- 3323 - - UNIVERSE - spooky action at distance? The Friedmann equations which relates the universe’s expansion rate to the sum total of all the different forms of matter and energy within it has been known for 99 years and applied to the universe for almost as long.
--------------------- 3323 - UNIVERSE - spooky action at distance?
- Newton’s theory of gravity stated that gravity acted at a distance and “instantaneously“. Einstein showed that not to be the case. His general theory of relativity exorcised Newton’s mysterious action-at-a-distance by having gravity traveling at the speed of light and acting locally in a “curved space“.
- To Einstein’s horror, quantum physics boasts a very “spooky action at a distance,” In November 1915, Albert Einstein presented his general theory of relativity to a bewildered Prussian Academy of Sciences in Berlin, the theory that revolutionized our view of the universe.
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- Isaac Newton in 1686 had a theory for gravity that worked beautifully describing a host of gravitational phenomena, from the orbits of planets and comets around the sun to the tides and the oblateness of the Earth. The Earth is an oblate spheroid, slightly flattened at the poles.
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- Rocket engineers still use Newton’s theory to calculate their paths to reach other moons and planets in the solar system. The theory only begins to fail when gravitational forces are extremely strong, far from our everyday lives.
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- At the very core of Newton’s theory is the notion of “action at a distance,” the assumption that any two massive objects will attract each other gravitationally instantaneously and without any direct action on one another. Not so!
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- According to Einstein’s special theory of relativity from 1905, nothing could travel faster than the speed of light, not even gravity. A disturbance in the gravitational force would have to propagate at most at the speed of light and never be instantaneous.
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- By attaching gravitational attraction to the curvature of space, Einstein also got rid of the mysterious “action at a distance“. Space was stretchy, and gravity was a response to moving in this stretchy space.
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- The return of “spooky action at a distance” occurred when quantum mechanics was on the rise. Among its many weird behaviors, the notion of “quantum superposition” really defies our imagination.
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- In our everyday life, you are in one place. Not so for quantum systems. An electron, for example, is not a thing in one place but a thing in many places at once. This “spatial superposition” theory is absolutely essential to describe quantum systems.
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- The equations even describe this superposition of positions as the probability of finding the electron here or there once its position is measured. The probability is the square of the amplitudes of these quantum waves. So, quantum mechanics is about the potentiality of something to be found here or there, not about where something is all the time. Until there is a measurement, the notion of where something is does not make sense!
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- This indeterminacy drove Einstein nuts. It was precisely the opposite of what he had found with his theory of gravity. Gravity acted locally in determining the curvature of space at every point, and also always at the speed of light. Einstein believed that nature should be reasonable, amenable to rational explanation, and predictable. “Quantum mechanics had to be wrong or at least incomplete“.
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- In 1935, two decades after Einstein’s paper on general relativity, he wrote a paper with Boris Podolsky and Nathan Rosen trying to expose the craziness of quantum mechanics, calling it “spooky action at a distance.”
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- When one looks at quantum systems with two particles, say two electrons in a superposition, so that now the equations describe both of them together, they are in an entangled state that seems to defy all that Einstein believed in.
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- If you measure the property of one electron, say its rotation, you can tell what the other electron’s rotation is, without even bothering to measure it. Even weirder, this ability to tell one from the other persists for arbitrarily large distances and appears to be instantaneous. In other words, quantum spookiness defies both space and time.
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- Experiments have confirmed that entanglement can persist for astronomically large distances. It is as if an entangled state exists in a realm where spatial distances and time intervals simply don’t matter.
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- It is true that such entangled states are very fragile and can easily be destroyed by different kinds of interference. They do teach us that there are many mysterious aspects to nature that remain beyond our comprehension. Einstein is right quantum mechanics is spooky.
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- Einstein's General Relativity relates the curvature of space to what is present inside of it, but the equation has infinite variations. One very general class of spacetimes obeys the same straightforward equation, “the Friedmann equation“. Just by measuring the universe today, we can extrapolate all the way back to the Big Bang, 13.8 billion years in our past.
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- Newtonian physics works just fine until you go down to very small distances (where quantum mechanics comes into play), get close to a very large mass (when general relativity becomes important), or start moving close to the speed of light (when special relativity matters).
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- The universe, as we know it today, is expanding, cooling, and getting clumpier and less dense as it ages. On the largest cosmic scales, things appear to be uniform; if you were to place a box a few billion light-years on a side anywhere within the visible universe, you’d find the same average density, everywhere, to 99.997% precision.
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- Space, instead of being an unchanging backdrop for masses to exist and move in, became inextricably tied to time, as the two were woven together in a fabric: spacetime. Nothing could move through spacetime faster than the speed of light, and the more rapidly you moved through space, the slower you moved through time (and vice versa).
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- Whenever and wherever not just mass but any form of energy was present, the fabric of spacetime curved, with the amount of curvature being directly related to the stress-energy content of the universe at that location. Spacetime’s curvature told matter and energy how to move through it, while the presence and distribution of matter and energy told spacetime how to curve.
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- In the Friedmann equation the left-hand-side is the expansion rate of the universe (squared), while the right hand side represents all the forms of matter and energy in the universe, including spatial curvature and a cosmological constant.
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- In 1916, when Karl Schwarzschild discovered the solution for a nonrotating point mass, which we identify today with a blackhole. If you decide to put down a second mass in your universe, your equations are now unsolvable.
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- If, the universe were filled uniformly with some sort(s) of energy, matter, radiation, a cosmological constant, or any other form of energy you can imagine, and, that the energy is distributed evenly in all directions and in all locations, then his equations provided an exact solution for spacetime’s evolution.
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- What Friedmann found was that this solution was inherently unstable over time. If your universe began from a stationary state and was filled with this energy, it would inevitably contract until it collapsed from a singularity. The other alternative is that the universe expands, with the gravitational effects of all the different forms of energy working to oppose the expansion.
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- While matter and radiation become less dense as the universe expands owing to its increasing volume, “dark energy” is a form of energy inherent to space itself. As new space gets created in the expanding universe, the dark energy density remains constant.
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- The first Friedmann equation was a mathematical idea that of a differential equation. A differential equation, in physics, is an equation where you begin at some initial state, with properties that you choose to best represent the system you have.
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- Have the particles positions, momentum, masses, and other properties of interestand apply the differential equation. It tells you how, based on the conditions your system began with, it will evolve to the very next instant. Then, from the new positions, momenta, and all the other properties that you could derive, you can put them back into the very same differential equation and it will tell you how the system will evolve to the very next moment.
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- From Newton’s laws to the time-dependent Schrödinger equation, differential equations tell us how to evolve any physical system either forward or backward in time.
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- But there’s a limitation here: You can only keep this game up for so long. Once your equation no longer describes your system, you’re extrapolating beyond the range over which your approximations are valid.
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- For the first Friedmann equation, you need the contents of your universe to remain constant. Matter remains matter, radiation remains radiation, a cosmological constant remains a cosmological constant, and there are no transformations allowed from one species of energy to another.
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- You also need your universe to remain isotropic and homogeneous. If the universe gains a preferred direction or becomes too nonuniform, these equations no longer apply. .
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- Do galaxies rotate clockwise more frequently than they rotate counterclockwise? Is there evidence that quasars only exist at multiples of a specific redshift? Does the cosmic microwave background radiation deviate from a blackbody spectrum? Are there structures that are too large to explain in a universe that is, on average, uniform?
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- The only frame of reference that’s notable is the one where the Big Bang’s leftover glow appears uniform in temperature. Galaxies are just as likely to be “left-handed” as “right-handed.” Quasar redshifts are definitively not quantized.
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- Today our universe consists of about 68% dark energy, 27% dark matter, about 4.9% normal matter, about 0.1% neutrinos, about 0.01% radiation, and negligible amounts of everything else. When we extrapolate that both backward and forward in time, we can learn how the universe expanded in the past and will expand in the future.
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- The relative importance of different energy components in the universe at various times in the past when dark energy reaches a number near 100% in the future, the energy density of the universe (and, therefore, the expansion rate) will asymptote to a constant, but will continue to drop so long as matter remains in the universe.
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- Stars exist, and when they burn through their fuel, they convert some of their rest-mass energy (normal matter) into radiation, changing the composition of the universe.
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- Gravitation occurs, and the formation of structure creates an inhomogeneous universe with large differences in density from one region to another, particularly where blackholes are present.
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- Neutrinos first behave as radiation when the universe is hot and young, but then behave as matter once the universe has expanded and cooled.
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- Very early in the history of the universe, the cosmos was filled with the equivalent of a cosmological constant, which must have decayed away (signifying the end of inflation) into the matter and energy that populates the universe today.
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- The quantum fluctuations that occur during inflation get stretched across the universe, and when inflation ends, they become “density fluctuations“. This leads, over time, to the large-scale structure in the universe today, as well as the fluctuations in temperature observed in the Cosmic Microwave Background.
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- The effects of gravitation have been well studied and quantified , and while it can slightly affect the expansion rate on local cosmic scales, the global contribution doesn’t impact the overall expansion.
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- We can account for neutrinos precisely to the limit of how well known their rest masses are, so there’s no confusion there. The only issue is that, if we go back early enough, there’s an abrupt transition in the energy density of the universe, and those abrupt changes, as opposed to smooth and continuous ones, are the ones that can truly invalidate our use of the first Friedmann equation.
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- After enough time goes by, the acceleration will leave every bound galactic or supergalactic structure completely isolated in the universe, as all the other structures accelerate irrevocably away.
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- We can only look to the past to infer dark energy’s presence and properties, which require at least one constant, but its implications are larger for the future.
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- The Friedmann equations which relates the universe’s expansion rate to the sum total of all the different forms of matter and energy within it has been known for 99 years and applied to the universe for almost as long.
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- This equation has shown us how the universe has expanded over its history, and it enables us to predict what our ultimate fate will be, even in the ultra-distant future. But can we be certain our conclusions are correct?
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- Only to a particular level of confidence. Beyond the limitations of our data, we must always remain skeptical of drawing even the most compelling conclusions. Beyond the known, our best predictions remain speculations.
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- October 31, 2021 UNIVERSE - spooky action at distance? 3323
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