Wednesday, June 14, 2017

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

With assistance from Dr. Gene Barnes

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 7,750  years to reach our closest neighbor! Three hundred and twenty  generations of  astronauts would have to survive while traveling on those ships, arriving at their destination as far in the future from now as the dawn of civilization occurred 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). 

Here are some  cosmological/scientific questions  for you to think about, with fascinating comments and explanations  from Dr.  Gene Barnes,  a friend and a retired professor of physics  who understands this subject far better than I do:

Is the universe is finite or infinite? Common sense suggests that it is infinite. After all, if the universe is fenced in, what lies behind the fence?

Did time and the universe have a beginning?  Here, too, our comon sense suggests that they did NOT. After all,  if there were a beginning to “things,” what then, was happening BEFORE?

However, we are told by scientists that the universe is both finite, and that it began at a specific moment - about 14 billion years ago.  A “singularity” occurred,  a disturbance in the electro-magnetic field, a “Big Bang.”

Here is what Gene writes:

The question of whether the universe is finite or infinite is really a philosophical question rather than an astronomical one. However, it is generally thought by astronomers that time and space were both created by the Big Bang event, and may therefore only exist within our universe. If so, we could only receive information from within our universe.  What might or might not lie outside it would only be a theoretical speculation.  As for the concept of infinity, it is just a mathematical limit abstraction used to simplify calculations—whether any real physical entity corresponding to it exists could never be confirmed (as it would require infinite time to do so.). Science is based on finite observation rather than belief—hence it is always conditional, subject to possible correction by future observations.

A third puzzling notion: It is sometimes  stated  that the universe  is  flat.  But this is misleading to the layperson.  See for example What Do You Mean, The Universe is Flat? Gene explains things this way:

“The word flat is sometimes used to describe space, but it does not mean that space is two-dimensional. It only means that it is not warped by gravitation as it would be near a massive star. It simply means that a flat space is Euclidean—like our space on or near the earth. (If the universe were really flat we would not see different stars in all directions all around the earth.)”

It relieves me to hear  this, because if we really lived in a flat universe, our world would be like the one described in  Edwin Abbott’s famous book “Flatland”  (published in 1884).

So, to answer the question “How large in the universe,” let us reduce this to the more  meaningful question “how large is the OBSERVABLE universe, and let Dr. Barnes give the answer:

The best definition of the size of the Observable Universe is that volume from which we can receive signals (for example, starlight, and microwave radiation from just after the big bang event.) Currently this appears to be a spherical volume (Not a Flat Surface) with a radius of 46.5 Billion LY.  I say “currently” because the universe is expanding, and if the expansion rate is less than the speed of light, more distant signals may become visible in the future. The rate of expansion is thought to have been variable in the past, and may even have exceeded the speed of light for a time. Thus, signals from some light sources may never reach us.

So the current diameter of the universe is about seven times greater than the distance between us and the farthest galaxy we have  ever observed - GN-z11.

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. Our own Sun has at least eight planets, so one might expect that there are far more planets than stars in the universe. However, there are probably many planetless stars. Also, astronomers have so far only discovered a few thousand exo-planets (planets outside the solar system).

 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.

But mt colleague Gene Barnes is more skeptical. Here is what he writes:

Estimates for the number of planets in the universe are pretty speculative, because they depend on such a large number of factors. Only certain types of stars would be expected to have any planets at all. So the estimates depend on the number of these stars in a galaxy, and the number of galaxies in the universe, as well as the average number of planets around a certain type of star. This is mostly theoretical prediction, rather than observation. To date, only 4034 exo-planets  have been observed, of which only 50 seem to have suitable conditions for habitation. Personally, I don’t think that extrapolating from 4034 to 250 sextillion planets is justified. The sample is just too small! 

And regarding extra-terrestrial intelligent life, here is what he writes:

As to whether there is other “intelligent” life in the universe, we have no actual data at all.  Years ago, Professor Drake made a calculation about the odds on this, using some of the then-known factors, but in my opinion it is not possible to accurately calculate the probability of an event that has never occurred! (Even the assumption that life on earth is “intelligent” might be difficult to prove.)

Ouch! That last sentence hurts those of us who thought that at least some of us humans (Socrates, Da Vinci, Descartes,  Mozart, Einstein, a few others) were pretty smart!
© Tom Kando 2017;All Rights Reserved
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