The inconstant constant

Georges Lemaître

In a previous post, The Hubble-Lemaître Law, I explained how Georges Lemaître discovered in 1927 the expansion of the universe, but as he published in a French-language journal, it didn't make a great impact, and for almost a century the discovery was attributed to Edwin Hubble, who published in 1929 in a much more widely circulated English-language journal. This injustice was corrected on October 29, 2018, by the International Astronomical Union, and I echoed the renaming of the law in my post, published three days later in this blog.

The Hubble-Lemaître Law says this: The farther away a galaxy is, the faster it is receding from us. Its recessional velocity is proportional to its distance. The constant of proportionality is called the Hubble constant, which has the dimension of 1/time. In the International System of Units, this dimension would be expressed as seconds⁻¹ or 1/second, but in practice, its definition (speed/distance) is used, with the following units: km/s/Mpc, which means: the increase in the recessional velocity of a galaxy (in km/s) as its distance from us increases (measured in Megaparsecs). One Megaparsec (Mpc) is one million parsecs, and one parsec is equal to 3.2616 light-years.

Paul Davies, popularizer of science

Paul Davies

Paul Davies came to the fore among scientists who devote time to popular science with his 1992 book The Mind of God, written in response to Stephen Hawking’s final words in his popular best-seller A Brief History of Time. In another post I talked about another of his popular books, The Eerie Silence. Here I am going to discuss two other books he has written.

The Last Three Minutes (1994): This book on popular science is a little behind the times, as it predates the standard cosmological model, but explains well the state of cosmology when the book was published, and many of the things it says are still valid. It says something very interesting: that the Big Bang theory by Lemaître (whom Davies does not name) should have been accepted long before its two surprisingly accurate predictions gave it a boost in the sixties, because there is another argument supporting it, that scientists of the 19th century should have noticed, but didn’t: If the universe were infinitely old, it would have died by now. It is evident that something that moves to a stop at a finite rate cannot have existed from all eternity. By the way, there is an error in this paragraph: Davies ignores the difference between what is eternal and everlasting, which was solved fifteen centuries ago by Boethius. And there is a major flaw when he says that the radius of the visible universe is 15 billion light-years, because he does not take into account the expansion of the universe. The correct radius is about 43 billion light-years.

Science was never a danger for my Catholicism - Part I

Interview with Manuel Alfonseca. Originally published in Spanish in La NuevaRazón

Questioner: Carlos Sordo de la Rubiera

I Part

Q: Most scientists are atheists. Myth or Reality?

A: I think this is not true. Since God is obviously not an object of study by science, many scientists, relying solely on science, hold that the correct position is agnosticism. But there are other ways, apart from science, that can make us know something. In general, there are three forms of knowledge: authority, experience, and reasoning. Scientific research is just one type of reasoning; apart from it, we also have, for instance, philosophical or artistic reasoning.

The hijacking of the Big Bang

The Big Bang theory was invented in 1931 by the Belgian priest Georges Lemaître, through the backward application in time of the Hubble-Lemaître law, discovered by Lemaître in 1927 and independently by Hubble in 1929. Indeed, if most galaxies are moving away from one another, because of the expansion of the space separating them, billions of years ago they must have been much closer, and at the limit all the visible universe would have shrunk to a point. We believe today that this happened about 13.8 billion years ago.

In 1948, George Gamow, Ralph Alpher and Robert Herman made two predictions that should be fulfilled if the Big Bang theory were true: the mass of the universe should consist of about 75% hydrogen and 25% helium; and there should exist a cosmic background radiation with a temperature of about 5º Kelvin. Other cosmologists, however, took this theory as a joke, and to make fun of it they gave it the name Big Bang, which although not quite appropriate, has remained fixed, perhaps forever.

My 10 Favorite Scientific Discoveries of the 20th Century

In a post published two weeks ago, I commented on an article in Science News that tried to answer this question: which were the ten most important scientific discoveries of the last century? Some of my readers asked what is my personal opinion. This is my answer.

To begin with, I will point out that scientific research can advance in four different ways:

1. Theoretical science, which tries to discover fundamental laws in the universe.
2. Experimental science, which confirms or falsifies theories by carrying out experiments.
3. Observational science, which instead of experimenting, observes. Astronomy, for instance, uses these methods, as experimentation is almost never possible.
4. Technology, the practical application of science, whose goal is to build devices that work.

The problem of the cosmological constant

Albert Einstein

The value of the cosmological constant Λ in Einstein's equation has gone through many vicissitudes and alternatives:

Scientific models: adjustment or validation?

Leonard Nimoy
as Mr. Spock

One of the ways in which science advances is by building models, which are often made up of more or less complex sets of mathematical equations, and trying to verify whether or not these models adapt to the functioning of the real world, as described by our senses and our instruments.

When building and using a model we must consider two distinct phases:

• Model adjustment: it consists of assigning values ​​to the parameters of the model to ensure that it fits the data we already have about the real world. A model not adjusted to such prior knowledge would be totally useless.
• Model validation: it consists of using the model to make surprising predictions that nobody could have foreseen without the help of the model. If these predictions are confirmed, they become surprising accurate predictions, validating the model. However, the validation is never final, for a new surprising inaccurate prediction could invalidate it in the future.

Let's look at a few examples:

Is there energy in the cosmos?

Georges Lemaître

During the 1950s two cosmological theories entered in competition: the Big Bang, proposed by Georges Lemaître, and the steady state, proposed by Hermann Bondi and Thomas Gold. Although the second had to renounce the principle of the conservation of energy, the most sacred of physics, atheist cosmologists preferred it to the Big Bang, as it seemed to them that this theory required to accept God's creation. In the words of the English astronomer Raymond Littleton, in his popularization book The Modern Universe (1956):

A theory such as this [the Big Bang] that puts back creation to a singular instant in the remote past... to some minds it is an objection that it would imply the removal of the question of the origin of the material of the universe from the realm of science... This consideration does not of course mean that the explosion theory is necessarily wrong, but it puts the act of creation, as we might name it, beyond the reach of science.

In other words: Raymond Littleton objects to the Big Bang theory because it could force us to recognize the existence of a creative God. It cannot be said more clearly.

4 clarifications about the history of the universe

James Peebles

Certain statements by James Peebles, recent Nobel Prize in physics, have aroused controversy, although what he said is not something new, as theoretical physicists have long been saying precisely the same thing.

The Big Bang theory was proposed in 1931 by Georges Lemaître, by extending to the past the Hubble-Lemaître law. In 1948, Ralph Alpher and Robert Herman predicted that, if the Big Bang theory is correct, there must be a cosmic background radiation with a temperature close to 5 Kelvin. In 1965 Arno Penzias and Robert Wilson discovered the existence of such cosmic radiation, whose temperature proved to be 2.72548 Kelvin. The temperature is exactly the same in all directions, except for two effects that cause small differences, but never affecting more than the third decimal place.

Media manipulation: the Nobel Prizes and religion

James Peebles

The 2019 Nobel Prize in Physics has been assigned to cosmology and divided among three scientists: James Peebles, a Canadian, who receives half the prize for his theoretical work; and Michel Mayor and Didier Queloz, who have shared the other half for having discovered the first planet outside the solar system that revolves around a star in the main sequence.

The theory of the Big Bang was proposed in 1931 by George Lemaître, as a consequence of the extension to the past of the Hubble-Lemaître law. In 1948, Ralph Alpher and Robert Herman predicted that, if the Big Bang theory is correct, there must be a cosmic background radiation with a temperature close to 5 Kelvin. In 1965 Arno Penzias and Robert Wilson discovered the existence of such cosmic radiation, whose temperature turned out to be close to 3 Kelvin. That same year, Robert Dicke, James Peebles and other collaborators reasoned that the radiation discovered by Penzias and Wilson is precisely the signature of the Big Bang predicted by Alpher and Herman. During the 70s, Peebles was one of the leading theoretical cosmologists who studied the field of the formation of the great cosmic structures (galaxies and groups of galaxies). For these works he has now been awarded the Nobel Prize.

The Hubble-Lemaître Law

Georges Lemaître

Let us look at a little history.

In various places in the sky, but especially in the constellation of Cepheus, where the first case was discovered, there are some stars whose light intensity varies regularly, and therefore are called variable Cepheids. In 1908, the American astronomer Henrietta Swan Leavitt discovered that the period of these stars is linked with their real luminosity: the greater the luminosity, the longer the period. Therefore, by measuring their period, their real luminosity can be deduced.

In 1913, the American astronomer Vesto Melvin Slipher obtained the spectrum of what was then called the Andromeda nebula (the giant galaxy closest to ours) and discovered a blue shift that indicated (according to the Doppler effect) that the nebula moves towards us with a speed of about 300 kilometers per second, much higher than expected. Slipher then studied the light of other spiral nebulae and made the unexpected discovery that most of them, unlike Andromeda, show redshifts, that is, they move away from the solar system with great speed. In fact, he measured speeds above 1000 kilometers per second.

In 1919, the American astronomer Edwin Powell Hubble used the Mount Wilson telescope to photograph several spiral nebulae, including Andromeda, and showed that, actually, they were not nebulae, as had been believed, but huge clusters of stars. From then on they were no longer called nebulae, but galaxies, in honor of our Milky Way, which also belongs to the class of spiral galaxies. Galactos in Greek means milk.