappeared; the first hominoids would have appeared an hour ago, Cro Magnon man one minute ago; Columbus would have crossed the Atlantic a second ago.

3. Distances: One light year is about 9.5 trillion kilometers. So GN-z11 is located at 13.4 billion x 9.5 trillion kilometers from us. This is 127,300,000,000,000,000,000,000 kilometers = One hundred and twenty-seven sextillion kilometers (1,273 x 10 to the twentieth power).

(A billion is 1 followed by 9 zeros; (10 to the 9th power;
a trillion is 1 followed by 12 zeros; (10 to the 12th power;
a quadrillion is 1 followed by 15 zeros; (10 to the 15th power;
a quintillion is 1 followed by 18 zeros; (10 to the 18th power;
a sextillion is 1 followed by 21 zeros; (10 to the 21st power;
a heptillion is 1 followed by 24 zeros) (10 to the 24th power).

Einstein proved that superluminal speed is not possible. As long as Einstein’s is the final word, humanity must accept  that it is doomed to remain the prisoner of the solar system forever: Our closest neighbor stars are between 4.2 and 8.5 light years away (Alpha Centauri, Sirius, etc.). Today, our fastest space ships reach speeds of 60,000 kilometers per hour. Let’s assume, optimistically, that we’ll be able to increase this tenfold in the future, to 600,000 kph. At that speed, it would take us 20,000 years to reach our closest neighbor! Eight hundred generations of astronauts would have to survive while traveling on those ships, arriving at their destination as far in the future from now as Neanderthal man lived in the past! And that is just to reach our closest neighbor, in our own tiny corner of our galaxy!

4. How large is the universe? Astronomers estimate that the OBSERVABLE universe may be 93 billion light years in diameter. There is some agreement on this. (See The Observable Universe). 

Some of the cosmological statements to which many experts subscribe are difficult to comprehend. I can only share them with you, and let you ponder them, as I do:

● Many astronomers believe that the universe is finite. There are those, though, who still maintain the common-sensical view that the universe is infinite. After all, if the universe has an edge, what lies beyond it?

● We are also told that the universe began at a specific moment. A “singularity” occurred, a disturbance in the electro-magnetic field, a “Big Bang.” As stated previously, this happened some 14 billion years ago. What then, was there before?

● It is also believed that the universe is flat. So when we hypothesize that the diameter of the observable universe is 93 billion light years, its  size is not a volume, but an area, which would be its radius (46.5 billion) squared and multiplied by 3.14 (Pi) = 6,789,000,000,000,000,000,000 “light years square,” or 6,789 quintillion (6,789 x 10 to the eighteenth power).

As to the size of the “entire” universe, no one knows. Some hypothesize that, if it is not infinite, its diameter is twice that of the known/observable universe, or 180 billion light years. Others go as far as 250 times larger.

It is more meaningful  to talk  about the observable universe. If we tentatively accept that it has a diameter of 93 billion light years, this is seven times further than that most distant galaxy, GN-z11. 5.

5. How many stars and planets are there in the observable universe? (See: How Many Stars Are There?)

First, we must answer the question: How many galaxies are there? (See: How Many Galaxies Are There?) Estimates range from 200 billion to 2 trillion, so let’s take a somewhat middle position, say, one trillion.

Next question: How many stars are there in an average galaxy? (See How Many Stars Per Galaxy?). Estimates for the Milky Way range from 100 billion to 400 billion. Again, let’s take the middle position - 250 billion.

The Milky Way is also believed to have a similar number of planets. I find this odd, since our own Sun has at least eight planets. However, I’ll defer to astronomers’ expertise. Maybe they figure that many stars are planetless...Or maybe their low estimate is due to the fact that we have yet to discover the vast majority of extra-solar planets.

 At any rate, if our galaxy is of average size (it is actually somewhat above average) then the total number of stars in the observable universe would be : 1 trillion x 250 billion = 250 sextillion (25 x 10  to the twenty-second power)), and the number of planets would be about the same.

To me, this incredible number of stars and planets makes it almost a certainty that there are other intelligent life forms in the universe. The only problem is that they, too, are forever stuck in their own star systems. That is why we should not expect any extra-terrestrial visitors.

6. The density of stars (and planets) in the universe: Were the diameter of the entire universe only twice that of the observable universe, its area would be 4 times as large, which would amount to almost 35 sextillion “light years square,” i.e. 35 x 10 to the twenty-first power. However, recall that some experts speculate that the entire universe is 250 times larger than the observable universe. (See Size of the Real Universe). This would give it a size of over 2 heptillion light years square, or 2 x 10 to the twenty-fourth power. Remember that the universe, just like galaxies, is flat (see Shape of the Universe).

Getting back to the OBSERVABLE universe, the question which puzzles me and which I cannot answer is this:

7. How does the observable universe accommodate 250 sextillion stars and 250 sextillion planets? If the observable universe has an area of 6,789 quintillion light years square (6,789 x 10 to the eighteenth power), then each light year square would, on average, have to contain 37 stars (along with its planets, moons, asteroids and whathaveyou).

But here in our neck of the woods, our closest neighbor stars are 4.2 and 8.5 light years away. Our sun is surrounded by an immense Oort Cloud, a field of particles that extends as far as one light year out from the sun. This vast area “belongs” to our solar system. Presumably, other stars also enjoy plenty of space. 37 stars per light year square seems impossibly crowded.

Another complicating factor is that the observable universe contains objects which no longer exist!

In conclusion, my numbers don’t seem to add up correctly. You are all invited to help me straighten this out.
© Tom Kando 2017;All Rights Reserved
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