The most common image we have of the Big Bang is that at some point an expanding universe emerged.

But what if this universe is the twin of another universe that formed simultaneously at that point and expanded in the opposite direction?

Bold proposal recently published by a group of cosmologists at the Perimeter Institute for Theoretical Physics in Canada.

And they go further.

In this counter-universe they propose, time moves in the opposite direction as ours moves in the opposite direction.

As complex as it may seem, this hypothesis is an attempt by its authors to explain the various mysteries of the cosmos, including the mysterious dark matter, in a simpler and more “economical” way.

on the other side of the mirror

There are two key concepts to understanding the idea of ​​an anti-universe.

The first has to do with the Standard Model of particle physics, the theory that describes the fundamental particles from which the universe is made and the forces that make them interact with each other.

According to the Standard Model, whenever a matter particle appears, its antimatter counterpart also appears, the same particle but with a different charge.

This means that the same amount of matter and antimatter were produced during the Big Bang.

The second concept is symmetry.

In cosmology, this principle states that any physical process remains the same even if time goes back, space reverses, or particles are replaced by antiparticles.

Based on these two principles, the analogy might be expected to be an anti-universe symmetrical to what we know, just as there is a universe.

Symmetry

In a recent study from the Institute for Environmental Theoretical Physics, the authors analyzed a type of symmetry called CPT, initials of charge, parity, and time.

This symmetry indicates that if you reverse the charges, appearance, and time of a particle interaction, that interaction will behave in the same way.

Therefore, according to the authors of the study, this symmetry that applies to particles can also be applied to the universe as a whole, thus opening up the possibility of a symmetrical universe.

“The universe as a whole is CPT symmetric,” the authors write in their research.

Under this premise, the Big Bang is the starting point from which the universe and its mirror image emerged.

“We propose that the universe before the Big Bang is the ‘opposite’ of the universe after the Big Bang.

How is that anti-universe?

Latham Boyle, one of the study’s co-authors, warns that he is unsure of the anti-universe hypothesis and that his suggestions need to be empirically confirmed.

But he thinks his accounts give him some clues.

“So far we believe that the counter-universe is a true mirror image, reflected in time as particles and antiparticles are exchanged,” Boyle says in a conversation with BBC Mundo.

According to this view, this antiuniverse is not an independent universe, but merely a reflection of our universe.

“We have an ‘anti-self’ in the other universe, but it is not independent,” Boyle says.

“If you choose to eat eggs for breakfast, your opposing version cannot choose to eat bacon for breakfast.”

“If you have eggs for breakfast, it should be anti-eggs for breakfast.”

What about the time on the antiverse?

As Boyle and colleagues suggest, the Big Bang is like a mirror that reverses not only the image but also the direction of time.

On both sides of the universe, time moves away from the Big Bang, with only the arrow of time going right on one side and left on the other.

“Every part of the universe thinks this is perfectly normal,” Boyle says. “Both believe their time is moving forward.”

“From our point of view, time goes back in the opposite universe, but for them it’s us who go backwards.”

Boyle’s idea holds another surprising possibility: Maybe we are the anti-universe and we don’t know it.

And another question you can ask yourself: Is it possible to travel to that anti-universe?

“We can’t get to the other side of the mirror,” Boyle says. “It must be possible to travel to the past for this.”

That is, you have to travel through space-time, cross the Big Bang singularity, and exit the other side.

minimalist solutions

But beyond these sci-fi-like ideas, Boyle and colleagues’ work also proposes solutions to more practical problems in physics and cosmology.

His proposal offers compelling insights into three fundamental concepts of cosmology: dark matter, post-Big Bang inflation, and gravitational waves.

Dark matter is a mysterious component that makes up 25% of the universe, but until now no one has been able to observe what it is or what it is made of.

But dark matter can be noticed because of the gravitational effect it exerts on the cosmos.

For years, scientists have proposed various theories to explain what dark matter is, but no one has a convincing answer yet.

Some of the possible answers suggest that dark matter consists of a particle we don’t know yet, namely outside the Standard Model.

But Boyle’s work offers a “cheaper” answer to the dark matter puzzle.

His suggestion is that it is not necessary to imagine new particles to explain dark matter.

Instead, Boyle thinks the answer might be that dark matter is made of “right-handed neutrinos,” a variety of neutrinos, a class of particles that are indeed part of the Standard Model.

“Right-handed neutrinos” have yet to be proven, but according to Boyle, most scientists agree that they may be part of the Standard Model.

Thus, Boyle avoids the trouble of speculating with new particles and finds the answer in the laws of physics we already know.

Until now, known neutrinos are “left-handed”, referring to the direction in which they spin.

But in a symmetrical universe, one would expect a right-handed neutrino, namely an antineutrino, according to astrophysicist Paul Sutter in an article on the Live Science portal in which Boyle reviewed his work.

These right-handed neutrinos would be mostly invisible and their presence could only be detected by gravity.

“An invisible particle that covers the universe and interacts only through gravity is very similar to dark matter,” explains Sutter.

Physicist Joseph Formaggio, who studies the role of neutrinos in cosmology, says he finds Boyle’s proposal to explain dark matter interesting.

“I like the minimalist model,” Formaggio, who was not involved in the investigation, tells BBC Mundo.

“Usually in particle physics you can explain many phenomena by introducing new particles, interactions, and fields, so it’s easy to get lost.”

“But this research has another approach, it doesn’t add anything beyond what we’ve observed before,” concludes Formaggio, head of the Department of Experimental Nuclear and Particle Physics at the Massachusetts Institute of Technology.

Formaggio refers to the fact that the idea is very common, although it is not known whether right-handed neutrinos exist.

“They’re a new particle, but they’re not actually,” he says with a laugh.

Neither inflation nor gravitational waves

Finally, the study questions the existence of cosmological inflation and primitive gravitational waves.

Boyle’s model questions whether there was a period when the universe expanded rapidly after the Big Bang, a concept known as inflation.

This swelling may have created primitive gravitational waves, which are waves that move through the fabric of space-time like waves from a stone thrown into a lake.

Boyle’s proposal suggests that matter in the universe expands less forcefully, rather than inflating, without the need for an “age of inflammation.”

So, according to this model, if there were no swelling, there would be no primitive gravitational waves.

Gravitational waves were detected for the first time in 2015, but Boyle warns that these correspond to events much later than the Big Bang and are therefore not primitive gravitational waves.