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Two Stars Collided And Solved Half of Astronomy's Problems. Now What? (fivethirtyeight.com)
"It's hard to overstate the enormous leap forward that astronomy took on August 17, 2017," reports an article shared by schwit1:
On that day, astronomers bore witness to the titanic collision of two neutron stars, the densest things in the universe besides black holes. In the collision's wake, astronomers answered multiple major questions that have dominated their field for a generation. They solved the origin of gamma-ray bursts, mysterious jets of hardcore radiation that could potentially roast Earth. They glimpsed the forging of heavy metals, like gold and platinum. They measured the rate at which the expansion of the universe is accelerating. They caught light at the same time as gravitational waves, confirmation that waves move at the speed of light. And there was more, and there is much more yet to come from this discovery... "Now it's a question of, do we have the right instrumentation for doing all the follow-up work?" said Edo Berger, an astronomer at Harvard who studies explosive cosmic events. "Do we have the right telescopes? What's going to happen when we have not just one event, but one a month, or one a week -- how do we deal with that flood...?"
The August 17 gravitational wave gave astronomers a glimpse at an entirely different universe. For most of history, they've studied stars and galaxies, which seem static and unchanging from the vantage point of human timescales... But GW170817 revealed a universe alive, pulsating with creation and destruction on human timescales... [T]he event itself unfolded in less than three human-designated weeks. This faster timescale is "pushing the way astronomy is done," Berger said... In space, the Fermi space telescope glimpsed a burst of gamma radiation. Within an hour, astronomers made six independent discoveries of a bright, fast-fading flash: A new phenomenon called a kilonova... Nine days later, X-rays streamed in, and after 16 days, radio waves arrived, too. Each type of information tells astronomers something different. Richard O'Shaughnessy, an astronomer at the Rochester Institute of Technology, describes the discovery as a "Rosetta stone for astronomy."
"What this has done is provide one event that unites all these different threads of astronomy at once," he said. "Like, all our dreams have come true, and they came true now..." Thanks to the August 17 event, astronomers now know what to look for. Soon, they will be able to sift through an embarrassment of neutron-star mergers and other phenomena... And they are talking about how to turn their eyes to the sky, at a moment's notice, the next time the universe throws something big their way. "It's a wonderful time, it's a terrifying time," O'Shaughnessy said. "I can't really capture the wonder and the horror and glee and happiness."
The August 17 gravitational wave gave astronomers a glimpse at an entirely different universe. For most of history, they've studied stars and galaxies, which seem static and unchanging from the vantage point of human timescales... But GW170817 revealed a universe alive, pulsating with creation and destruction on human timescales... [T]he event itself unfolded in less than three human-designated weeks. This faster timescale is "pushing the way astronomy is done," Berger said... In space, the Fermi space telescope glimpsed a burst of gamma radiation. Within an hour, astronomers made six independent discoveries of a bright, fast-fading flash: A new phenomenon called a kilonova... Nine days later, X-rays streamed in, and after 16 days, radio waves arrived, too. Each type of information tells astronomers something different. Richard O'Shaughnessy, an astronomer at the Rochester Institute of Technology, describes the discovery as a "Rosetta stone for astronomy."
"What this has done is provide one event that unites all these different threads of astronomy at once," he said. "Like, all our dreams have come true, and they came true now..." Thanks to the August 17 event, astronomers now know what to look for. Soon, they will be able to sift through an embarrassment of neutron-star mergers and other phenomena... And they are talking about how to turn their eyes to the sky, at a moment's notice, the next time the universe throws something big their way. "It's a wonderful time, it's a terrifying time," O'Shaughnessy said. "I can't really capture the wonder and the horror and glee and happiness."
well a couple years old. but that's old in gravity
One of the great results of this flood of unified information, is that it seems like it may help a lot in analyzing previously collected data - either looking for particular events or knowing how to filter out some cosmic noise that may be obscuring other things.
The most exciting thing long term to me, is a better ability to determine in the end what might be the most appealing interstellar targets to send manned or unmanned craft to explore. I'll be long gone but it's nice to think about.
"There is more worth loving than we have strength to love." - Brian Jay Stanley
A neutron star has a density of roughly 1e14 gm/cm^3.
A black hole the mass of the earth would have a radius of about 9mm and a density of about 2e27, ten trillion times denser than a neutron star.
A black hole the mass of the sun would have a radius of about 3 km, and a density of about 1.8e16, a hundred times denser than a neutron star.
A black hole with the mass of our galaxy would have a radius of about 0.2 lightyears, and a density less than air.
A black hole with the mass of the known universe would have a radius of 13.7 billion lightyears, and a density far less than the highest vacuum that humans have ever produced.
A black hole with the mass of the known universe would have a radius of 13.7 billion lightyears
...so, the radius of the observable universe ! Is there some deeper meaning to this or is that just a coincidence ?
Non-Linux Penguins ?
In the collision's wake, astronomers answered multiple major questions that have dominated their field for a generation
So the scientists have "solved" half of their research questions.
If I was an astrophysicist I would be rather worried about my future job prospects at that announcement. Though I would be more concerned with the sloppy science behind doing a single experiment and assuming that every next time it repeats, the results will be the same.
I would be fervently hoping that the next time there is a neutron star collision, the data that comes in is very, very, different. Thus showing that all this conjecture means we don't really understand those "major questions", after all. Predictable science is so very dull.
politicians are like babies' nappies: they should both be changed regularly and for the same reasons
...so, the radius of the observable universe ! Is there some deeper meaning to this or is that just a coincidence ?
It is not likely a coincidence. As an object approaches a blackhole's event horizon, any light it emits undergoes a redshift, and the wavelength gets longer and longer the closer it gets. As it crosses the event horizon, the wavelength goes to infinity, and it is no longer observable. This is exactly what also happens at the edge of the observable universe. If the Schwarzschild Radius of the universe was larger, then we should be able to see further out, and the observable universe would be larger as well.
A bit of googling with DuckDuckGo dug up this
https://www.insidescience.org/...
A 1960s adaptation of general relativity, called the Einstein-Cartan-Sciama-Kibble theory of gravity, takes into account effects from quantum mechanics. It not only provides a step towards quantum gravity but also leads to an alternative picture of the universe. This variation of general relativity incorporates an important quantum property known as spin. Particles such as atoms and electrons possess spin, or the internal angular momentum that is analogous to a skater spinning on ice.
In this picture, spins in particles interact with spacetime and endow it with a property called "torsion." To understand torsion, imagine spacetime not as a two-dimensional canvas, but as a flexible, one-dimensional rod. Bending the rod corresponds to curving spacetime, and twisting the rod corresponds to spacetime torsion. If a rod is thin, you can bend it, but it's hard to see if it's twisted or not.
Spacetime torsion would only be significant, let alone noticeable, in the early universe or in black holes. In these extreme environments, spacetime torsion would manifest itself as a repulsive force that counters the attractive gravitational force coming from spacetime curvature. As in the standard version of general relativity, very massive stars end up collapsing into black holes: regions of space from which nothing, not even light, can escape.
Here is how torsion would play out in the beginning moments of our universe. Initially, the gravitational attraction from curved space would overcome torsion's repulsive forces, serving to collapse matter into smaller regions of space. But eventually torsion would become very strong and prevent matter from compressing into a point of infinite density; matter would reach a state of extremely large but finite density. As energy can be converted into mass, the immensely high gravitational energy in this extremely dense state would cause an intense production of particles, greatly increasing the mass inside the black hole.
The increasing numbers of particles with spin would result in higher levels of spacetime torsion. The repulsive torsion would stop the collapse and would create a "big bounce" like a compressed beach ball that snaps outward. The rapid recoil after such a big bounce could be what has led to our expanding universe. The result of this recoil matches observations of the universe's shape, geometry, and distribution of mass.
In turn, the torsion mechanism suggests an astonishing scenario: every black hole would produce a new, baby universe inside. If that is true, then the first matter in our universe came from somewhere else. So our own universe could be the interior of a black hole existing in another universe. Just as we cannot see what is going on inside black holes in the cosmos, any observers in the parent universe could not see what is going on in ours.
The motion of matter through the black hole's boundary, called an "event horizon," would only happen in one direction, providing a direction of time that we perceive as moving forward. The arrow of time in our universe would therefore be inherited, through torsion, from the parent universe.
Torsion could also explain the observed imbalance between matter and antimatter in the universe. Because of torsion, matter would decay into familiar electrons and quarks, and antimatter would decay into "dark matter," a mysterious invisible form of matter that appears to account for a majority of matter in the universe.
Finally, torsion could be the source of "dark energy," a mysterious form of energy that permeates all of space and increases the rate of expansion of the universe. Geometry with torsion naturally produces a "cosmological constant," a sort of added-on outward force which is the simplest way to explain dark energy. Thus, the observed accelerating expansion of the universe may end up b
echo -e 'global _start\n _start:\n mov eax, 2\n int 80h\n jmp _start' > a.asm; nasm a.asm -f elf; ld a.o -o a;
Right
Right - mostly. Though things like Hawking radiation can "escape", and there may be geometric oddities that allow information to escape as well
Getting iffy - it's not altogether clear that the "inside" of a black hole even exists to begin with - some theories have all inflow stop at the the event horizon itself, from where it could theoretically escape. All we know about the "inside" of a black hole, is that normal physics doesn't work there.
Nope - you're assuming our universe is a black hole or otherwise has an event horizon.
Nope - one of the defining qualities of (many classes) of alternate universes is that they have fundamentally different physics.
Nope.
Well,it depends on the *specific* multiverse theory you're referring to. There are a *lot* of different multi-universe theories, and many of them may be true simultaneously, giving rise to several fundamentally different classes of alternate universes.
Some are indeed a little "unscientific" in the sense that they could not be directly tested - such as the idea that our universe is one bubble among countless that formed during the inflationary phase of the universe, in which case (barring FTL) we can never contact any others, because we're all sharing the same coordinate system, and the boundaries of all our universes are expanding at almost lightspeed, while the space between them is still inflationary and expanding much faster than light. We could however conceivably create a "child universe" based on the same principles - though doing so would essentially create a new big bang, destroying everything in the observable universe as the new one expanded at light speed converting false-vacuum to new mass-energy. There's also the possibility that we could detect the "fingerprints" of early shockwaves within such a primordial bubble universe, which would validate the theory, but not provide any mechanism for inter-universe contact. I.E. the theory could be validated, but still be useless.
Many other theories postulate that our 4-dimensional universe is embedded in a multi-verse with a higher-order geometry, and that other universes (4-D or otherwise) are likewise embedded. Picture many sheets of infinitely thin paper floating in a pond as an analog for 2D universes in a 3D multiverse. In which case contact between such universes are theoretically possible if we could figure out a way to send signals in directions we're not yet aware of. Impossible to test today, but not fundamentally unscientific. And unlike universes which exist within the same 4D-space as ours and thus must lie somewhere beyond the bounds of the observable universe, parallel universes might be arbitrarily close. In fact, there's currently work being done to look for evidence of our universe colliding with others - an event which could occur anywhere in our universe since unlike the edges of a bubble universe, higher-order edges are omni-present.
--- Most topics have many sides worth arguing, allow me to take one opposite you.