Physicists have long assumed that the universe is almost the same in any direction, and now they have found a new way to test the hypothesis: by examining the shadow of a black hole.
If the shadow is a little smaller than the existing physics theories predict, it may help to prove a distant concept, bumblebee. gravity, which describes what would happen if the seemingly perfect symmetry of the universe were not so perfect.
If scientists could find a black hole with such an undersized shadow, it would open the door to a brand new understanding of gravity – and perhaps explain why the universe is expanding ever faster.
But to understand how this bumblebee idea can fly, let’s look at some fundamental physics.
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Look in the mirror
Physicists love it symmetry; after all, it helps us to understand some of the deepest secrets of the universe. Physicists have realized, for example, that if you do an experiment on fundamental physics, you can move your testing equipment to another location and that you will get the same result again (that is, if all other factors such as the temperature and strength of gravity remain same).
No matter where your experiment is in space, you will get the same result. By means of mathematical logic it leads directly to the momentum conservation law.
Another example: if you run your experiment and wait a while before running it again, you will get the same result (again, everything is the same). This temporal symmetry leads directly to the law of conservation of energy – that energy can never be created or destroyed.
There is another important symmetry that forms a basis of modern physics. This is called the ‘Lorentz’ symmetry, in honor of Hendrik Lorentz, the physicist who invented it all in the early 1900s. It turns out that you can take your experiment and turn it around, and (even if it is equal), you will get the same result. You can also increase your experiment to a fixed speed and still get the same result.
In other words, all the others are equal – and yes, I repeat it often, because it’s important – if you do an experiment in total rest and do the same experiment at half the speed of light, you get the same result.
This is the symmetry that Lorentz has uncovered: the laws of physics are the same regardless of position, time, orientation, and speed.
What do we get out of this fundamental symmetry? Well, for starters we’ve got Einstein’s very special theory relativity, which sets out a constant speed of light and explains how space and time are linked for objects moving at different speeds.
Bumblebee gravity
Special relativity is so essential to physics that it is almost a meta-theory of physics: if you want to collect your own idea of how the universe works, it must be compatible with the precepts of special relativity.
Or not.
Physicists are constantly trying to accumulate new and improved physical theories, because the old, like general relativity, which describes how matter distorts space-time and the standard model of particle physics, cannot explain everything in the universe as it happens. in the heart of a black hole. And a very juicy place to look for new physics is to see if cherished concepts might not be as accurate in extreme conditions – cherished concepts like Lorentz symmetry.
Related: 8 ways you can see Einstein’s theory of relativity in real life
Some gravity models argue that the universe is not exactly symmetrical. These models predict that there are extra ingredients in the universe that force it to not always obey Lorentz symmetry. In other words, there would be a special or privileged direction in the cosmos.
These new models describe a hypothesis called “bumblebee gravity.” It gets its name because of the supposed idea that scientists once claimed that bumblebees would not be able to fly because we did not understand how their wings cause lift. (Scientists, by the way, never believed this.) We do not fully understand how these gravity models work and how they can be compatible with the universe we see, and yet, there they are, and we face viable options. for new physics.
One of the most powerful uses of drone gravity models is to explain it as possible. dark energy —The phenomenon responsible for the observed accelerated expansion of the universe. It seems that the extent to which our universe violates Lorentz symmetry can be linked to an effect that generates accelerated expansion. And because we have no idea what dark energy creates, this possibility indeed seems very appealing.
The black shadow
So you have a brand new theory of gravity based on some iconic ideas like violation of symmetry. Where would you test that idea? You would go to the place where gravity is stretched to the absolute limit: a black hole. In the new study, which has not yet been peer-reviewed and published online in the preprint database online in November 2020 arXiv, researchers just did it and looked at the shadow of a black hole in a hypothetical universe that is as realistic as possible.
(Remember that very first image of black hole M87, manufactured just a year ago by the Event Horizon Telescope? That ghostly beautiful, dark void in the middle of the bright ring was actually the “shadow” of the black hole, the region that sucked in all the light from behind and around it.)
To make the model as realistic as possible, the team placed a black hole in the background of a universe that accelerates in its expansion (exactly as we observe) and set the level of symmetry violation to the behavior of the dark energy that suits scientists. measure.
They found that, in this case, the shadow of a black hole could appear up to 10% smaller than it would appear in a ‘normal-gravity’ world, providing a clear way to test bumblebees. While the current image of the black hole M87 is too vague to discern the difference, efforts are underway to take even better photos of more black holes, exploring the deepest mysteries of the universe in the process.
Originally published on Live Science.