- 3479 - EINSTEIN - untangling his weird theories? The past 100 years have witnessed spectacular upheavals to our understanding of space and time. The next 10 years holds the promise of taking these insights to an entirely new level.
--------------------- 3479 - EINSTEIN - untangling his weird theories?
- Everyday experience affirms that if you and I measure the lengths of objects or the durations of events, our results will agree. But in June, 1905, Albert Einstein realized that everyday experience is deeply misleading. During the course of five intense weeks that he described as having a storm break out in his mind, Einstein established that if you and I are moving relative to one another, our watches will tick off time at different rates and our tape measures will have different lengths. At familiar speeds, the effects are tiny, explaining why, for so long, no one had noticed.
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- Einstein’s mathematical derivation of the conclusion was so simple, relying on nothing more advanced than high-school algebra, that the community of physicists quickly relinquished common intuition in favor of a startlingly new flexibility of space and time.
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- There is now no controversy that were you to take a round-trip journey at nearly light speed, upon landing back on Earth, you would find that you had traveled far into the future?????
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- In 1915, Einstein went further still, realizing that distortions to space and time could be yet more severe: Massive objects cause the fabric of spacetime to sag, somewhat like a bowling ball resting on a trampoline. Such spacetime curvature then affects the motion of nearby objects, such as a planet moving near a star, leading to a new and demonstrably deeper understanding of gravitational force:
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------ Gravity is nothing but grooves in the spacetime fabric that guide an object’s motion.
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- These results constitute Einstein’s special and general theories of relativity, and have led to profound insights into the origin of the universe, the nature of blackholes and, most recently, gravitational waves, which are ripples in the very fabric of spacetime.
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- Einstein’s relativity does not say what space and time actually are. When we speak of the spacetime fabric, that is a metaphor? Are space and time material things? And if so, can we identify the threads stitching the spacetime fabric?
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- Einstein was awarded the 1921 Nobel Prize, but not for his discoveries in relativity. The Nobel committee cited Einstein’s work on the “photoelectric effect“, which was one of the earliest and most influential papers on what would become quantum mechanics, the curious laws that are most manifest in the microworld of atoms and particles.
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- In 1935, working with two colleagues, Einstein believed that he had finally pinpointed quantum mechanics’ Achilles heel. Relying on a feature of the theory known as “quantum entanglement“, Einstein argued that two distinct and widely separated particles could act as though they are single entity.
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- One member of the pair might be in New York and the other might be in Calgary. Yet, were you to interact with one of the particles, quantum mechanics predicts that you would instantaneously influence measurable properties of the other, even though it is thousands of kilometers away.
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- Einstein considered this implication of quantum theory to be ludicrous, famously deriding it with the characterization “spooky.” He envisioned that his colleagues would have to agree that quantum mechanics was, at best, a “provisional description” of the world, but not real.
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- Decades after Einstein died, experiments established that spooky connections are real.
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- Physicists have realized that “quantum entanglement” is relevant not only to particles within space but to space itself. Space is permeated by fields, electric, magnetic, nuclear, gravitational, and , depending on their overall configuration, quantum mechanics establishes relationships between the properties of the fields at different locations.
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- When the fields have the least amount of energy possible, the emptiest that empty space can be, these relationships amount to “quantum mechanics entangling” different locations throughout empty space.
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- Brilliant scientists at the forefront of research have leveraged the mathematics underlying such connections to argue that the fabric of space may in fact be stitched by the threads of quantum entanglement. Cut the invisible quantum threads and the fabric of space would unravel.
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- For hundreds of years, physicists took space and time as givens, bedrock ingredients in the makeup of reality. In the coming years, quantum mechanics may help us understand the weave of the spacetime fabric, perhaps explaining why they exist at all.
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- Another effect predicted by Albert Einstein has been identified in a double star system about 29,000 light years from Earth. This phenomenon, called a 'gravitational redshift,' has been well documented in our Solar System, but it's been more elusive farther away.
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- Scientists saw evidence for this effect in the X-rays from a system with a neutron star in close orbit with a companion star. What do Albert Einstein, the Global Positioning System (GPS), and a pair of stars 200,000 trillion miles from Earth have in common?
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- The answer is an effect from Einstein's General Theory of Relativity called the "gravitational redshift," where light is shifted to redder colors because of gravity. Using NASA's Chandra X-ray Observatory, astronomers have discovered the phenomenon in two stars orbiting each other in our galaxy about 29,000 light years (200,000 trillion miles) away from Earth.
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- While these stars are very distant, gravitational redshifts have tangible impacts on modern life, as scientists and engineers must take them into account to enable accurate positions for GPS.
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- While scientists have found incontrovertible evidence of gravitational redshifts in our solar system, it has been challenging to observe them in more distant objects across space. The new Chandra results provide convincing evidence for gravitational redshift effects at play in a new cosmic setting.
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- The system known as “4U 1916-053” contains two stars in a remarkably close orbit. One is the core of a star that has had its outer layers stripped away, leaving a star that is much denser than the Sun. The other is a neutron star, an even denser object created when a massive star collapses in a supernova explosion.
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- These two compact stars are only about 215,000 miles apart, roughly the distance between the Earth and the Moon. While the Moon orbits our planet once a month, the dense companion star in “4U 1916-053” whips around the neutron star and completes a full orbit in only 50 minutes.
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- The team analyzed X-ray spectra, the amounts of X-rays at different wavelengths, from Chandra. They found the characteristic signature of the absorption of X-ray light by iron and silicon in the spectra. In three separate observations with Chandra, the data show a sharp drop in the detected amount of X-rays close to the wavelengths where the iron or silicon atoms are expected to absorb the X-rays.
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- The wavelengths of these characteristic signatures of iron and silicon were shifted to longer, or redder wavelengths compared to the laboratory values found here on Earth. The researchers found that the shift of the absorption features was the same in each of the three Chandra observations, and that it was too large to be explained by motion away from us. Instead they concluded it was caused by gravitational redshift.
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- How does this connect with General Relativity and GPS? As predicted by Einstein's theory, clocks under the force of gravity run at a slower rate than clocks viewed from a distant region experiencing weaker gravity.
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- This means that clocks on Earth observed from orbiting satellites run at a slower rate. To have the high precision needed for GPS, this effect needs to be taken into account or there will be small differences in time that would add up quickly, calculating inaccurate positions.
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- All types of light, including X-rays, are also affected by gravity. An analogy is that of a person running up an escalator that is going down. As they do this, the person loses more energy than if the escalator was stationary or going up. The force of gravity has a similar effect on light, where a loss in energy gives a lower frequency. Because light in a vacuum always travels at the same speed, the loss of energy and lower frequency means that the light, including the signatures of iron and silicon, shift to longer wavelengths.
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- This is the first strong evidence for absorption signatures being shifted to longer wavelengths by gravity in a pair of stars that has either a neutron star or blackhole.
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- Strong evidence for gravitational redshifts in absorption has previously been observed from the surface of white dwarfs, with wavelength shifts typically only about 15% of that for 4U 1916-053.
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- It is likely that a gaseous atmosphere blanketing the disk near the neutron star absorbed the X-rays, producing these results. The size of the shift in the spectra allowed the team to calculate how far this atmosphere is away from the neutron star, using General Relativity and assuming a standard mass for the neutron star.
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- They found that the atmosphere is located 1,500 miles from the neutron star, about half the distance from Los Angeles to New York and equivalent to only 0.7% of the distance from the neutron star to the companion. It likely extends over several hundred miles from the neutron star.
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- In two of the three spectra there is also evidence for absorption signatures that have been shifted to even redder wavelengths, corresponding to a distance of only 0.04% of the distance from the neutron star to the companion.
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- Relativity continues to test the limits of physics more than any other discovery Einstein made. Relativity is based on one powerful idea:
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------------------- Every observer in the universe sees the same laws of nature in operation.
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- For example, a friend drives by and throws a ball in the air and then catches it when it falls. Your friend sees the ball go up and down while you see it travel in an arc, but you both agree that Newton’s laws of motion govern the ball’s path. It’s a different description of events but with the same laws operating.
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- Special relativity says the laws of nature are the same in all frames of reference moving at a constant velocity. General relativity says the laws are the same in all frames.
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- If your friend’s car is moving at a steady speed, the laws of special relativity apply, but if the car is accelerating, we have to apply general relativity. Most of the weird results we know about relativity — the fact that moving clocks slow down, moving objects shrink in the direction of motion and get more massive, and even the best known scientific equation, E = mc^2 — follow from the principle of special relativity.
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- NASA used its Gravity Probes A and B to confirm how a clock ticks slower in orbit than on Earth and that our planet’s gravitation drags space-time with it. Light takes longer to pass between two points when one is near a massive object. Astronomers confirmed this by bouncing light off Mercury when it was near the Sun and away from it.
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- After 100 years, physicists are still trying to understand the far-reaching implications of Relativity. Scientists are in the middle of a sweeping search for the “gravitational waves” Einstein predicted in 1916 as a result of his general theory of relativity.
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- Theorists haven’t yet tied Einstein’s successful predictions about the large-scale universe to quantum mechanics, the best theory of physics at subatomic scales.
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- Stretch a light wave out, and you have a microwave. Scrunch it up, and you have an X-ray. All of these waves move at the same speed, what we call the “speed of light” and denote by the letter “c“.
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- If the principle of relativity is really true, and if all the laws of nature (including Maxwell’s equations) are really the same in all frames of reference, then the speed of light has to be the same for all observers.
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- This is really a weird statement. It says, for example, if a friend is driving by you in a car at 60 mph and shines a flashlight, both of you will see that light traveling at 186,000 miles per second. To emphasize the strangeness, this means that standing on the ground, you will not see that light moving at 186,000 miles per second plus 60 mph, as you might expect, but at 186,000 miles per second.
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- Einstein was the first to realize that the only way to resolve this dilemma was to change the way we think about space (i.e., distance) and time. We arrived at the dilemma by thinking about velocities, and velocity is just distance divided by time. Change our ideas about space and time, Einstein argued, and these sorts of problems could go away.
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- Relativity tells us that the same laws of nature hold true everywhere in the universe. This “equivalence principle” also confirms that two bodies fall through a gravitational field at the same rate regardless of their mass.
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------------------------------ General relativity is still our best theory of gravitation.
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- Imagine a ship traveling in deep space. If the ship is moving at a constant velocity and a passenger holds a ball out and lets it go, the ball will simply stay where it was released. If, however, the ship is accelerating, the situation will be different. The ball will continue to move with the velocity it had when it was released, but the ship will be speeding up. From outside the spaceship, we would say that the floor came up and hit the ball. To the passenger, however, it would appear that the ball fell.
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- If the ship were accelerating at 32 feet per second squared , the ball would appear to fall in the same way it would on Earth’s surface. Thus, once acceleration enters the picture and general relativity takes over, we can describe the effects of gravity in a new way.
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- To talk about the universe in the first fraction of a second after the Big Bang, back when matter was packed together in unimaginable densities, and blackholes couldn’t be described at all.
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- The presence of matter distorts the fabric of space and time, and objects travel on the shortest path in that distorted space-time.
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March 1, 2022 EINSTEIN - untangling his weird theories? 3479
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