- 2911 - PHYSICS - unsolved mysteries? 1900, the British physicist Lord Kelvin is said to have pronounced: "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.” There are many mysteries we need to learn before we get hit by the next asteroid. Our Universe is full of surprises:
STARS CIRCLING THE BLACK HOLE AT GALAXY CENTER.
--------------------------- 2911 - PHYSICS - unsolved mysteries
- A low-flying space rock set a record last Friday, November 13, 2020. On Friday the 13th “VT4 asteroid”, passed just under 250 miles above the Southern Pacific.
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- The asteroid was spotted by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey at the Mauna Loa Observatory in Hawaii in the early morning hours of Saturday, November 14th, just 15 hours after approach.
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- This is not uncommon for fast-movers, especially asteroids that are coming at the Earth from our sunward blind-spot, like 2020 VT4.
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- The asteroid- 2020 VT4 is estimated to be 5-10 meters (16-32 feet) across, about the size of a small house. Earth juust missed occupying the same space as the perihelion point for the asteroid, which occurred just 20 hours prior to Earth passage.
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- This sets a record for the closest documented non-meteoric asteroid pass versus the Earth. This record was already broken once this year, with the passage of asteroid 2020 QG 1,864 miles from the surface of the Earth on August 16th.
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- A brilliant “bolide” was captured on video on the afternoon of August 10th, 1972, as it became a brilliant daytime fireball over the Grand Teton Mountains in Wyoming before skipping back out of the Earth’s atmosphere.
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- Another recent record was set in October 2008, when astronomers spotted 4-meter (13 foot) asteroid 2008 TC3 19 hours prior to impact,and later recovered fragments in the Nubian Desert in northern Sudan two months later, making 2008 TC3 the first asteroid that was documented before and after impact.
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- Unfortunately, the close passage of asteroid 2020 VT4 seems to have gone unwitnessed; closest approach occurred at 17:20 Universal Time (UT) on Friday November 13th over the South Pacific near the Pitcairn Islands under daytime skies, and it followed the edge of the Earth’s shadow outbound.
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- For context, the International Space Station also orbits 250 miles above the surface of the Earth, and is 358 feet long from tip-to-tip. 2020 VT4 would have certainly been visible as a fast-moving +3 magnitude ‘star’ on its out-bound leg south of Tasmania in the pre-dawn sky, had any island-bound observer or early morning sailor happened to be watching.
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- No satellites, including the ISS, which was over the South Atlantic at the time, were affected by the passage of 2020 VT4, though it certainly did plow through the sphere of geostationary satellites and graze the ring of low-Earth orbit.
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- Had it struck the Earth, 2020 VT4 would have simply put on a good show, and maybe left a meteorite strewn field in its wake. For context, the asteroid that produced the 2013 Chelyabinsk event was thought to have been 20-meters across.
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- This passage actually substantially altered the orbit of 2020 VT4. Inbound, the asteroid was on a 549-day orbit around the Sun, inclined 13 degrees relative to the ecliptic… its encounter with the massive Earth deflected it into a 315-day orbit inclined 10.2 degrees versus the ecliptic plane. With a perihelion now inside the orbit of Venus, this actually changes 2020 VT4’s classification from a NEO Apollo Earth-crosser, to an Aten asteroid.
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- 2020 VT4 will next visit the Earth on November 13th 2052 with a much more distant 0.02 AU (1.8 million mile, nominal) pass.
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- Will we get hit by an asteroid. Our the fate of the Universe be more about physics than astronomy? The fate of the universe strongly depends on a factor of unknown value: “O“, a measure of the density of matter and energy throughout the cosmos. If “O” is greater than 1, then space-time would be "closed" like the surface of an enormous sphere.
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- If there is no dark energy, such a universe would eventually stop expanding and would instead start contracting, eventually collapsing in on itself in an event dubbed the "Big Crunch."
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- If the universe is “closed” but there is dark energy, the spherical universe would expand forever.
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- Alternatively, if O is less than 1, then the geometry of space would be "open" like the surface of a saddle. In this case, its ultimate fate is the "Big Freeze" followed by the "Big Rip": first, the universe's outward acceleration would tear galaxies and stars apart, leaving all matter frigid and alone.
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- Next, the acceleration would grow so strong that it would overwhelm the effects of the forces that hold atoms together, and everything would be wrenched apart.
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- If O = 1, the universe would be flat, extending like an infinite plane in all directions. If there is no dark energy, such a planar universe would expand forever but at a continually decelerating rate, approaching a standstill. If there is dark energy, the flat universe ultimately would experience runaway expansion leading to the Big Rip. Regardless how it plays out, the universe is dying. “Que sera, sera“.
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- What is dark energy? The content of the universe? No matter how astrophysicists crunch the numbers, the universe simply doesn't add up. Even though gravity is pulling inward on space-time, the "fabric" of the cosmos, it keeps expanding outward faster and faster. To account for this, astrophysicists have proposed an invisible agent that counteracts gravity by pushing space-time apart. They call it dark energy.
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- In the most widely accepted model of “dark energy“, it is a "cosmological constant": an inherent property of space itself, which has "negative pressure" driving space apart. As space expands, more space is created, and with it, more dark energy.
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- Based on the observed rate of expansion, scientists know that the sum of all the dark energy must make up more than 70 percent of the total contents of the universe. But no one knows how to look for it.
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- What is dark matter? About 84 percent of the matter in the universe does not absorb or emit light. "Dark matter," as it is called, cannot be seen directly, and it hasn't yet been detected by indirect means, either. Instead, dark matter's existence and properties are inferred from its gravitational effects on visible matter, radiation and the structure of the universe.
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- This shadowy substance is thought to pervade the outskirts of galaxies, and may be composed of "weakly interacting massive particles," or WIMPs. Worldwide, there are several detectors on the lookout for WIMPs, but so far, not one has been found. One recent study suggests dark mater might form long, fine-grained streams throughout the universe, and that such streams might radiate out from Earth like hairs.
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- Why is there an arrow of time? The fact that you can't un-break an egg is a common example of the law of increasing entropy. Time moves forward because a property of the universe called "entropy," roughly defined as the level of disorder, only increases, and so there is no way to reverse a rise in entropy after it has occurred.
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- The fact that entropy increases is a matter of logic: There are more disordered arrangements of particles than there are ordered arrangements, and so as things change, they tend to fall into disarray.
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- The underlying question here is, why was entropy so low in the past? Put differently, why was the universe so ordered at its beginning, when a huge amount of energy was crammed together in a small amount of space?
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- Are there parallel universes? Astrophysical data suggests space-time might be "flat," rather than curved, and thus that it goes on forever. If so, then the region we can see (which we think of as "the universe") is just one patch in an infinitely large "quilted multiverse."
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- The laws of quantum mechanics dictate that there are only a finite number of possible particle configurations within each cosmic patch (10^10^122 distinct possibilities). So, with an infinite number of cosmic patches, the particle arrangements within them are forced to repeat, infinitely many times over. This means there are infinitely many parallel universes: cosmic patches exactly the same as ours as well as patches that differ by just one particle's position, patches that differ by two particles' positions, and so on down to patches that are totally different from ours.
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- Is there something wrong with that logic, or is its bizarre outcome true? And if it is true, how might we ever detect the presence of parallel universes?
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- Why is there more matter than antimatter? The question of why there is so much more matter than its oppositely-charged and oppositely-spinning twin, antimatter, is actually a question of why anything exists at all. One assumes the universe would treat matter and antimatter symmetrically, and thus that, at the moment of the Big Bang, equal amounts of matter and antimatter should have been produced.
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- But if that had happened, there would have been a total annihilation of both: Protons would have canceled with antiprotons, electrons with anti-electrons (positrons), neutrons with antineutrons, and so on, leaving behind a dull sea of photons in a matterless expanse.
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- For some reason, there was excess matter that didn't get annihilated, and here we are. For this, there is no accepted explanation. The most detailed test to date of the differences between matter and antimatter, announced in August 2015, confirm they are mirror images of each other, providing exactly zero new paths toward understanding the mystery of why matter is far more common.
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- Here is an even stranger concept. How do measurements collapse quantum wavefunctions? Performing a measurement on a particle collapses its wavefunction, causing it to assume one value for the attribute being measured. In the strange realm of electrons, photons and the other fundamental particles, quantum mechanics is law.
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- Particles don't behave like tiny balls, but rather like waves that are spread over a large area. Each particle is described by a "wavefunction," or probability distribution, which tells what its location, velocity, and other properties are more likely to be, but not what those properties are.
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- The particle actually has a range of values for all the properties, until you experimentally measure one of them (its location, for example) at which point the particle's wavefunction "collapses" and it adopts just one location.
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- But how and why does measuring a particle make its wavefunction collapse, producing the concrete reality that we perceive to exist? The issue, known as the measurement problem, may seem esoteric, but our understanding of what reality is, or if it exists at all, hinges upon the answer.
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- Is string theory correct? When physicists assume all the elementary particles are actually one-dimensional loops, or "strings," each of which vibrates at a different frequency, physics gets much easier. String theory allows physicists to reconcile the laws governing particles, called quantum mechanics, with the laws governing space-time, called general relativity, and to unify the four fundamental forces of nature into a single framework.
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- But the problem is, string theory can only work in a universe with 10 or 11 dimensions: three large spatial ones, six or seven compacted spatial ones, and a time dimension. The compacted spatial dimensions, as well as the vibrating strings themselves, are about a billionth of a trillionth of the size of an atomic nucleus. There's no conceivable way to detect anything that small, and so there's no known way to experimentally validate or invalidate string theory.
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- Finally: We end with chaos . . . Is there order in chaos? The equations that describe weather and water, among other things, have not been solved. Physicists can't exactly solve the set of equations that describes the behavior of fluids, from water to air to all other liquids and gases.
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- In fact, it isn't known whether a general solution of the so-called Navier-Stokes equations even exists, or, if there is a solution, whether it describes fluids everywhere, or contains inherently unknowable points called singularities.
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- As a consequence, the nature of chaos is not well understood. Physicists and mathematicians wonder, is the weather merely difficult to predict, or inherently unpredictable? Does turbulence transcend mathematical description, or does it all make sense when you tackle it with the right math?
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- Do the universe's forces merge into one? The universe experiences four fundamental forces: electromagnetism, the strong nuclear force, the weak interaction (also known as the weak nuclear force) and gravity. To date, physicists know that if you turn up the energy enough, inside a particle accelerator, three of those forces "unify" and become a single force.
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- Physicists have run particle accelerators and unified the electromagnetic force and weak interactions, and at higher energies, the same thing should happen with the strong nuclear force and, eventually, gravity.
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- Even though theories say that should happen, nature doesn't always oblige. So far, no particle accelerator has reached energies high enough to unify the strong force with electromagnetism and the weak interaction. Including gravity would mean yet more energy.
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- It isn't clear whether scientists could even build one that powerful; the Large Hadron Collider (LHC), near Geneva, can send particles crashing into each other with energies in the trillions of electron volts (about 14 tera-electron volts, or TeV). To reach grand unification energies, particles would need at least a trillion times as much, so physicists are left to hunt for indirect evidence of such theories.
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- Besides the issue of energies, Grand Unified Theories (GUTs) still have some problems because they predict other observations that so far haven't panned out. There are several GUTs that say protons, over immense spans of time (on the order of 10^36 years), should turn into other particles.
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- This has never been observed, so either protons last much longer than anyone thought or they really are stable forever. Another prediction of some types of GUT is the existence of magnetic monopoles, isolated "north" and "south" poles of a magnet, and nobody has seen one of those, either. It's possible we just don't have a powerful enough particle accelerator. Or, physicists could be wrong about how the universe works.
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- That is why we have students who can figure this stuff out in the future. We gave it our best shot but left a lot of work undone. Good luck the future is all yours. The past is all gone and the present does not exist but for an immeasurable instant.
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- November 22, 2020 2911
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