The limits of quantum computing

Alan Turing

In an interview in a major Spanish newspaper (La Vanguardia) published on July 27, 2019, David Pérez García, a researcher in quantum physics, says this: We are just in the beginning of some technologies that we still don’t know how far they will go. He is right, because the future is hardly predictable, but when it comes to quantum computing we tend to think that these computers, if they are viable, will let us solve problems quite different from those that can be addressed by the traditional computers to which we are used. In this context, however, mathematics can help us distinguish between what can be done, and what is completely impossible.

Although quantum computing is a fairly modern concept, its theoretical foundation was established by Alan Turing during the 1930s. Let us review a little of what he showed, for in this way we can correct a few optimistic ideas spread by the media, often driven by experts who approach the issue from very different points of view, compared to Turing.

The optimism of Teilhard de Chardin

Pierre Teilhard de Chardin

Teilhard de Chardin’s vision of the future is essentially optimistic, perhaps too much. In his book The Phenomenon of Man he outlines his vision of the future evolution of human beings, which he presents as a process of increasing convergence towards a unifying center with the appropriate name of Omega Point.

By studying the unifying process that should take us to the next stage (or the final point) of our evolution, Teilhard distinguishes three different areas:

Anniversaries of space exploration

Armstrong, Collins & Aldrin - Photo NASA

Fifty years after the arrival of man on the Moon, a couple of European sexagenarians remember the first landing:

“Do you know what day is today?”

“Saturday, why?”

“I mean the date.”

“July 20th 2019, what about it?”

“Exactly fifty years ago, man reached the Moon.”

“Oh yeah! But wait, there is something wrong here, didn’t they arrive on the twenty-first?”

"No, it was the twentieth, but it took them over six hours to get down from the capsule. By then, in Europe it was the twenty-first, but in the United States it was still the twentieth.”

“True! I remember it well. I saw it on TV. I was ten years old.”

“Me too.”

George Ellis and the multiverse

George Ellis

George Ellis is a South African cosmologist who rose to fame almost half a century ago when he wrote a book together with Stephen Hawking (The Large Scale Structure of Space-Time, 1973), today considered a classic.

In an earlier post in this blog, published in November 2014, I mentioned that there are six independent theories about the multiverse, almost all of them incompatible with each other. In a recent article titled Theory Confirmation and Multiverses published in the book Why Trust a Theory?, edited by Radin Dardashti, Richard David and Karim Thébault (Cambridge University Press, 2019), George Ellis updates the different multiverse theories. He does not mention six, as I did five years ago, but nine, although he has left out one of the six I mentioned in my post (Smolin’s), perhaps because this theory has been abandoned in the meantime. The nine theories are: