Many people have likely heard of the concept of the multiverse, but often regard it as merely a theme in science fiction movies, far removed from our real world. In fact, the multiverse is not just an illusion; some scientists have even uncovered evidence suggesting that our universe may be part of a multiverse.
A study published by Cornell University on May 9, 2023, claims that in experiments involving ferromagnetic liquids, they discovered that the multiverse predicted by eternal inflation theory could actually be real.
Surprisingly, this experiment is not the only evidence supporting the existence of a multiverse, as many other studies have indicated similar findings. A 2017 study from Durham University in the UK pointed out that in the cosmic microwave background radiation (CMB) produced by the Big Bang, we have observed several particularly cold regions, especially large circular “cold spots”, which may originate from other universes formed close to ours. These universes could have had gravitational interactions with our universe during the Big Bang, leaving behind these traces.
The multiverse predicted by eternal inflation theory could actually be real.
You might be wondering, what exactly is the multiverse? The multiverse arises from the eternal inflation model. This aligns with predictions from quantum field theory, making it more plausible and 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 from an extremely dense and minuscule singularity, and there remains no clear answer as to why this singularity exploded and how energy was generated in the universe.
Thus, in 1981, the theory of cosmic inflation was proposed to address these issues. According to the inflation theory, the universe underwent exponential expansion for a period from 10^-36 seconds to 10^-32 seconds after its birth. During this incredibly brief period, the volume of the universe increased nearly 10^78 times from its initial state of zero. This means that the universe expanded from an initial zero volume to the size of the universe we observe today, or even larger.
Why does cosmic expansion occur? The reason lies in the early state of the universe, where a inflationary field existed as a scalar field in space. This can be viewed as dark energy, with the vacuum at this time filled with immense energy, thus referred to as a false vacuum. Between 10^-36 seconds and 10^-32 seconds, the vacuum energy caused the expansion of space. When the expansion ceased, the vacuum energy decayed and produced matter. This phase marks the heating up of the universe, the beginning of what we call the Big Bang.
The multiverse arises from the eternal inflation model.
After the vacuum energy was released, the rate of expansion of the universe slowed significantly, but the universe continued to expand because some of the energy in the inflationary field remained in the vacuum, which we now refer to as dark energy.
Dark energy continues to drive the expansion of space. With inflation theory, we can understand the origin of the thermal state of the Big Bang, stemming from the decay of vacuum energy. Although we currently do not know what happened in the timeframe from 0 to 10^-36 seconds, the emergence of inflation theory has made the Big Bang model more complete.
However, in 1986, Alan Guth’s inflation theory was further developed by three physicists into the eternal inflation theory. Based on this theory, we can make the following predictions: “The expansion of the universe has not stopped and continues. New space is created with the same amount of vacuum energy. When expansion halts somewhere in space, bubble regions will form. These bubble areas have undergone a big bang, creating a bubble universe. Our universe is one of many bubble universes.”
As time passes, the universe will create many bubble universes, which is the multiverse.
To understand the eternal inflation model, imagine a small ball rolling down a gentle slope. The bottom of the slope is a valley, and the ball on the slope has a certain potential energy. This state can be likened to the universe filled with vacuum energy, which is a false vacuum.
Clearly, the ball is not in a stable state; over time, it will eventually roll down into the valley, releasing energy and moving into a stable state. This marks the end of expansion.
When the vacuum releases energy, it creates other particles and fields, resulting in the hot big bang. If the inflationary field in the vacuum were classical, the problem would be relatively simple, as we could determine when the ball would roll down the slope. Once it entirely rolls down, the expansion would cease, and the universe could only form one universe.
However, the inflationary field is a quantum field, and the ball is not a macroscopic object but is governed by quantum mechanics. Thus, the timing of when the ball rolls down the slope is uncertain, and it will oscillate up and down the slope. Therefore, in different expanding regions of the universe, the moment of expansion’s end will also differ. In some spaces, a universe can be formed quickly, while in others, it may take much longer. As time passes, the universe will create many such bubble universes, which is the multiverse.
We cannot communicate with other universes.
So, can we communicate with other universes? Clearly, this is impossible. As the space in each universe is expanding much faster than the speed of light, no information can be exchanged in any form between the two universes. Therefore, to prove the existence of a multiverse, we can only seek indirect evidence.
According to some scientists, when the multiverse is created, the universes are very close together. This leads to gravitational interactions that leave cold spots in the cosmic microwave background radiation. We know that cold spots result from strong gravitational forces. Thus, research published in the journals Physical Review Letters and Physical Review D has detected cold spots in the cosmic microwave background, possibly caused by nearby other universes.
However, in the international scientific community, there is no consensus on this issue. Most scientists believe that these cold spots are traces of the gravitational influence of ancient superclusters, not evidence of a multiverse.
So how can we prove the existence of a multiverse? One way to demonstrate this is by creating a quantum multiverse on Earth by harnessing quantum phenomena to recreate inflationary field behavior. As long as the quantum phenomena we observe in the laboratory align with our predictions about this quantum ball, it means that the original inflationary field has the potential to develop as we predicted.
To prove the existence of the multiverse, we can only search for indirect evidence.
Cornell University has published a study that represents the first experimental evidence supporting the existence of the multiverse. The experiment was conducted on May 9, 2023, using ferromagnetic liquids as the subject of study.
When these liquids transition from a supercooled state to a ground state, similar to a ball rolling down a slope, they behave very much like the decay process of an inflationary field. This generally aligns with the predictions of eternal inflation theory, but this experiment is linear and one-dimensional. To prove the existence of a multiverse, we still need to conduct two-dimensional and three-dimensional experiments. Therefore, scientists are pursuing additional experiments.
In quantum physics, when atoms reach extremely low pressures and temperatures, the wave function of the atoms develops a combination, and all atoms exist in the lowest and identical quantum state. This phenomenon is known as Bose-Einstein condensation. Researchers have also observed the formation of tiny vacuum bubbles within these condensate clouds.
From a data perspective, these ultra-small vacuum bubbles are analogous to creating cosmic bubbles. Scientists are currently conducting similar experiments using potassium atoms and plan to publish their results next year. Therefore, the multiverse is indeed plausible because it makes logical sense.
