2021-10-09

Is there a parallel universe exactly like ours?

By yqqlm yqqlm

Assuming that there was a cosmic inflation before the big bang, in essence, all particles and fields in the universe have quantum properties. In this way, the existence of multiple universes is almost inevitable. This opens up infinite possibilities for physics. Perhaps there are not only parallel universes, but also infinite ones. In this way, there may even be a parallel universe exactly the same as ours. What might happen if multiple universes really exist

Is there a parallel universe exactly like ours?

during the inflation, the initial fluctuation level printed in the observable universe was about 0.003%, but it is these small defects that caused the temperature and density fluctuations in the cosmic microwave background and buried the seeds of today’s cosmic structure. These initial conditions cannot be explained without cosmic inflation

to understand why physicists believe that multiple universes should exist, we must first understand some facts we have observed in the universe. First, the universe we can reach has a time boundary. The universe we can observe was born in the big bang 13.8 billion years ago. At that time, the universe was extremely hot and dense, full of matter and radiation, and was expanding and cooling all the time. The farther we look back in space, the longer we look back in time, extending to the boundary of the Big Bang: 13.8 billion years ago in time and 46.1 billion light-years away in space

Is there a parallel universe exactly like ours?(1)

when the ball rolls to the bottom, the inflation will end (above). However, the inflation field has quantum properties (middle figure) and will expand over time. When inflation stops in many areas (purple, red and cyan), inflation in many spaces continues and may continue forever (below)

however, we cannot casually return to the early days of time, because if the universe at that time exceeded a certain temperature and density, it would produce some characteristics inconsistent with our observations. However, if the universe had experienced a period of inflation and made certain preparations before the big bang, the situation would be much more consistent with the observation results

inflation lengthens the curvature of the universe and makes the shape of the universe close to the plane. During the inflation process, all high-energy residues that may cause problems also expand. Through this process, the energy density everywhere in the universe becomes the same. Only some quantum fluctuations that occur during inflation are superimposed on this balanced energy background

Is there a parallel universe exactly like ours?(2)

as the inflation continues, a series of universes will be born one after another, each completely separated from other universes, and the distance will become farther and farther as the space between them expands further

in this way, when the cosmic inflation is coming to an end, the Big Bang has all the necessary characteristics to produce the observable universe today

we generally think of the expansion of the universe as a simple field. The specific properties of this field will affect the space where the field is located. As long as the field maintains the expansion state and the space has huge energy, the space will continue to expand endlessly and exponentially. Therefore, the distance between any two points will double every time period

as long as the field maintains this expansion state, the cosmic inflation will continue, continue to extend the space, and continuously dilute all the substances in it until the field decays, and the cosmic inflation will end. As energy is converted into matter and radiation, the universe will become more and more hot, marking the beginning of the big bang

Is there a parallel universe exactly like ours?(3)

schematic diagram of multiple parallel universes in multiple universes

but we know that no matter which field drives the cosmic inflation, it is likely to be quantum in nature. This means that as the cosmic inflation continues, this field may “roll off the cliff” and lead to the termination of inflation; This may not happen, and inflation can continue; It is even possible to “roll” in the wrong direction, leaving us farther and farther from the end of inflation. It is also counterintuitive that these situations may occur simultaneously in different regions of the universe because the inflating universe will continue to create new space

this creates a very interesting situation. As long as there has been cosmic inflation in the past (and from our observations, there is a lot of evidence that cosmic inflation has indeed occurred), it indicates that there are multiple universes. The process is as follows:

cosmic inflation occurs, and the universe is constantly elongated to produce new space; In some areas, the field will “roll off the cliff” to end the inflation, leading to a big explosion in these areas and the formation of what we call the “universe”; The space between these universes continues to swell, creating more space… And so on

it is easy to see that if we want the cosmic inflation to develop enough to make the big bang have the characteristics we observed, there will be multiple universes. New universes have been born continuously. These universes are independent and irrelevant to each other. Because the space between them has been expanding, new universes continue to appear and new big explosions continue to occur, the distance between these universes will be farther and farther. As long as this part of the theory is correct – and the evidence we have does show that it is correct – the most advanced scientific research has predicted the existence of multiple universes

Is there a parallel universe exactly like ours?(4)

the quantum fluctuations formed during inflation will stretch outward with the universe. When the inflation ends, these quantum fluctuations become density fluctuations and gradually evolve into the large-scale structure observed in the universe and the temperature fluctuations observed in the cosmic microwave background. These fluctuations are a random process, which means that if the total number of universes is limited and too small, there can be no two identical universes

are these universes interrelated

from here on, we will enter the field of speculation. We know that the energy scale at which the cosmic inflation occurs must be far lower than the Planck energy scale, otherwise we will observe some nonexistent signals in the universe. But we still lack some key information. For example, we don’t know when the cosmic inflation began, or even whether it has a starting point. Inflation may be the default state of the universe and will last forever. Our universe will not be born until the inflation in our region stops

Is there a parallel universe exactly like ours?(5)

the figure shows the application of the concept of parallel universe to “Schrodinger’s cat”. Although the idea of parallel universe is very interesting and fascinating, if there is no infinite space to accommodate all possibilities, inflation alone cannot create enough universes to include all the possibilities since the evolution of the universe for 13.8 billion years

we also do not know whether there is any entanglement between universes in multiple universes. We do not know whether these universes all follow the same physical laws and basic constants, nor whether there is a mechanism to dominate these laws and constants in the process of cosmic inflation or in the final transition before the big bang. In addition, we have no idea how to quantify the probability of these results. Cosmologists call it the “measurement problem”. According to our prediction, these universes exist, but we do not know how many such universes there are, whether they are related or in what way, or what similarities or differences they have with our universe

however, according to our measurement results in the universe and the calculation results based on the quantum properties of known particles and fields, although the physical laws and constants in different universes are the same, the specific initial conditions should be different

in our observable universe, the number of particles is limited, the time of interaction between particles is limited, and the possible results are limited. If there are infinite universes like us, at least one universe will contain all possible combinations of results

this means that the overall characteristics of each universe should be the same, because all universes originate from the same inflation field. Therefore, the average energy density, law, symmetry, conservation law, standard model, general relativity rule and many other characteristics of each universe should be the same. The biggest difference is the superposition of quantum fluctuations on this unified background. It is this small defect, which accounts for only one third of 30000, that provides the “seed” for the structure of our universe. This defect occurs randomly and spans all scales. There are countless possible results, and our universe should be only one of them

as long as the number of these universes is large enough, we should always produce a universe with exactly the same characteristics as our initial characteristics. You know, everything in our universe is limited, the number of particles is limited, the total energy is limited, the time of quantum interaction is limited, and the number of possible results is also limited. Although these figures are extremely large, they are not endless

but the number of universes born in the process of inflation is another matter. If inflation has been going on for a limited period of time, the number of universes will increase exponentially with the passage of time, but this number is limited after all; If the inflation has lasted for an infinite period of time, the number of universes must be infinite, and some universes must have experienced all possibilities

Is there a parallel universe exactly like ours?(6)

if the “bubble” eventually evolved into our universe collided with other universes in the early stage, it will leave “scars”. However, we have not found relevant evidence in our observations that different universes do not interact during inflation

isolated from each other? Or interaction

if the inflation has occurred for a limited time, we can conclude that according to the law of the growth of the number of universes and the law of the possible increase of the number of results in a single universe with time, there is no parallel universe exactly the same as ours in multiple universes. When we use multiple worlds