General relativity re-verified with higher precision

The only known pair of pulsars has just revealed a wealth of unique cosmic insights.

Scientists have been observing the pair of pulsars, or pulsating neutron stars, for 16 years. The measurements confirmed Einstein’s theory of gravity, known as general relativity, to a new level of precision, physicists said in a paper published Dec. 13 in Physical Review X, and hinted at the The subtle effects of theory.

Pulsars are spinning dead stars composed of dense neutrons that appear to flicker as their beacon-like beams of radiation regularly sweep across Earth. Variations in the timing of these pulses can reveal the motion of the pulsar and the effects of general relativity. While physicists have discovered many individual pulsars, this is the only pair known to orbit each other. In 2003, the discovery of the double pulsar system J0737-3039 opened up a possible new way to test the general theory of relativity.

One of the pulsars spins about 44 times a second, while the other spins about every 2.8 seconds. The slower pulsar dimmed in 2008 because of a strange phenomenon in general relativity that spun its beam out of view. The researchers will continue to monitor the remaining visible pulsars, then combine the new data with the old observations to improve the precision of the measurements.

Here are five takeaways from the new study:

  1. Einstein was right in many ways.

With this pair of pulsar binaries, we can simultaneously perform five independent tests of general relativity to check whether various properties of the orbits match the predictions of Einstein’s theory. For example, researchers measure the rate at which the orbit’s ellipse rotates, or precesses, to see if it is as expected. It turns out that all parameters are in accordance with Einstein’s theory.

What’s more, Scott Ransom, an astrophysicist at the National Radio Astronomy Observatory in Charlottesville, Virginia, said, “Each individual test of general relativity has become so precise that … it must include general relativity. The higher-order effects of relativity to match the data.” This means the measurements are so precise that they hint at the subtle properties of gravity.

  1. Gravitational waves are draining energy.

The observations show that the pulsar’s orbit is shrinking. By measuring the time it took for the pulsars to complete their orbits each time, the researchers determined that the pair of pulsars shortened by about 7 millimeters per day.

That’s because pulsars excite gravitational waves as they orbit, which are ripples in space-time that vibrate outward and carry energy away. This apparent contraction was first detected in a galaxy with a pulsar and a neutron star in the 1970s, providing early evidence for the existence of gravitational waves. But the new results are 25 times more precise than previous measurements.

  1. Pulsars are losing mass.

There is also a subtle effect that will change this track. The pulsar gradually slows down over time, losing rotational energy. Because energy and mass are two sides of the same coin, that means faster pulsars lose about 8 million tons of mass per second.

“When I first realized this, I was really stunned,” Kramer said. “While it sounds like a lot, the mass loss only affects tiny adjustments to the orbit. Previously, scientists could Ignore this effect, because the change is very small. But orbital measurements are now accurate enough that it makes sense to take it into account.

  1. We can know the direction of rotation of the pulsar, which hints at its origin.

By studying the timing of a pulsar as the light from a pulsar passes its companion star, scientists can tell which direction the faster pulsar is spinning. The results showed that the pulsar was spinning in the same direction as its orbit, providing clues to the formation of the pulsar binary.

The two pulsars began as neighboring stars exploded one after the other. Normally, when a star explodes, the remnants it leaves behind are washed away, breaking them apart. The faster pulsar spins in the same direction as its orbit, which means the explosion that formed the pulsar didn’t give it too much jolt, which helps explain how the binary system remains intact.

  1. We have a clue about the pulsar’s radius.

Gravitational effects are known to cause the orbit’s ellipse to precess, or rotate, about 17 degrees per year. But in the new study, a subtle tweak was involved. As the pulsar rotates, it acts like the twisting skirt of a whirling dancer, dragging the fabric of spacetime behind it, changing the precession.

This drag effect means that the faster pulsar must have a radius of less than 22 kilometers, an estimate that, if more precise in future work, could help reveal the origin of the extremely dense neutron star material that makes up the pulsar physical properties.


With a diameter of 250 million light-years, the interior is dark, how terrible is the Bode constellation?

We often say that the matter in the universe is uniformly distributed in all spaces after the big bang. With the passage of time, because of the imbalance between the expansion speed of the universe and the size relationship between celestial galaxies, its gravitational effect on matter is also unbalanced. It is different, so there are more blank spaces in the cosmic space.

But in general, the distribution of matter and galaxies in the cosmic space is relatively balanced, and there will be no particularly large deviations.

However, scientists have found a very large “hole” in the northeast direction of the Virgo galaxy in the northern sky. The hole is about 250 million light-years in diameter and about 700 million light-years away from Earth.

At this location, which is more than 2,500 times larger than the Milky Way’s 100,000 light-years, there are so few stars in it that it becomes a huge blank area, which scientists have named the “Boes Void”.

Boes Hollow
As one of the largest known voids in the universe, there are so few galaxies in the Boes Void that it is almost impossible to find a single galaxy until an average of 10 million light-years.

We can compare it like this: the diameter of the Milky Way is only about 1/2500 of that of the constellation Boe, and in terms of volume, the constellation Boo can hold tens of millions of galaxies. In this “small” Milky Way galaxy, there are 100-400 billion stars alone, but in this huge constellation Boes, scientists have discovered here in the more than ten years since its discovery in 1981 to 1997. The number of galaxies is less than 60. The gap is so large that Boes is sometimes referred to as the “super-void”.

According to the scientists’ calculation of the distribution of galaxies in other spaces, it is reasonable that there should be at least 2,000 galaxies in the constellation Boo, but the reality is quite rare, and the distances between them are quite far, on average, almost 2000 galaxies. 10 million light years. Why is the Shepherd’s seat so empty?

Because galaxies are too rare, there is a view that the original matter in the Boes constellation void may have been taken away by other surrounding matter with greater gravitational force in the early stage of its formation. Later, the universe expanded and the galaxies moved away faster than the speed of light. The Booness hole is naturally getting bigger and bigger.

From the distribution of some sparse galaxies, it has been suggested that the super-large void in Boes may be formed by the combination of multiple small voids. Others believe that the constellation of Boes is not empty and is filled with dark matter and dark energy.

The formation of cosmic voids
Scientists have discovered some (dark) blue regions from the microwave background radiation distribution map that studies the distribution of heat in the universe after the Big Bang. They are the “holes” of the energy-poor and extremely sparsely distributed universe.

There are not many “voids” in the universe, and Boes is just one of them. The largest cosmic void discovered by human beings is far more terrifying than the size of the constellation Shepherd. Its diameter can reach 1.8 billion light-years. It is simply an invincible giant, known as a “super void”.

These voids do not mean that they exist in a complete vacuum, but in terms of the total distribution of matter in the universe, the matter here is 20% or more less than that in other regions, and the density is extremely low. When there are voids in the universe, where no galaxies are found, there are naturally no stars, planets and other matter. Because no celestial body can exist independently of a galaxy.

That is, to some extent, we can understand the void of the universe as a dark region of “nothing”, including the Boes Void.

Maybe some people think that the gap between the galaxies is too big? Where did so many empty words come from?

According to scientists’ research on cosmic voids, about 10,000 galaxies have disappeared from the universe. The area where they were originally also lost energy due to the “invisibility” of matter, and gradually cooled to become the low temperature region of the universe. The blue part of the above-mentioned cosmic microwave background radiation map, the darker the color, the lower the temperature, there is almost no matter here.

But in this case, scientists also don’t know where these stars go, or why the galaxies are so far away from this area. It has been suggested that if dark matter is to be blamed, then the formation of voids may be related to the activity of dark matter.

So is there any other possibility besides dark matter? Some scientists have proposed another possibility: the expansion of advanced civilizations in the universe. How should this be understood?

What advanced civilization did?
Regarding the speculation and exploration of cosmic civilization, the world has never lacked reservations about advanced civilizations other than humans. After all, the universe currently has no boundaries for human beings, and it is not completely certain whether there will be civilizations that we do not know about.

According to the level of Kardashev civilization, civilization in the universe should have three major stages: planetary energy utilization, star system energy utilization, and (galaxy) parent galaxy energy utilization.

Based on this understanding, we can make a bold guess: Could the voids in the universe be caused by advanced civilizations that utilize the energy of other galaxies in the universe?

In order to better develop their own civilization, these advanced civilizations take, store, utilize and consume the energy of the galaxy, leaving only a void with nothing. When the energy of the nearby galaxy is completely absorbed, the advanced civilization will The range of galactic energy sources will continue to increase, and the voids will become larger and larger.

Such speculation is not completely unreasonable, but it is a bit exaggerated. The energy utilization of a star system is exaggerated enough. How advanced civilization must it consume tens of millions of galaxy energy? According to this consumption, how long will the galaxy energy in the universe be enough for these civilizations to consume?

Obviously, not many people agree with this view.

Other astronomers believe that these cold regions of space are evidence of cosmic cycles. It’s just that the theory of cosmic circulation is still in the stage of speculation and confirmation, and which view is more informative, we have to wait for more astronomical observations.

Do parallel universes exist? More than 80 years ago, a cat gave the answer

Whether it’s science fiction or science fiction movies, the coolest concept is traveling through time and space. Because based on common sense, everything is always developing towards the future, and no matter how fast or slow the passage of time, there is only one direction.

As sci-fi fans, many people dream of being able to travel through time and space, some hope to travel to the past, and some to the future.

The future is uncertain, and it is theoretically feasible to travel to the future. If we can drive a spacecraft to fly at a speed close to the speed of light, or orbit a black hole at a close distance, and by these two methods, we can delay the passage of time in our space-time region, and theoretically we can travel to the future.

The past has already happened, and if we can really travel to the past on the same timeline, then it is possible to change the present. The most famous is the grandmother paradox. If you go back to the past and accidentally harm your young grandmother, your father will not be born, so how did you come and travel back to the past to cause the accident? Wouldn’t that be a contradiction! The act of traveling back into the past breaks the law of causality.

However, parallel universes can solve this contradiction. According to the idea of ​​parallel universes, if you travel back in time and accidentally kill your young grandmother, that change will create a new branch of time, splitting off a parallel universe from that point in time. With the concept of a parallel universe, there is no need to worry about changing the past and affecting the future during the travel process, because this change will only generate new time branches, and the old timeline will not be affected.

According to this assumption, not long after the birth of the universe, there will be almost infinite parallel universes.

When it comes to parallel universes, the concept was born not from the time travel paradox, but from quantum mechanics. This goes back to a cat more than 80 years ago. The owner of this cat is the famous physicist Schrödinger, so this cat is also called “Schrödinger’s cat”.

Schrödinger, as the founder of wave mechanics in quantum mechanics, proposed the thought experiment “Schrödinger’s cat” in 1935. The purpose is to make people feel how weird the Copenhagen interpretation of quantum mechanics is, so as to attack the incompleteness of the Copenhagen interpretation.

The Copenhagen School believes that the quantum world is inherently uncertain, and that the properties of the system can only be described by probabilities, and the measurement behavior will have an impact on the system, and the set of probabilities is reduced to one of all possibilities. Scientists use wave functions to describe the properties of quantum systems, so this situation is also known as wave function collapse.

Schrödinger said that if a cat is kept in an airtight container containing a small amount of radium and the highly toxic cyanide, there is a chance that the radium decays and controls an electronic switch. If the radium decayed, it would trigger the mechanism to break the bottle containing the cyanide, and the cat would die; if the radium did not decay, the cat would still be alive.

According to quantum mechanics, radioactive radium is in a superposition of both decayed and non-decayed states. According to this principle, the cat in the airtight container should also be in a superimposed state of dead cat and live cat, which is the “Schrödinger’s cat” that is both dead and alive. The cat’s life and death status is determined only when we open the container.

For traditional physicists, this is inconceivable, and living and dying defies logic. They argue that the cat’s outcome is doomed before the container is opened: life or death. Just because the container wasn’t opened for observation, we’re not sure about the cat’s life or death.

It is well known that microscopic matter has wave-particle duality, and before observation, particle and wave properties are in a superposition state. According to the Copenhagen School of Quantum Mechanics, before opening the container, Schrödinger’s cat is in a state of superposition of life and death. Once the observation behavior is involved, this superposition state will be disturbed and manifested as one of the eigenstates.

This thought experiment cleverly moved the quantum phenomena in the microscopic world to the macroscopic world with a cat. It is one of the very classic thought experiments in the history of science. In fact, the reason for this bizarre result is that quantum superposition states are not suitable for macroscopic large objects.

Since the cat’s state of life is unknown before the container is opened, and there are two states, then perhaps there should also be two different worlds, one where the cat is alive and the other where the cat is dead . Based on this idea, the concept of parallel universes was derived.

In the 1950s, physicist Hugh Everett proposed the many-worlds interpretation of quantum mechanics and believed that there is no wave function collapse at all, and that cats and dead cats actually exist in two parallel universes.

According to this theory, everything that could have happened in the past and in the future either actually happened or will happen, but they all happened in other universes and have nothing to do with our universe. If there are really many parallel universes, then there must be another me in some parallel universes, but their lives are different.

All things have a beginning and an end. Physicists believe that there must be a proto-universe, and other parallel universes are constantly differentiated on this basis. These parallel universes coexist, and there will be no connection between the newly differentiated parallel universe and the original parallel universe, and they exist independently of each other.

Thinking about that cat gave birth to perhaps the most daring conjecture in the field of physics-parallel universe. Just for its existence, scientists can only discuss it from a theoretical level. However, there is a big problem with this theory. Will the universe really make such a big change for the life and death of a cat?