Editor’s Note: Don Lincoln is a senior scientist at the Fermi National Accelerator Laboratory. He is the author of several science books for general audiences, including the best-selling audio book “The Theory of Everything: The Quest to Explain All Reality.” He also produces a series of science education videos. Follow him on Facebook. The opinions expressed in this commentary are solely his. View more opinions on CNN.
Perhaps the oldest and grandest question asked by humanity is “How did the universe come into existence?” Indeed, proposed answers to that puzzle are found in ancient religious texts, some thousands of years old. In the modern era, that question is more properly considered to be the province of science.
However, a recent astronomical measurement recorded in a laboratory at the South Pole is causing scientists to revisit their theories. While those people who crave certainty in their life might be unhappy because of the new measurement, it’s important to remember that there are no sacred cows in science, and scientists are always checking and rechecking even their favorite universal models.
The current scientific explanation for the origin of the universe can be dated to about 13.8 billion years ago, when the entire visible universe was compressed into a volume much smaller than an atom. Something – and we don’t yet understand exactly what – caused it to expand in an unfathomably hot and explosive maelstrom called the Big Bang. The universe has been expanding ever since, a fact that astronomer Edwin Hubble discovered back in 1929.
In the intervening decades, observations have only strengthened the case for the Big Bang theory, but they have also made it clear that the theory is incomplete. For instance, in its earliest incarnation, the Big Bang couldn’t explain why the universe was so uniform. Astronomers in the Northern Hemisphere who looked deep into space see the same thing on average as ones that live in the Southern Hemisphere. Traditional Big Bang theory predicts that there should be small differences in temperature, clumpiness of large clusters of galaxies and other properties. But both sides look the same.
However, in 1980, physicist Alan Guth proposed an extension to the theory that could reconcile some of the inconsistencies between theory and observation, including the unexpected uniformity. His extension is called cosmic inflation theory and it claims that in the first moments of the birth of the universe it expanded faster than the speed of light. In a tiny fraction of a second, the visible universe grew from the size of an atom to a sphere roughly a light year across.
Subsequent astronomers invented variations of inflation, of varying degrees of complexity, but they all predict that the early universe expanded at unfathomable speeds.
The principle of inflation has long been considered an important component of the modern scientific theory of how the universe began, but it has never been experimentally confirmed – so it remains a speculative idea.
However, if inflation is true, we should be able to prove it. Although the universe was once glowing hot, the expansion of the universe has cooled it off and that glow has morphed into microwaves that astronomers have been able to detect since 1964. This relic of the Big Bang is called the cosmic microwave background, or CMB.
Inflation theory predicts that the microwaves of the CMB should be polarized. Just like ordinary light, microwaves are just wiggling electric and magnetic fields and if the wiggles are oriented in specific directions, the result is polarization. The CMB can be polarized in two ways: B-modes, which are swirly patterns, and E-modes, which are more of a straight-line pattern. And, if inflation theory is correct, we’d expect to see some mix of B-modes and E-modes, while if it isn’t correct – in other words, if the expansion of the universe did not happen as quickly as the theory suggests – researchers should only see E-modes. This is because B-modes are caused by gravitational waves that would have shaken the early universe and would have been locked into our universe by inflation. Without inflation, we’d not see those primordial gravitational waves – the evidence for them would have dissipated away.
Astronomers used a telescope facility called BICEP-3 (short for Background Imaging of Cosmic Extragalactic Polarization) to study the CMB and its polarization. The telescope’s South Pole location, with its altitude of nearly two miles above sea level and incredibly dry air, is an ideal place to conduct this kind of research. BICEP-3 scientists combined their data with measurements at other facilities and found no indication of B-modes originating from the CMB. If B-modes are present in the CMB, they are very small.
So, does that mean that the theory of inflation must be thrown out? No, although the data has disproved some of the simpler theories of inflation, it isn’t sensitive enough to rule out the more complex versions. Still, the failure to observe CMB B-modes is unsettling, causing some scientists to go back to the drawing board.
There are those who are discomfited when a scientific measurement draws into question a theory that is popular among researchers, but they shouldn’t be. The self-correcting nature of science is actually its strongest asset.
Scientists are constantly double-checking their own ideas and, even if they don’t, other scientists do it for them. The goal is to get at the truth. Indeed, a good scientist should never hold firmly to their ideas and should be open to changing their viewpoint as more data comes in. Slowly, but surely, scientific ideas are refined by this process, getting closer and closer to the truth.
In many ways, this recent BICEP-3 result is like the situation with Covid in early 2020. Initially, scientists told us that we needed to disinfect all of our groceries and that masks weren’t that important. However, as more research was performed, scientists found that their initial advice was incorrect. Over the last year and a half or so, doctors learned and modified their approach to the disease.
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Similarly, improved measurements like those made by BICEP-3 might one day confirm inflation theory, but equally well those future measurements could one day kill it.
But that’s OK. Scientists will put on their thinking caps and come up with a newer and better theory, and we’ll be closer to the truth. Change is inevitable.