Sobaka.ru: Einstein’s theory of relativity refuted? New physics laws ahead? Here’s the explanation in simple terms!

What has happened?

Here is what happened: on 11 November, an article was published in the prestigious research journal Nature Communications. Its authors — respected scientists from the universities of Geneva and Toulouse — are trying to figure out how our Universe is organised (or rather, how it is expanding).

For almost 30 years, physicists have known that the Universe is expanding at an accelerated pace. In simple terms, the farther we are from the Big Bang in time, the faster galaxies are racing away from us. This is not because Earth is particularly unappealing — this pattern holds true anywhere in the Universe.

Over these 30 years, physicists have made many attempts to measure this accelerating expansion, which can be done in different ways and on different scales — by observing stars, galaxies, clusters of galaxies, and so on. In the last five years, cosmologists (scientists who study the evolution of the Universe — Editor’s Note) have encountered a pretty exciting challenge. Observational data from different scales do not align, and current theories fall short in accurately describing these objects. This mismatch is what I call an exciting challenge. It signals that scientists still have what to discover, pushing the boundaries of our scientific knowledge.

So, the authors of the article in question set out to determine at which scales this data mismatch is most pronounced.

What’s Einstein got to do with all this?

Einstein has to do with this conundrum because modern cosmological models, i.e. mathematical frameworks that describe how the Universe functions, are built upon his General Theory Relativity.

In the 17^th century, Sir Isaac Newton — inspired, as legend has it, by a falling apple — developed the theory of gravity we all learned in school. This theory perfectly explains the dynamics of our Solar System; yet, even Newton recognised its limitations when applied to the entire universe. The thing is, if gravity merely pulled bodies toward each other, objects in a finite universe would cluster around a single centre, preventing an even distribution of stars. However, we observe stars uniformly scattered across the sky. This implies that the Universe is infinite, a scenario Newtonian gravity struggles to describe consistently — a puzzle known as the gravitational paradox.

About a century ago, Einstein sought to address this puzzle by introducing a new theory of gravity. He proposed that space is not flat but curved, like a crumpled leaf. This groundbreaking idea enabled one of my scientific forebears, the Russian physicist Alexander Friedmann from St Petersburg, to develop a mathematical model of the Universe that, at the time, worked remarkably well. This model laid the foundation for all of modern cosmology.

Why are journalists claiming that the new study has "refuted" Einstein?

In reality, this is not the first time such claims have been made. Over the past five years, there has been much evidence suggesting that our current cosmological model, grounded in Einstein’s theory of relativity, may be too rigid. It fails to account for the subtle effects that astrophysicists observe in real data.

Take, for instance, the Hubble constant — a parameter that roughly represents the observed rate of the Universe’s expansion at any given moment. This constant can be measured using various phenomena across different scales, such as pulsating Cepheid stars and supernovae explosions. The fact of the matter is, these measurements often yield strikingly different values for the Hubble constant. Reconciling these discrepancies is one of the major challenges currently facing cosmologists worldwide.

How can we measure the expansion rate of the Universe?

One method involves using the phenomenon known as cosmological redshift. Physicists know that the signal emitted by an object changes depending on whether it is moving toward us or away from us.

"This effect is something we have all experienced," explained Anton Sheikin, Candidate of Physics and Mathematics and Associate Professor in the Department of High Energy and Elementary Particle Physics at St Petersburg University. "Think about standing on the side of the road as an ambulance speeds by. You will notice the sound of its siren changes slightly — it sounds higher-pitched as the ambulance approaches and lower-pitched as it moves away. The same principle applies to light. If an object is moving quickly toward you, its light will appear slightly bluer. Conversely, if it is moving away, the light will appear redder."

Hence, the degree to which stars or galaxies appear redder than calculated indicates how fast they are moving away from Earth due to the Universe’s expansion.

The authors of the article in Nature Communications examined the latest data and found that observational results do not align with the predictions of General Relativity. The fact of the matter is that the farther we look from Earth, the older the events we observe. This occurs because light from distant stars or galaxies takes longer to reach us than light from nearby sources (Editor’s Note).

The authors of the article demonstrated that while events from the earlier history of the galaxy — those occurring a very long time ago — align well with Einstein’s theory of relativity, more recent events do not fit as neatly into his framework.

"Our findings reveal that in the distant past, around 6 to 7 billion years ago, the depth of gravity wells (deformations of the Universe caused by the gravitational influence of celestial bodies like stars and black holes — Editor’s Note) aligns perfectly with Einstein’s predictions," said Isaac Tutusaus, Research Associate at the Institute of Research in Astrophysics and Planetology (IRAP) at the University of Toulouse and co-author of the article. "However, in more recent periods, around 3.5 to 5 billion years ago, these gravity wells appear slightly shallower than Einstein’s theory predicts."

Has Einstein been proven wrong?

In short, no. Over the centuries, we have become quite adept at applying the scientific method. As a result, it is rare to find well-established theories in modern physics that are completely overturned — that is, proven to be fundamentally flawed in all their underlying assumptions.

What truly happens to theories in physics? They evolve and are refined. Take Newton’s concept, for example. It still works exceptionally well within our Solar System, but it falls short when applied to much larger scales because it does not account for certain critical factors affecting celestial bodies. Yet, no one claims that Newton’s theory has been disproven. It is still taught in school, and it is the basis for many scientific calculations.

The same holds true for Einstein’s theory. It performs exceptionally well for relatively compact astrophysical objects like black holes and neutron stars. However, it struggles when applied to the ultra-large scales of the universe.

Consider the Nobel Prizes awarded over the last decade: two of them honoured research that confirmed General Relativity. In 2017, the prize was awarded to scientists who detected gravitational waves, and in 2020, it went to researchers studying black holes. In both instances, Einstein’s predictions were brilliantly validated.

In summary, the article in Nature Communications is highly significant. It tackles a pressing and fascinating question, marking an important step toward a new theory of gravitation. This theory, however, will not invalidate but rather complement and build upon Einstein’s General Theory of Relativity. So, there is no need to panic — our current physics textbooks will remain relevant.