Probability of the existence of extraterrestrial life

In a previous post I talked about the probability of the existence of extraterrestrial intelligence and mentioned the difficulty of its calculation, as we don’t know of any planet where they exist, apart from Earth, and to calculate the probability of an event one must know the number of favorable cases and the number of possible cases. For extraterrestrial life, we ​​don’t know either.

In another post I detailed the conditions that should be necessary if life similar to ours were to be possible on a planet similar to Earth. These conditions are many, which reduces the probability that we will find life on some extrasolar planet located in our vicinity. In fact, among the almost 10,000 planets detected so far (of which just over half have been confirmed), 65 are at a distance from their star that could be favorable for life (the Goldilocks zone), but only three of them orbit around stars similar to the Sun (of the stellar class G).

Another conversation with ChatGPT

As I said in the previous post, last January I did two sessions with ChatGPT from OpenAI. In the second, my questions were directed to the following scientific topics:

• The special theory of relativity, the limit of the speed of light in a vacuum, and the possibility of traveling in time.

Throughout the session I was asking the following questions:

1. Can a particle travel at a speed greater than light?

Answer: According to the theory of relativity, as first described by Albert Einstein, nothing with mass can travel at the speed of light...

The most surprising scientific failures

Lord Kelvin

The magazine Science News has published an article entitled Here are the 10 ten times scientific imagination failed, either because it fell short, or because it went too far, with respect to what it was logical to imagine. The study begins by quoting Albert Einstein:

Imagination is more important than knowledge... Imagination embraces the entire world, stimulating progress.

Tom Siegfried, author of the article, adds:

And yet while sometimes spectacularly successful, imagination has also frequently failed in ways that retard the revealing of nature’s secrets. Some minds, it seems, are simply incapable of imagining that there’s more to reality than what they already know.

Then he specifies one by one the 10 cases where, according to him, the imagination of scientists fell short or went too far. This is the list, from most to least important (according to Siegfried):

Can time travel paradoxes be avoided?

Cover of Fantastic SciFi with a
Porges story (The Shadowsmith)

In a science fiction story written in 1962 by Arthur Porges, entitled The rescuer, the inventors of a time machine discover that a man has entered the machine to travel back in time. To stop him, they destroy the machine with the man inside. When they are tried for murder and destruction of valuable property, they explain:

This man had taken with him a repeating rifle and five thousand rounds of ammunition. His intention was to arrive at Golgotha in time to rescue Jesus Christ from the Roman soldiers. In short, to prevent the crucifixion. And with a modern rifle, who can say he wouldn’t succeed? And then what?... What of the effect on the future, the entire stream of history, secular as well as religious?

The story is an excellent example of the paradox of predestination mentioned in a previous article, with several more that make us doubt the possibility of time travel. But is there no way to avoid the paradoxes? Is it possible to devise a theory that would remove them making time travel feasible, at least in principle? There have been several attempts to achieve this.

Will time travel be possible?

Hibernation in 2001, a Space Odyssey

The obvious answer to this question, such as it is formulated, is yes, of course it’s possible! We all travel in time at the rate of 24 hours a day.

Naturally, this is not what comes to mind when this question is asked. What is usually meant is this: will we be able someday to make sudden jumps in time, either forward (to the future) or backward (to the past)?

There are several schemes for traveling to the future. If they aren’t possible just now, one day they could become so. For example, perhaps human beings will be frozen and remain in suspended animation, to wake up and resume their ordinary lives a hundred years later. Or they could take passage on a spacecraft, make a trip at relativistic speed, and return to their starting point a century later, whilst for the travelers the elapsed time would have been just one year. In both cases, from the point of view of the persons in question, this would have been a trip forward in time, but in reality no sudden leap would have happened, for time would have kept going on for the hibernated body, though the mind would not be aware, and also for the relativistic traveler, although in this case time would have been accelerated.

But when we speak of time travel, we do not refer to these cases, which are possible in principle. We mean disappearing from the present and appearing in the past or in the future. Will we be able to do this someday?

Are we alone in the galaxy?

Enrico Fermi

In their famous book of hard scientific popularization, The Anthropic Cosmological Principle, published in 1986, the cosmologists John Barrow and Frank Tipler offer a proof that we are alone in the galaxy by means of a variant of the Fermi paradox (if there are any extraterrestrial intelligences in the Galaxy, why aren’t they here?) which can be summarized as follows:

1.      In 100 years we will have succeeded in creating life in the laboratory. Not just life, we will also be able to build a complete human being from its chemical components and information about the human genome, which can be stored in a digital memory.

2.      In 100 years we will have managed to build artificial intelligences as intelligent as human beings, able to replace us in any place and circumstance.

3.      Our current space technology allows us to reach a speed of 0.0003 c (where c is the speed of light). At that speed, a spaceship would take about 50,000 years to reach the nearest stars.