The Big Bang and the horizontality of science

in #science5 years ago

As we go outdoors at night, we can see the sky covered with stars. There are millions of them, if we try to count them we would lose count very quickly. Many of them are part of our galaxy, which is a grouping of billions of stars known as the Milky Way. The name comes from the fact that the Greeks saw it as a white patch crossing the sky, which gives an idea of what light pollution hides from us today.


(CC BY 4.0, by Beletsky)

There are billions of galaxies similar to the Milky Way in the universe

Now, according to legend, seeing an apple fall into the moonlight, Isaac Newton wondered

If the apple falls, why doesn't the Moon?


Isaac Newton (PD)

The answer, which led Newton to discover the laws of Mechanics, is relatively simple: as the Moon rotates around the Earth, the centrifugal force generated by such rotation prevents gravity from bringing it down on us.

But then this begs the first question why don't galaxies fall on top of each other? Certainly they attract each other with the force of gravity. Are they rotating around a common center? The answer is, paradoxically, no. Although galaxies rotate on themselves, thus preventing the stars that compose them from precipitating towards their centre, they are not in turn revolving around some hypothetical centre of the universe.

But then _why don't they fall? _

That mystery was solved by Edwin Hubble and Milton Humason, who discovered that galaxies are moving away from each other at great speed. In other words, galaxies don't fall into a common center, just as an object that we just threw up doesn't fall into the earth while it's still rising. While gravity is pulling on galaxies, their initial velocities cause that they do not go immediately down.


Edwin Hubble (PD)


Milton Humason (FU)

The story of Hubble and Humason's discovery is very interesting. Hubble was an astronomer. Humason was a donkey guide. Seriously. He met Hubble when a telescope was being built on top of Mount Wilson, while he guided the donkeys that carried the pieces to the site. Hubble was impressed with Humason's intelligence and incorporated him into his team. And they made one of the most impressive discoveries in human history.

How did Hubble and Humason know that galaxies are moving away from each other? They used a phenomenon known as the Doppler effect, which manifests when the source of a wave is moving.

  • In sound waves, the Doppler effect is what lets us know when an ambulance that was approaching to us starts to move away. As the ambulance comes towards us the sound is high (because the ambulance pushes the sound waves, and compresses them). When it begins to move away, it becomes more low (because the ambulance pulls them, and dilates them).

  • In electromagnetic waves, such as light and radio waves, there is also a Doppler effect. If a light bulb approaches us, it compresses the light waves it emits and makes them bluer. If, on the other hand, it moves away from us, it drags the waves behind it, making them redder. This allows us to know whether a distant light, such as that emitted by a galaxy, is approaching or moving away from our position.

Hubble and Humason noticed that the light from distant galaxies is slightly red, and that it is redder the further away the galaxy is. That means that galaxies are moving away from us, the faster the further away they are.

In addition to explaining why gravity does not cause galaxies to agglutinate by falling on top of each other, Hubble's and Humason's discovery raises new questions: if galaxies move away, the furthest away at very high speeds, that means they were closer in the past. Well, but then _how close were they? _

  • If in the past they came too close, then at some point galaxies were not yet galaxies, but a disordered mass of stars.

  • And if in a more remote past they were even closer, then at some point the stars were not yet stars, but were mixed in a homogeneous sea of extremely hot plasma....

Aha! but then there was a past where the universe was completely filled with a soup of extremely hot stellar material. And such a scenario has observable consequences.

Indeed, when something is hot, it shines. In other words, it emits heat in the form of electromagnetic waves. Today we should be able to detect the heat emitted eons ago by the soup of particles that filled the universe. Well, can we do it?

The story of the discovery of that cosmic background radiation or cosmic microwave background is also a fascinating story.

It turns out that Bell engineers Arno Penzias and Robert Wilson were experimenting with a supersensitive antenna for satellite communications. The antenna had a damn buzz that they couldn't eliminate no matter how many filters and refinements they added. And they concluded that the noise was a real phenomenon and not an epureous effect due to the antenna itself.


Robert Wilson and Arno Penzias (FU)

A friend of Penzias had seen a manuscript that the physicist David Wilkinson intended to publish on cosmic background radiation ¡Voilá! What they were hearing was the echo of the Big Bang, the caloric radiation emitted in the past by that boiling soup of stellar material.


David Wilkinson (PD)

In other words, Penzias and Wilson found proof that the Hubble and Humason discovery could be extrapolated back into the past. They demonstrated that galaxies were so close that stars had no identity, and everything was a hot sea of stellar material.

But... Can you extrapolate back even further?

  • We know that sometime in the past the atoms were so close that they lost their identity.

  • And even further back, there was an era in which atomic nuclei did not exist, and everything was a plasma of protons, neutrons and electrons. To have been able to predict from that image the current amount of hydrogen, helium and lithium is one of the greatest successes of theoretical physics (and material for another post).

  • At some point in the even more distant past, matter was so tight that even gravity lost its identity. But of that Planck era we know nothing more.

The interesting thing about the story of the Big Bang, of Hubble and Humason and Penzias and Wilson and Winkinson, is that it shows the horizontality of science. Humason was a muleteer, Penzias and Wilson were engineers, Hubble and Wilkinson were scientists. And their contribution was crucial to solving the problem.

Because science is not "what scientists do", nor should anything a scientist does be called science. And credentials don't matter. Credentialism is one of the signs of crap sciencie, no serious scientist exhibits titles to prove a point. When science does not accept "alternative" opinions, it is not because they come from people without a scientist's degree, but because of a lack of proof.

  • Nobody cares if a homeopath is a doctor or not, as long as he understands that the dilution of a part in 10^23^ leaves us with nothing to dilute.

  • Nobody cares if a naturist has a degree in nutrition or not, as long as he understands that a child needs to eat fat.

That is to say, when a "dissident" opinion is questioned, it is because it must be compatible with everything else that is already known, not because of the absence of a title in who wields it. That is why the denunciation of science as a school of initiates is not only Manichean and self-indulgent, but also deeply mistaken.

We owe one of the greatest discoveries of the 20th century to a muleteer and two engineers, whom no one excluded from an imaginary ivory tower. But of course, Humason nor Penzias and Wilson pretended to "unmask a conspiracy", but they had the humility to learn whatever was necessary to prove their discovery.


(PD)

I close with a link to an old fictionalized post on my blog (in spanish) about the Big Bang.

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