What are dark matter and dark energy?
economist.com
economist.com
无论是暗物质还是暗能量，它们都是现在物理学的未解之谜。要理解黑暗宇宙的真正本质，科学家们可能需要重新评估对引力的认识。当科学家们试图理解暗能量和暗物质时，很有可能我们的引力基本理论是错误的，广义相对论也不是完全正确的。
One newly discovered dwarf galaxy located a mere 94 million light-years away is defying expectations. It's named FAST J0139+4328, and it's not emitting any optical light.
sciencealert.com
sciencealert.com
In 2018, astronomers discovered one large galaxy, NGC 1052-DF2, mysteriously possessed several hundred times less dark matter than expected from the conventional theory of galaxy formation.
Then, in 2019, they discovered another large galaxy, NGC 1052-DF4, that was similarly devoid of dark matter.
Galaxies shouldn’t be able to form without dark matter, but with the help of ancient collisions, these seemingly impossible objects were able to emerge.
Dwarf galaxies are small galaxies that contain anywhere from 100 million to a few billion stars. In contrast, the Milky Way has 200 billion to 400 billion stars.
While all UDGs are dwarf galaxies, all dwarf galaxies are not UDGs. A UDG has the stellar content of a dwarf galaxy, 10-100 times smaller than the Milky Way. But its size is comparable to the Milky Way, giving it the extremely low surface brightness that makes it special.
“Some people confuse agnosticism (not knowing) with apathy (not caring).”
“Doubt is not a pleasant condition,” Voltaire said, “but certainty is an absurd one.”
“Le doute n'est pas une condition agréable, mais la certitude est absurde.”
“Le doute n'est pas une condition agréable, mais la certitude est absurde.”
Quantum mechanics has predicted countless experiments, spawned countless applications. The trouble is, physicists and philosophers disagree over what it means, that is, what it says about how the world works.
Quantum mechanics defies common sense. For more than a century, physicists have tried to interpret the theory, to turn it into a coherent story, in vain.
“Physicists have more in common than most would like to admit with artists, who try to turn the chaos of things into a meaningful narrative.”
“The laws of quantum mechanics are confusing, predicting that particles are also waves and that cats are simultaneously alive and dead. However, one of the most confusing of all quantum principles is called the Heisenberg Uncertainty Principle.”
The effects of vacuum energy can be experimentally observed in various phenomena such as spontaneous emission, the Casimir effect and the Lamb shift, and are thought to influence the behavior of the Universe on cosmological scales.
"The 'bubbles' in the quantum foam are quadrillions of times smaller than atomic nuclei and last for infinitesimal fractions of a second — or in 'quantum-speak', the size of a Planck Length for a Planck Time," says physicist Eric Perlman.
A possible way to test for the presence of quantum foam is to measure how long it takes photons erupting from stellar explosions to travel great distances.
If spacetime is flat and boring, two photons ejected from the same source should take the same time to travel a set distance. But if spacetime is foamy, then one photon might get slowed by the slight perturbations.
The vast majority of electromagnetic waves that come from the sun are invisible to us. The most high-frequency waves emitted by the sun are gamma rays, X-rays, and ultraviolet radiation (UV rays).
One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood.
A study made headlines claiming that the mysterious “dark energy” cosmologists believe is accelerating the expansion of the universe could arise from supermassive black holes at the hearts of galaxies.
science.org
science.org
At first blush, black holes and dark energy seem to have nothing to do with each other.
According to general relativity, a black hole is a pure gravitational field so strong that its own energy sustains its existence.
According to general relativity, a black hole is a pure gravitational field so strong that its own energy sustains its existence.
“Most new theoretical ideas are dismissed by skepticism. But if we dismiss all the new ideas then there won’t be anything left.”
For their latest magic trick, physicists have done the quantum equivalent of conjuring energy out of thin air. It’s a feat that seems to fly in the face of physical law and common sense.
quantamagazine.org
quantamagazine.org
The trouble arises from the bizarre nature of the quantum vacuum, which is a peculiar type of nothing that comes dangerously close to resembling a something.
We’ve established that the Higgs boson is a spin-zero, a.k.a. “scalar” particle, but what does that mean? And what does that have to do with the Higgs field? symmetrymagazine.org
Will the universe end in a bang or a whimper? A pair of theoretical physicists have proposed a third path: perhaps the universe will never end.
livescience.com
livescience.com
Cosmologists do not understand the cause of this acceleration, which they name dark energy. If this acceleration persists, then our universe will eventually expand into oblivion, with all matter and radiation torn apart.
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