In Mexico, Cosmologist Hunts for Cracks in Einstein’s Gravity Theory

During a solar eclipse in 1919, Arthur Eddington observed light bending around the sun just as Albert Einstein predicted. General relativity says that stars warp the fabric of space-time around them. A year rarely goes by without a new experiment or observation. There is a hitch.

Dark matter and dark energy make up a large part of the universe. The assumption is that dark matter and dark energy are nonluminous particles. It is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556

The woman is looking for a more complete theory. Over time, there have been many alternatives to general relativity, from teleparallel gravity to complex quintessence. The ideas have gathered dust due to the inability of cosmologists to create experiments that can distinguish these theories from general relativity.

She is a pioneer in her home country of Mexico in the field of precision cosmology. Thanks to the data, you can see which theories work and which don't.

We can find cracks in general relativity by looking at the early universe and black holes. This isn't conventional wisdom, but the path to becoming a cosmologist hasn't been conventional either.

Ciudad del Carmen is a city on a small island in southern Mexico. She remembers walking along the beach at night as a child, wondering why the moon was round. She wondered why it only comes out at night.

She switched her focus to cosmology after watching one of her university professors calculate the age of the universe. She said that these are careers for people in the United States.

At 29, she was invited back to Mexico to run the theoretical physics department of the Mesoamerican Center for Theoretical Physics, after completing her doctorate in Europe and the United Kingdom. She was the first woman to hold a research position in the department of gravitation and field theory at the UNAM.

We talked for four hours. From her office at UNAM in Mexico City, she was confident and enthusiastic about the potential of precision cosmology to overturn Einstein. The interview has been edited for clarity.

General relativity and the standard model of cosmology that grew out of it work so well. Why do you think we need to modify or extend gravity?

General relativity is not general enough. If you want to explain dark energy, you need an extra component in the equation called the cosmological constant. You need to add it by hand because it doesn't exist naturally.

There is a theory that can give you dark energy. I'm working on these theories of gravity because of that.

Other than dark energy, what other puzzles could these theories solve?

General relativity explains a lot about nature, but it doesn't explain what happened inside black holes. The point where all the known laws of physics break is called the black hole's singularity. If we modify or extend general relativity, we might be able to explain the strange point that breaks everything.

General relativity doesn't explain the future of the universe. The Big Crunch universe is one of the interesting theories that say the universe is going to collapse again. We don't know because general relativity is incomplete. We could get answers to these questions if we found a complete theory.

There’s broad agreement that a fundamental, quantum theory of gravity is needed to describe black hole interiors and the Big Bang. The usual assumption, though, is that quantum gravity looks like general relativity throughout the rest of the universe. But you think a different theory will work better everywhere. Can you give an example of how modified theories differ from general relativity?

There are theories. These are not the same as general relativity. Why? General relativity describes space-time using a mathematical object. There are also objects in the theories. The space-time can be something physical, like mass or energy.

So it behaves a bit like the cosmological constant in general relativity?

Exactly. You don't add anything in this theory because of the mathematics.

This isn't the only alternative. There was an explosion of these theories in the 1980's. With so many theories at hand, we were limited by experiments to tell them apart.

Is this what led you into precision cosmology?

The explosion of precision cosmology in Europe was the year I received my PhD. Ten years ago, the standard process was to take a telescope and make observations, with this data you tested your theory. We have many telescopes that collect data from different parts of the universe. We can process all this data with machine learning. The test of a theory is richer because of that.

I am the first person to publish a paper that uses machine learning to study dark energy. Machine learning architectures can look at large data sets to derive a theory of gravity. This is a new era.

Simulations on a supercomputer are a new way to test alternative theories. You can make predictions about which theory will work in your universe.

What brought you back to Mexico after studying in Europe?

I was finishing my post in England when I got a call from the Abdus Salam International Center for Theoretical Physics that said they were opening an institute in Mexico and needed Mexicans who were studying in Europe to come back.

There was no one in Mexico who could do precision cosmology using statistics. It was fresh air for many of my colleagues when I arrived. I had learned a lot in these other countries.

Four years ago, I received a call from UNAM. I knew I could form a new research group in my country.

What challenges have you faced in building this research group?

Some people in the university community thought that physicists only need paper and a pencil. It is more than that. You need to travel to meetings to build relationships and collaborate. Financial support is required for all of this.

I convinced my university last year that we need to do precision cosmology. The Royal Astronomical Society supported me afterwards. The group is made up of 20 people. We can ask Mexican researchers to come back to their home country and find a job. We have people from all over the world. It is exciting times.

When do you expect observations will start to disagree with general relativity?

We are close to that. I am certain that the recently launched James Webb Space Telescope will open a new door with observations closer to the origin of the universe. The first galaxies in the universe will be formed when hydrogen and helium are fused. I think general relativity won't work at that time because the energy is so high. The era can give you a very honest test about the theory of gravity.

I would put my money in the sky.

How does that differ from general relativity?

The space-time curvature is an important concept in general relativity. You can see the sun as a mass on a sheet, then it starts to curve. The basis of the universe was created by Einstein. The sun is forming a tornado. The sheet is twisted. This is called twisting.

Einstein used parallel gravity in his final calculations. Some people are writing mathematics. Einstein saw a way to connect his theory of general relativity with the force of electromagnetism. Maybe we can unify the forces. He wasn't successful, and his idea was forgotten.

Some theorists continued to work on it. A couple of years ago, Jackson Levi Said at the University of Malta found that it was possible to transform the language of teleparallel gravity into a cosmology, a set of equations that relate all the parameters that we observe in nature. This model could be connected to experiments. I will check it with the current data, for example, the Cosmic Microwave Background Radiation, which is light from the early universe. We found that the equations could match the data without using dark matter or dark energy.

What evidence is there for teleparallel gravity?

It is very elegant. teleparallel gravity is very similar to general relativity at a local level. There are differences in the very early universe and in the future.

teleparallel gravity will be the first test of the early universe. If we can explain the formation of the first galaxies better, that will be a great test. Maybe teleparallel gravity can explain what we see in the photos.

You mean the Event Horizon Telescope’s recent photographs of the supermassive black hole in the M87 galaxy. What’s puzzling about the photos?

The black hole has magnetic fields around it. The field lines are following the same flow. You can see what is happening inside the black hole with these magnetic field lines. A black hole absorbs matter that is near to it, so there is some matter inside the horizon and some outside, and the interaction causes the magnetic field. The magnetic fields are hard to understand.

One of the groups inside the Telescope Collaboration is looking for solutions. I am part of a group that is taking a different route with modifications and extensions of gravity.

We need more data to distinguish these possibilities. To see the evolution of the black hole, a movie is being planned. Maybe it will make it harder for us to test theories.

When you were a kid, did you ever imagine that you would end up challenging Einstein?

Challenging Einstein? Probably! This is the dream of any child that wants to understand the universe.

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