Post by Eugene 2.0 on Feb 1, 2021 20:14:09 GMT
Gravitation Waves Will Prove Theory of Relativity is Wrong
Over the past five years, humanity has begun to practice a wholly new type of astronomy: gravitational wave astronomy. Instead of looking at some form of light coming from the Universe — gathered with a telescope, radio dish, antenna, or some other equipment sensitive to electromagnetic radiation — we’ve instead built specialized gravitational wave detectors that can detect and characterize the ripples in spacetime produced by masses spiraling into, merging with, and ringing down from interactions with one another.
On September 14, 2015, our knowledge of the world forever changed with the first direct detection of gravitational waves from merging black holes. Since that event, some ~60 additional gravitational wave signals have been seen, including not only merging black holes, but merging neutron stars as well. The past five years have validated Einstein as never before, proving many of General Relativity’s predictions right. Over the next few years, gravitational waves will have an unprecedented opportunity to put our theory of gravity to the test as never before. Although you should never bet against Einstein, new ways of probing the Universe always have an opportunity to show us that it doesn’t behave how we might have expected. Here’s how gravitational waves might wind up proving Einstein wrong.
According to General Relativity, gravitational waves arise as an entirely new type of radiation, separate from anything known before. Whenever a mass accelerates through a region of curved space, or whenever a constantly moving mass moves through a region of space where the curvature is changing, the changes to the curvature of space generate ripples, similar to water ripples whenever a raindrop falls into a pond. These ripples, however: don’t require a medium to travel through; simply the fabric of space is enough, carry energy away from whatever system generated them, and travel exactly at the speed of light.
Up until 2015, this was all theory, with only indirect tests available to confirm small aspects of this. But the advances made in laser interferometry, as originally leveraged by the LIGO collaboration and later joined by Virgo, enabled us to detect the ripples in space as gravitational waves passed through the Earth. These waves, indeed, passed through Earth at the speed of light, alternately stretching-and-compressing space in perpendicular directions, enabling us to “see” these gravitational waves for the first time.
As the waves passed through the Earth, the stretching in one direction caused light to require a little bit more time to traverse it, while the compressing in the perpendicular direction reduced the light-travel-time by an equivalent amount. With slight changes in the length of each laser arm in the presence of a gravitational wave, the interference pattern that the light traveling in these interferometer arms creates gets altered by a tiny bit. By observing the patterns that change in multiple detectors, we can reconstruct properties of not only the sources that created these waves, but the waves themselves.
In addition, a now-famous 2017 event revealed the merger of two neutron stars, where gravitational waves arrived in a burst, and then just 1.7 seconds after that burst ended, the first light signal arrived. Finally, we could measure the speed of gravity to unprecedented precision, and found that it equaled the speed of light to 1 part in ~1015. The speed, frequency, amplitude, and energy of these gravitational waves, to the best of our measurement abilities, agreed perfectly with what Einstein predicted.
But each time we measure something new — to greater precision, for longer durations, at increased sensitivities, in a new frequency range, for a novel class of objects, etc. — there’s a chance that what we see will take us beyond known physics. While Einstein’s General Theory of Relativity is purely a tensor theory, where the presence of matter and energy alone tells space how to curve, and the curvature of space alone tells matter and energy how to move, there are other possibilities.
There could be either a scalar and/or a vector component to gravity as well, which many attempted extensions to or modified theories of gravity introduce. While General Relativity predicts that the speed of gravity must always equal exactly the speed of light, many of these alternative theories of gravity incorporate an intriguing set of possibilities for something different. As it turns out, detailed observations of black hole-black hole mergers, to even greater sensitivities than we’re capable of measuring right now, might be exactly what finally takes us beyond Einstein.
To understand how this could work, let’s start by thinking about something far more familiar: light. When we observe light from any source in the Universe, we see that it comes in a variety of energies, which correspond to a variety of wavelengths and frequencies. However, light, if it travels through a vacuum, is always an electromagnetic wave, meaning it generates alternating electric and magnetic fields as it speeds through the Universe. Additionally, light of all wavelengths and energies, so long as it travels through the vacuum of space, always moves at exactly the same speed: the speed of light.
If you were to take all of the light in the Universe from a particular source and measure each individual quantum of energy, you’d find that the light could actually be decomposed into a combination of two different polarizations: clockwise and counterclockwise. In the vacuum of space, without any matter or other sources of energy to interfere with it, all forms of light travel at exactly the same speed, regardless of energy, wavelength, intensity, or polarization...
[To continue, read the article from the link above]
Over the past five years, humanity has begun to practice a wholly new type of astronomy: gravitational wave astronomy. Instead of looking at some form of light coming from the Universe — gathered with a telescope, radio dish, antenna, or some other equipment sensitive to electromagnetic radiation — we’ve instead built specialized gravitational wave detectors that can detect and characterize the ripples in spacetime produced by masses spiraling into, merging with, and ringing down from interactions with one another.
On September 14, 2015, our knowledge of the world forever changed with the first direct detection of gravitational waves from merging black holes. Since that event, some ~60 additional gravitational wave signals have been seen, including not only merging black holes, but merging neutron stars as well. The past five years have validated Einstein as never before, proving many of General Relativity’s predictions right. Over the next few years, gravitational waves will have an unprecedented opportunity to put our theory of gravity to the test as never before. Although you should never bet against Einstein, new ways of probing the Universe always have an opportunity to show us that it doesn’t behave how we might have expected. Here’s how gravitational waves might wind up proving Einstein wrong.
According to General Relativity, gravitational waves arise as an entirely new type of radiation, separate from anything known before. Whenever a mass accelerates through a region of curved space, or whenever a constantly moving mass moves through a region of space where the curvature is changing, the changes to the curvature of space generate ripples, similar to water ripples whenever a raindrop falls into a pond. These ripples, however: don’t require a medium to travel through; simply the fabric of space is enough, carry energy away from whatever system generated them, and travel exactly at the speed of light.
Up until 2015, this was all theory, with only indirect tests available to confirm small aspects of this. But the advances made in laser interferometry, as originally leveraged by the LIGO collaboration and later joined by Virgo, enabled us to detect the ripples in space as gravitational waves passed through the Earth. These waves, indeed, passed through Earth at the speed of light, alternately stretching-and-compressing space in perpendicular directions, enabling us to “see” these gravitational waves for the first time.
As the waves passed through the Earth, the stretching in one direction caused light to require a little bit more time to traverse it, while the compressing in the perpendicular direction reduced the light-travel-time by an equivalent amount. With slight changes in the length of each laser arm in the presence of a gravitational wave, the interference pattern that the light traveling in these interferometer arms creates gets altered by a tiny bit. By observing the patterns that change in multiple detectors, we can reconstruct properties of not only the sources that created these waves, but the waves themselves.
In addition, a now-famous 2017 event revealed the merger of two neutron stars, where gravitational waves arrived in a burst, and then just 1.7 seconds after that burst ended, the first light signal arrived. Finally, we could measure the speed of gravity to unprecedented precision, and found that it equaled the speed of light to 1 part in ~1015. The speed, frequency, amplitude, and energy of these gravitational waves, to the best of our measurement abilities, agreed perfectly with what Einstein predicted.
But each time we measure something new — to greater precision, for longer durations, at increased sensitivities, in a new frequency range, for a novel class of objects, etc. — there’s a chance that what we see will take us beyond known physics. While Einstein’s General Theory of Relativity is purely a tensor theory, where the presence of matter and energy alone tells space how to curve, and the curvature of space alone tells matter and energy how to move, there are other possibilities.
There could be either a scalar and/or a vector component to gravity as well, which many attempted extensions to or modified theories of gravity introduce. While General Relativity predicts that the speed of gravity must always equal exactly the speed of light, many of these alternative theories of gravity incorporate an intriguing set of possibilities for something different. As it turns out, detailed observations of black hole-black hole mergers, to even greater sensitivities than we’re capable of measuring right now, might be exactly what finally takes us beyond Einstein.
To understand how this could work, let’s start by thinking about something far more familiar: light. When we observe light from any source in the Universe, we see that it comes in a variety of energies, which correspond to a variety of wavelengths and frequencies. However, light, if it travels through a vacuum, is always an electromagnetic wave, meaning it generates alternating electric and magnetic fields as it speeds through the Universe. Additionally, light of all wavelengths and energies, so long as it travels through the vacuum of space, always moves at exactly the same speed: the speed of light.
If you were to take all of the light in the Universe from a particular source and measure each individual quantum of energy, you’d find that the light could actually be decomposed into a combination of two different polarizations: clockwise and counterclockwise. In the vacuum of space, without any matter or other sources of energy to interfere with it, all forms of light travel at exactly the same speed, regardless of energy, wavelength, intensity, or polarization...
[To continue, read the article from the link above]
