How do scientists prove the existence of the multiverse?

Surely many people have heard of the concept of multiverse, but many people only consider it a concept in science fiction movies, far from our real world. In fact, multiverse is not just an illusion, some scientists have even found evidence that our world is multiverse.

A study published by Cornell University on May 9, 2023, claims that in experiments on ferromagnetic fluids, they discovered that the multiverse predicted by the theory of eternal expansion may be real. 

Surprisingly, this experiment is not the only evidence for the existence of the multiverse, as many other studies have pointed to this as well. A 2017 study from Durham University in the UK found that in the cosmic microwave background (CMB) radiation produced by the Big Bang, we have observed some particularly cold regions, specifically giant circular 'cold spots,' that may have come from other universes and formed near our own. These universes may have gravitationally interacted with our universe during the Big Bang, leaving these traces behind.

 The multiverse predicted by the theory of eternal expansion may be real.

You may be wondering what exactly is a multiverse? The multiverse comes from the eternal expansion model . It fits the predictions of quantum field theory, is more logical, and is directly related to the Big Bang model of the universe.

According to the Big Bang theory, our universe was formed 13.8 billion years ago in an extremely dense and extremely small singularity, and there is still no clear answer as to why this singularity exploded and how the energy in the universe was created.

So in 1981, the inflationary theory of the universe was proposed to solve the above problems. According to the inflationary theory, the universe underwent an exponential expansion between 10-36 seconds and 10-32 seconds after its birth. During this very short period of time, the volume of the universe increased by almost 1078 times from its initial zero. That is, the volume of the universe expanded from its initial zero to the size of the universe we observe or even larger.

Why does the expansion of the universe occur? The reason is that in the early stages of the universe, there was an expansion field in the form of a scalar field in space. It can be considered as dark energy , the vacuum at this time was filled with enormous energy so this vacuum is called a false vacuum. Between 10-36 seconds and 10-32 seconds, the vacuum energy caused the expansion of space. When the expansion stopped, the vacuum energy decayed and created matter. This stage is the heating stage of the universe, the beginning of what we call the Big Bang.

The multiverse comes from the eternal expansion model.

After the vacuum energy was released, the expansion rate of the universe slowed down significantly, but the universe continued to expand because some of the energy in the expansion field remained in the vacuum, which is what we now call dark energy.

Dark energy is still causing space to expand. With inflation theory, we can understand the origin of the thermal state of the Big Bang, which came from the decay of vacuum energy. Although we currently do not know what happened between 0 and 10-36 seconds, the advent of inflation theory has made the Big Bang model more complete.

However, in 1986, Alan Guth's inflation theory was developed by three physicists into the theory of eternal inflation. Based on this theory, we have the following prediction: "The expansion of the universe has not stopped but is still continuing. The newly created space has the same amount of vacuum energy. When the expansion stops somewhere in space, a bubble region will form. This bubble region has undergone a big bang and a bubble universe has been born . The universe we live in is one of many bubble universes."

 As time passes, the universe will give birth to many bubble universes, which is the multiverse.

To understand the eternal expansion model, imagine a small ball rolling down a gentle hill. The bottom of the hill is a valley, the ball on the hillside has a certain potential energy. This state can be compared to the universe being filled with vacuum energy, which is a false vacuum.

Obviously, the ball is not in a stable state, as time passes, it will eventually roll down the valley, releasing energy, entering a stable state. This represents the end of expansion.

As the vacuum releases energy, it creates other particles and fields, creating a hot big bang. If the expansion field in the vacuum were classical, the problem would be relatively simple, since we could determine when the ball would roll down the hill. Once it had completely rolled down, the expansion would stop and the universe could only form one universe.

However, the expansion field is a quantum field and the ball is not a macroscopic object but is controlled by quantum mechanics. So the time when the ball rolls down the hill is uncertain and it will oscillate up and down the hill. So in different regions of the expanding universe, the time when the expansion ends is also different. In some spaces, the universe can be born quickly, while in other spaces it can take a long time. As time goes by, the universe will give birth to many such bubble universes, that is the multiverse .

We cannot communicate with other universes.

So can we communicate with other universes? Obviously this is impossible . Since space within each universe is expanding much faster than the speed of light, no information can be exchanged in any form between the two universes. So to prove the existence of the multiverse, we can only look for indirect evidence.

According to some scientists, when the multiverse was created, the universes were very close to each other. This created gravitational interactions that left cold spots in the cosmic microwave background radiation. We know that cold spots are the result of strong gravity. So, according to research papers published in the journals Physical Review Letters and Physical Review D , cold spots have been detected in the cosmic microwave background, which may be caused by other universes nearby.

However, there is no consensus in the international scientific community on this issue. Most scientists believe that these cold spots are traces of the gravity of ancient superclusters, not evidence of a multiverse.

So how do we prove the existence of a multiverse? One way to do so is to create a quantum multiverse on Earth by exploiting quantum phenomena to reproduce the behavior of the expansion field. As long as the quantum phenomena we observe in the laboratory match our predictions about this quantum sphere, it means that the initial expansion field is likely to evolve according to our predictions.

To prove the existence of the multiverse, we can only look for indirect evidence.

Cornell University has published a study that is the first experimental result to prove the existence of a multiverse. The experiment was conducted on May 9, 2023 and used ferrofluid as the research subject.

As these fluids transition from their metastable state to their ground state, like a ball rolling down a hill, they behave very much like the decay of the expansion field. This is broadly consistent with the predictions of eternal inflation theory, but the experiment is linear and one-dimensional. If we want to prove the existence of the multiverse, we still need to conduct two- and three-dimensional experiments. So scientists are working on other experiments.

In quantum physics, when atoms reach extremely low pressures and temperatures, the wave functions of the atoms become coherent and all the atoms are in the same, lowest quantum state. This phenomenon is called Bose-Einstein condensation. Researchers have also observed the formation of tiny vacuum bubbles within these condensation clouds.

From a data standpoint, these microscopic vacuum bubbles are similar to the creation of cosmic bubbles. Scientists are currently conducting similar experiments using potassium atoms and plan to publish their results next year. So the multiverse is very likely because it makes logical sense.