The birth of the universe
13.7 billion years ago, after a big bang, the universe appeared, and this is the starting point of everything.
All kinds of dust and elementary particles began to fuse, and gradually there were stars, planets, and nebulae. All of this builds the universe as we know it, and according to existing physical theories, the fastest matter in the universe is light, and no object can move beyond the speed of light.
The Big Bang was the starting point for the universe to appear
At the same time, the research of modern scientists has also confirmed that the universe is constantly expanding, the speed is exaggerated, the entire universe is accelerating and expanding at a state of faster than the speed of light, and the scale of the observable universe has reached 46 billion light years.
So will you have a strange doubt born in your heart? Since objects cannot move faster than the speed of light, and the universe is only more than ten billion years old, why can it expand faster than the speed of light, and the observable scale is still increasing? Does this violate the laws of physics, or even contradict existing theories?
A universe expanding faster than the speed of light
Before questioning, let's first look at the physical systems and theories related to this universe, and then use a ruler to make a detailed figurative explanation, and you will understand. You read that right, just a ruler can understand this complex concept, but only if it is based on the premise of basic cognition.
Know the universe
The first thing that is certain is that the universe is indeed expanding faster than the speed of light, and this state of expansion is still accelerating. The universe also experienced a major inflation in the early days, and the inflation of this period was even more exaggerated. Inflation occurred 10−36 seconds after the Big Bang, and between 10−33 and 10−32 seconds, the universe expanded instantaneously from the size of an atomic nucleus to the size of the solar system.
The expansion of the universe is accelerating
Even light cannot reach this speed, and for such a tiny moment, light can only pass through one billionth of the diameter of an atomic nucleus. After the great inflation, the expansion rate of the universe slowed down a little.
Scientists may start with electromagnetic mechanics, and early scientists have been in a tangled state of entanglement over electricity and magnetism. To describe the relationship between magnetic fields and electricity, they had to look for an equation that would explain the problems of these related phenomena.
The relationship between the universe and electromagnetic mechanics
After the efforts of many scientists, all the way to Maxwell's place, the problem of electromagnetic field force has been basically solved. Among them, Maxwell's four key equations are composed of the key to solving the electromagnetic field problem.
In addition to the changes in electromagnetic mechanics, there are uncontrollable contradictions in the study of electromagnetic mechanics according to the classical physical system established by Newton. If you want to get the right answer, you must have a new theoretical system.
Maxwell's theory of electromagnetic fields
To solve this problem, Lorentz established a conversion relationship in which the observer measures physical quantities between different inertial frames of reference. This is the famous Lorentz transform, and after solving this problem, the emergence of Einstein raised modern physics to a higher level, and the theory of relativity appeared.
The Lorentz transform and Maxwell's equations make up the basic equations of relativity, and after general relativity, there is a preliminary way to observe the universe, measuring the universe through the establishment of mathematical models.
Lorentz transform
So, how to use this knowledge to solve the problem that objects cannot exceed the speed of light? After explaining the theory of relativity, Einstein gave the answer in his own subsequent study using the Lorentz transform's velocity synthesis formula.
The formula also introduces the effect of space-time expansion caused by changes in velocity, and after solving the equations, the theory is derived that objects will only be infinitely close to the speed of light, or even reach the speed of light, let alone exceed the speed of light.
Space-time expansion effect
Relativity reveals the relationship between matter and space-time, their state of motion. This is fully reflected in today's satellites, and even the most accurate atomic clocks will have time deviations. The motion of objects is not absolutely variable, and this relativization gives us a basic premise for understanding the expansion of the universe.
As far as the universe itself is concerned, space-time itself also needs to move, and the universe cannot remain stationary, so continuous expansion is the true state of the universe. The relative state of motion depends on the observer's frame of reference.
Einstein's relativistic view of space-time
It's like a particularly fast car that can circle the earth at great speed, and this car is like the light emitted by the sun, and the sun itself rotates more than the distance the photons need to escape, but you can't say that the sun is faster than the speed of light. Similarly, the car will never see its taillights.
The speed of movement of the object is also related to the mass, in the same linear motion state, how much is the relative speed of the object, this part of the mass will be increased under the blessing of speed, to be precise, there will be greater energy.
Photons are an energy in themselves
When the speed of motion reaches its mass limit, the speed will appear to be flattened, and in order to exceed the speed of light, the mass must be infinitely close to zero. However, objects without mass cannot move, which limits any object to moving beyond the speed of light.
So at present, faster-than-light spacecraft can only exist in the imagination
The photon itself is an energy, and the way it moves is essentially the speed of light itself, so it cannot be surpassed by itself or surpassed by itself.
Observe the changes
After understanding the relevant knowledge, we return to the matter itself, why the expansion of the universe can exceed the speed of light.
Faster than the speed of light
In fact, the motion of the universe is not as simple as we think, and the expanding universe does not contain faster-than-light motion, but is more of a spatial change. In special relativity, an object with static mass cannot reach the speed of light, but in general relativity, an observer can only measure the physical quantities of its neighbors.
outer space
That is to say, the universe we know is not a static space on the entire macroscopic scale, and every place can move and change, and our observations are limited, resulting in the limitation of observations. Therefore, for the observer, the adjacent region does not belong to the same reference frame, and the mass particles that pass through its region cannot reach the speed of light.
What is in the universe is not temporary
The expansion of space itself is not subject to this restriction, and is not limited by the speed of light, because it is different from the simple movement of the speed of light and is not restricted. To give an inappropriate example, you are now on a straight road with a flag 200 meters from you, and this flag is the end.
From the beginning of your running, the road is constantly being stretched, when you first start running, you may run through a section of the road, but soon you will find that the road behind you is also constantly stretching, and the whole road is getting longer and longer, and then your whole person looks like it is stationary, but in fact you are really running desperately.
Use the ruler as an expander
Just like the ruler on the ruler, the distance between each scale is elongated and changed, and the original 1 meter ruler changed from 1 meter to 100 meters in less than 1 second, but its measurement range is still within 1 meter.
The difference is that the distance between all scales on the ruler has changed from the original 1 centimeter to 1 meter. The scales between the adjacent sides are 1 meter away from the left and right sides. The regressive change between scales becomes an intuitive feeling of the expansion of the ruler.
Expanded ruler
This state of the ruler scale is presented, in the process of movement, the relative speed is doubled, and the distance increased by the increase of the relative speed is the carrier of the uniform expansion of the object.
Returning to the observation of the universe, the changes between galaxies and galaxies are like changes in the scale on the ruler, and this faster-than-light regression is based on the premise that the Milky Way is used as a reference system. So in essence, the distance between them is constantly being stretched, not moving at the speed of light.
Binary Mouse Galaxy
As an observer, even if you stand still, you can feel this feeling of being stretched, which is the same as running on the track that can be stretched as listed earlier. After realizing all this, you will understand why the universe can expand at a faster speed than light, but no object can move faster than the speed of light, because the two are actually strictly different in nature.
Where does the future go?
Since the expansion of the universe is so weird, scientists have to seek a reasonable explanation, in order to fill this gap, the emergence of the dark energy hypothesis, which explains that the universe is accelerating expansion.
Dark energy and light will neutralize
The expansion of the universe was proposed in the 19th century, but in the billions of years since the birth of the universe, has it accelerated or slowed down? This judgment is mainly based on the measurement of celestial distances and redshift relationships in the universe.
By inferring the distance by the brightness change and position change of the star, of course, this is not to take a star as the basis for observation, but to choose a celestial body with absolute brightness as the standard. Only supernovae after the evolutionary explosion of massive stars have this ability, and their bursts can be brighter than the entire galaxy, even if they are far apart.
Stars undergo nuclear fusion in their cores
And the redshift is like a spot on a balloon, the universe is this balloon, as the balloon gets bigger and bigger, the distance between the spots will become farther and farther. The energy that makes the universe expand comes from this dark energy, which occupies 70% of the space in the universe.
Through neutrino oscillations and changes in microwave background radiation, scientists were able to track the subtlest changes in the universe. The result of the observation is that the universe is indeed expanding at an accelerated rate. Cosmic changes dominated by dark energy will determine the fate of the universe in the distant future.
Neutrino astrophysics
This accelerated expansion worries some scientists that if the expansion continues, the matter and energy in the universe will become thinner and thinner. Galaxies moving away from each other can become so fast that no new structures will form.
Einstein's general theory of relativity was questioned incorrectly, because at that time Einstein hypothesized that if the universe was to remain stationary, it was necessary to add a constant, which is now called the cosmic constant.
Einstein's cosmological constant
After adding the cosmological constant, space-time stopped the tensile change and began to shrink back again. Based on the space-time model established by the theory of relativity, we can assume that more and more matter is distributed around space-time, the curvature of space-time begins to become apparent, and space begins to expand.
In the second half of the relativistic equation, if this cosmological constant is added, the region of space-time flattens and begins to contract. Einstein used this method to make the universe "calm". But it was soon questioned by other scientists because the universe expands in redshift observations of celestial bodies.
Three redshifts of light
Regarding the assumption of the cosmological constant, Einstein was quick to admit his mistake. Interestingly, though, more than 100 years later, observational equipment is constantly being upgraded as theoretical physics continues to improve. Scientists speculate that the cosmological constant exists, but perhaps in negative form, and that the universe is expanding faster than anyone can imagine, and the original erroneous reasoning has returned to the temple of science.
Dark energy is thought to be the embodiment of the cosmic constant
Today, scientists are still constantly exploring and revealing this secret dark energy, hoping to get more mysteries about the universe from it. For the study of dark energy, not only Japan, the United States and other regions, including the mainland will invest a lot of energy to prepare.
The continental space station sky survey and the Tianlai plan are all prepared for this purpose, including some international cooperation projects, which are ready to reveal the real reasons behind the accelerated expansion of the universe. At the same time, with the discovery of neutrino oscillations, the mystery of dark energy is also being unveiled little by little.
Powerful cosmic dark energy
The next few years will be the golden age of dark energy research, and with the joint efforts of scientists around the world, the expansion of the universe will surely get a clearer and more accurate understanding.