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------------ 2749 - GRAVITY - does it travel at the speed of light?
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- One hundred years ago today, on May 29, 1919, measurements of a solar eclipse offered verification for Einstein's theory of general relativity. Even before that, Einstein had developed the theory of special relativity, which revolutionized the way we understand light. Light is a particle / wave that we call a “photon.
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- Studying cosmic rays which are hydrogen atom nuclei and superfast, or relativistic, “particles” can help protect missions exploring the solar system, traveling to the Moon, and they can teach us more about our galactic neighborhood. A well-aimed near-light-speed particle can trip onboard electronics and too many at once could have negative radiation effects on space-faring astronauts as they travel to the Moon, or beyond.
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- There are three ways that this particle acceleration happens. One is with “electromagnetic fields’. Most of the processes that accelerate particles to relativistic speeds work with electromagnetic fields. The two components, electric and magnetic fields, like two sides of the same coin, work together to accelerate particles at relativistic speeds throughout the universe.
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- Electric and magnetic fields can add and remove energy from particles, changing their speeds. Electromagnetic fields accelerate charged particles because the particles feel a force in an electromagnetic field that pushes them along, similar to how gravity pulls at objects with mass. In the right conditions, electromagnetic fields can accelerate particles at near-light-speed.
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- On Earth, electric fields are often specifically harnessed on smaller scales to speed up particles in laboratories. Particle accelerators, like the Large Hadron Collider and Fermilab, use pulsed electromagnetic fields to accelerate charged particles up to 99.99999896% the speed of light.
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- At light speeds, the particles can be smashed together to produce collisions with immense amounts of energy. This allows scientists to look for elementary particles and understand what the universe was like in the very first fractions of a second after the Big Bang.
- Another way particles are accelerated is with “magnetic explosions”. Magnetic fields are everywhere in space, encircling Earth and spanning the solar system. They even guide charged particles moving through space, which spiral around the fields.
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- When these magnetic fields run into each other, they can become tangled. When the tension between the tangled crossed lines becomes too great, the lines explosively snap and realign in a process known as magnetic reconnection.
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- The rapid change in a region's magnetic field creates electric fields, which causes all the attendant charged particles to be flung away at high speeds. Scientists suspect magnetic reconnection is one way that particles, for example, the solar wind, which is the constant stream of charged particles from the sun, is accelerated to relativistic speeds.
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- Those speedy particles also create a variety of side-effects near planets. Magnetic reconnection occurs close to us at points where the sun's magnetic field pushes against Earth's magnetosphere, the Earth’s protective magnetic environment.
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- When magnetic reconnection occurs on the side of Earth facing away from the sun, the particles can be hurled into Earth's upper atmosphere where they spark the auroras.
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- Magnetic reconnection is also thought to be responsible around other planets like Jupiter and Saturn, though in slightly different ways.
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- NASA's spacecraft have been designed and built to focus on understanding all aspects of magnetic reconnection. Using four identical spacecraft, the mission flies around Earth to catch magnetic reconnection in action. The results of the analyzed data can help scientists understand particle acceleration at relativistic speeds around Earth and across the universe.
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- A third way particles are accelerated is with Wave-Particle Interactions. When electromagnetic waves collide, their fields can become compressed. Charged particles bouncing back and forth between the waves can gain energy similar to a ball bouncing between two merging walls.
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- These types of interactions are constantly occurring in near-Earth space and are responsible for accelerating particles to speeds that can damage electronics on spacecraft and satellites in space. NASA missions, like the Van Allen Probes, help scientists understand wave-particle interactions.
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- Wave-particle interactions are also thought to be responsible for accelerating some cosmic rays that originate outside our solar system. After a supernova explosion, a hot, dense shell of compressed gas called a blast wave is ejected away from the stellar core.
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- Filled with magnetic fields and charged particles, wave-particle interactions in these bubbles can launch high-energy cosmic rays at 99.6% the speed of light. Wave-particle interactions may also be partially responsible for accelerating the solar wind and cosmic rays from the sun.
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- Gravity itself travels at the speed of light? Astronomers have measured this when
two neutron stars collided and the resulting gravitational wave spread at the speed of light. The neutron stars which are dead cores of two stars collided 130 million years ago in a galaxy somewhat far away.
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- The collision was so extreme that it caused a wrinkle in space-time, called a gravitational wave. That gravitational wave and the light from the stellar explosion traveled together across the cosmos. They arrived at Earth simultaneously at 6:41 a.m. Eastern on August 17, 2019.
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- The event prompted worldwide headlines. Astronomers had waited a generation for this moment. But it was also the first-ever direct confirmation that gravity travels at the speed of light.
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- We all know light obeys this speed limit, roughly 186,000 miles per second. Nothing travels faster. But why should gravity travel at the same speed? That question requires an understanding of Albert Einstein’s general relativity, the theory of gravity, which is the same theory that predicted gravitational waves a century ago.
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- Einstein overthrew Isaac Newton’s idea of “absolute time.” Newton thought time marched onward everywhere at an identical pace, regardless of how we mortals perceived it. It was unflinching. By that line of thinking, one second on Earth is one second near a black hole, which he didn’t know existed.
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- Newton also thought gravity acted instantaneously. Distance didn’t matter. But then Einstein showed that time is “relative“. It changes with speed and in the presence of gravity. One of the ramifications of that is that you can’t have simultaneous actions at a distance. So information of any kind has a finite speed, whether it’s a photon, the light-carrying particle, or a graviton, which carries the force of gravity.
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- “In relativity, there is a ‘speed of information’, the maximum speed that you can send information from one point to another”.
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- In electromagnetism, when you shake an electron, it creates a change in the electric field that spreads out at the speed of light. Gravity works the same way. Shake a mass and the change in the gravitational field, the gravitational wave, propagates at that same speed.
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- So the fact that the speed of gravitational waves is equal to the speed of electromagnetic waves is simply because they both travel at the speed of information.
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- There’s an easy way to picture this, too. Imagine the sun vanished right now. Earth wouldn’t just drift into space instantly. After eight minutes, Earth would go dark and simultaneously push off in a straight line.
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- Let’s hope this doesn’t happen.
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---------------------------------------- More reviews on the subject:
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- 2656 - GRAVITY - in supernovae explosions. Is the force of gravity instantaneous across the Universe? Or does gravity have a speed limit to how fast the force can travel.? This is not as simple a question as it seems on the surface.
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- 2628 - GRAVITY WAVES - from supernovae explosions? Is the speed of gravity instantaneous, or is there a speed limit on how fast the force of gravity can travel. This is not as simple a question. After all, we know how fast light travels, and if the Sun were to suddenly wink out of existence, we’d still receive light from it for just over 8 minutes after it disappeared!
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- 2438 - GRAVITY - traveling at the speed of light? If the Sun went dark instantaneously we would not know it until 8 minutes later., when the last bit of light reached us. The same delay would occur with gravity. If the Sun disappeared altogether the Earth would continue to orbit for another 8 minutes before it would shoot off into space in a straight line.
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- 2356 - If a gravity wave comes through the detector it would sound like a “chirp”. This chirp could be a very old gravity wave. Today the Universe is 13.7 billion years old. Light, or photon, did not appear until 100,000 years after the Big Bang. But gravity started at the first instant, 10^-43 seconds after the beginning. Studying gravity waves will allow us to peer far back in to the beginning of time and space.
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- 2176 - The Gravity of the Details. Maybe it is time for someone to discover some new physics for gravity. Those gnawing details need to be reconciled. Facts are messing with our theories. Dark Matter and Pioneer anomalies could disappear with new equations.
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- 2175 - Why is gravity so small?. You would not have come up with this question
naturally because we thing of gravity is being big. A big powerful force. Just try to lift 100 pounds. But, you have to realize the other part of gravity is the mass of the Earth and it is very, very big, 13,200,000,000,000,000,000,000,000 pounds. Yet, a small magnet will pick up a paper clip that the entire Earth can not hold on to.
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- 2174 - Gravity - What is it Really? - Gravity is the force that causes masses to attract each other. Or, maybe, gravity is not a force. Maybe gravity is the least energy way for mass to travel through spacetime. Mass tells spacetime how to bend. Spacetime tells mass how to move. These two different explanations appear to be totally unrelated in explaining the same thing, gravity.
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- 2170 - Gravitational waves are the next way to measure the expansion rate of the universe. The two other methods being used to measure expansion are Supernovae Type1a and Acoustic waves in the cosmic microwave background. Their answers differ by 9%. This is not even close enough for government work, let alone astronomy.
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- 2127 - Einstein's Ring. How can empty space bend light? How can time slow down or speed up? Is it not the same everywhere in the universe? If general relativity holds true on the scale of entire galaxies then 95% of the universe is made up of invisible substances called dark matter and dark energy.
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- 2089 - In 1687 when Sir Isaac Newton was 45 years old he detailed the laws of gravity in a simple equation. F = G * M1*M2 /r^2. In 1850 Jean Joseph LeVenier noticed that when using Newton’s equations for gravity to calculate the orbit of Mercury results were a little off. 230 years after Newton’s equations, Albert Einstein, in 1916, came up with a more detailed equation for gravity that included the bending of space and time in the presence of mass. Science is just not satisfied for this accuracy in their equations. Either the equations are off making the math off, or, the astronomers' measurements are in error.
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- May 29, 2020 2749
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