How the Big Bang Model Grew in the History of Physics

From the Lecture Series: The Big Bang and Beyond: Exploring the Early Universe

By Gary FelderSmith College

It’s incredible when one thinks of the fact that we have discovered so much in the history of physics that we have described events that lasted for a fraction of a second almost 14 billion years ago, used those descriptions to make detailed predictions, and then successfully tested those predictions with further observations.

Concept of history of physics
Starting from Issac Newron’s era, physicists had a pretty much different idea regarding the history of the universe than later on in the 20th century. (Image: Lia Koltyrinai/Shutterstock)

From Newton to Einstein

Our description of the universe from 13.8 billion years ago until today has made many predictions that have been borne out by observation. How did the big bang theory come about? Most of us grew up hearing about the big bang, but the whole idea is fairly recent in the history of science.

From the time of Isaac Newton in the 17th century, most physicists believed the universe was eternal and unchanging. The stars appear to rise and set and go through other apparent cyclic motions, but those could all be explained as effects of the rotation and other motions of the Earth. Once you took the Earth’s motion into account, the heavens beyond our solar system seemed to be static.

Fast-forward hundreds of years to 1915. That’s when Albert Einstein published his general theory of relativity, which described the nature of space, time, and gravity. Einstein’s theory was confirmed by a number of experimental tests.

But when Einstein applied his theory to the universe on large scales, it made a prediction that didn’t seem to match what astronomers knew about the universe. The equations of general relativity said that a static universe was impossible. According to Einstein’s theory, the universe could be contracting or expanding but not staying still.

What Einstein Got Wrong

Since all the astronomers of the time believed the universe was static, Einstein modified his theory by adding a new term called the cosmological constant to his equations. This change was intended to allow for a static universe. But later calculations showed that even with the cosmological constant, the universe, according to general relativity, still had to contract or expand.

Georges Lemaitre and Albert Einstein standing next to each other
Albert Einstein’s (right) judgment on Georges Lemaître’s (left) physics was later proved wrong. (Image: Unknown/Public domain)

In 1927, a Belgian priest named Georges Lemaître published calculations that described what an expanding universe would look like based on general relativity. Observers in any galaxy would see other galaxies moving away from them, with distant galaxies moving away faster than nearby ones. Mathematically, the speed at which we would see another galaxy moving away from us would be proportional to its distance from us.

Einstein still believed the universe was static and told Lemaître that his physics was “abominable”. But two years later, in 1929, Edwin Hubble measured the speeds and distances of 24 galaxies. Hubble found that almost all of them were moving away from us at speeds proportional to their distances. In other words, the farther away from us a galaxy is, the faster it moves away, exactly as Lemaître had described.

That kind of match between mathematical predictions and measured data is what you need to gain acceptance for a physical theory. Hubble’s data convinced most physicists that the universe is expanding, and Einstein went out of his way to publicly praise Lemaître’s work after that.

This article comes directly from content in the video series The Big Bang and Beyond: Exploring the Early UniverseWatch it now, on Wondrium.

The Big Bang Theory’s Popularity in the History of Physics

Illustration of the universe’s expansion from the singularity
Lemaître not only described what an expanding universe would look like but also proposed that the universe expanded from an initial hot state. (Image: Fredrik/Public domain)

The pattern of distant galaxies moving away from us faster than nearby ones came to be called Hubble’s law. But in 2018, the International Astronomical Union voted to rename it the Hubble-Lemaître law. Two years after Hubble’s measurements, in 1931, Lemaître published a paper tracing the expansion of the universe backwards to an initial hot, dense state. Lemaître’s term for this cosmic starting point was the primeval atom.

For several decades after Hubble’s discovery, however, a number of skeptical physicists continued to believe that the universe must be static. In fact, the name we now use for Lemaître’s primeval atom was originally coined by one of these skeptics, Fred Hoyle, who in a 1949 radio interview referred derisively to the idea of the universe being created in a “big bang.”

As more evidence accumulated, though, the number of skeptics shrank. The decisive turning point was in 1964 when astronomers detected background microwave radiation of exactly the sort predicted by the big bang model. This was a match between theory and experiment that was too strong to ignore. 

Since the 1960s, there has been no serious scientific debate about the fact that the big bang model is an accurate description of the history of our universe over the past roughly 14 billion years.

Common Questions about How the Big Bang Model Grew in the History of Physics

Q: What happened when Albert Einstein applied his theory of relativity on a large scale?

When Albert Einstein’s equations were applied on large scales, their results implied that the universe isn’t static. To fix this, Einstein added a cosmological constant to his equation, but the equations still didn’t support the notion of a static universe.

Q: How did Georges Lemaître affect the notion of an expanding universe?

Georges Lemaître used Albert Einstein’s general relativity to describe how the universe would work if it were expanding. Though Einstein himself didn’t agree with Lemaître at first, he was eventually proven right after Edwin Hubble’s observations were published, making a mark in the history of physics.

Q: Why was the Hubble law renamed in 2018?

The pattern of distant galaxies moving away from us faster than nearby ones came was called the Hubble law. Since Edwin Hubble was not the only person responsible for this amazing discovery in the history of physics, the International Astronomical Union voted to rename it the Hubble-Lemaître law.

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