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Could a planet made completely of water exist? - Worldbuilding Stack Exchange
To be clear what the properties of this water planet should be:

The planet is completely made out of water (that is, any non-water substance makes up a negligible amount of its mass). There may be a non-water atmosphere above, but there's no stone or metal center; the water goes down to the center.
Most or all of the water on the planet's surface is liquid (there may be polar ice caps, but they shall cover less than half of the planet).
The planet is held together by its own gravitation.
Is such a planet possible? And if so, could there be a plausible mechanism how it could be created naturally?
Science  Space  Planets  ScienceFiction  StarTrek  Water  Aqua  Gravity 
3 days ago by dk33per
The geometry that could reveal the true nature of space-time | New Scientist issue 3136, 29 Jul 2017
"The discovery of an exquisite geometric structure is forcing a radical rethink of reality, and could clear the way to a quantum theory of gravity"

[Andrew Hodges, one of Penrose’s colleagues at Oxford] "showed that the various terms used in the BCFW method could be interpreted as the volumes of tetrahedrons in twistor space, and that summing them up led to the volume of a polyhedron."

"So why invoke virtual particles at all? ... The first is that dealing with them rather than with fields makes the maths more tractable. The other great advantage is that they help physicists visualise everything as the well-defined interactions between point-like particles, as opposed to the hazy goings-on between particles and fields. This fits nicely with the intuitive principle of locality, which holds that only things in the same spot in space and time can interact. Finally, the technique also helps enforce the principle of unitarity, which says that the probability of all outcomes should add up to 1."

Gluon interactions seemed to complex, but "In 1986, Stephen Parke and Tomasz Taylor from Fermilab near Batavia, Illinois, used Feynman diagrams and supercomputers to calculate the likelihoods of different outcomes for interactions involving a total of six gluons. A few months later, they made an educated guess at a one-line formula to calculate the same thing. It was spot on. More than 200 Feynman diagrams and many pages of algebra had been reduced to one equation, and the researchers had no idea why."

"In 2005, Ruth Britto, Freddy Cachazo, Bo Feng and Edward Witten [BCFW] were able to calculate scattering amplitudes without recourse to a single virtual particle and derived the equation Parke and Taylor had intuited for that six-gluon interaction"

[Nima Arkani-Hamed and his team at IAS] "arrived at a mind-boggling conclusion: the scattering amplitude calculated with the BCFW technique corresponds beautifully to the volume of a new mathematical object. They gave a name to this multi-dimensional concatenation of polyhedrons: the amplituhedron."

"It may transform physics, too ... because the amplituhedron does not embody unitarity and locality, those core principles baked into reality as described by Feynman diagrams. ... If so, locality is not a fundamental feature of space-time but an emergent one."
NewScientist  geometry  physics  gravity  field-theory  quantum-mechanics  twistors  Mathematics  Roger-Penrose  Richard-Feynman  Ed-Witten 
21 days ago by pierredv
Twitter
#orbit #gravity #math #physics #moon #satellite https://t.co/pX5LMpwrgE
moon  math  orbit  physics  gravity  via:packrati.us  satellite 
4 weeks ago by mshook
Videos | Troll A Gas Platform (North Sea, 1995) | Structurae
Concrete gravity base structures | Videos | Troll A Gas Platform (North Sea, 1995) | Structurae Structure
architecture  video  building  offshore  technology  engineering  design  specifications  database  gravity  concrete 
5 weeks ago by asaltydog
New Satellite Experiment Helps Confirm Einstein's Equivalence Principle - Slashdot
Part of Einstein's theory of general relativity posits that gravity equals inertial mass -- and for the first time in 10 years, there's new evidence that he's right. Slashdot reader orsayman reports:
Most stories around space today seem to revolve around SpaceX, but let's not forget that space is also a place for cool physics experiments. One such experiment currently running into low orbit is the MICROSCOPE satellite launched in 2016 to test the (weak) Equivalence Principle (also knows as the universality of free fall) a central hypothesis in General Relativity.

The first results confirm the principle with a precision ten times better than previous experiments. And it's just the beginning since they hope to increase the precision by another factor of 10. If the Equivalence Principle is still verified at this precision, this could constrain or invalidate some quantum gravity theories. For those of you who are more satellite-science oriented, the satellite also features an innovative "self destruct" mechanism (meant to limit orbit pollution) based on inflatable structures described in this paper.
slashdot  physics  science  einstein  Gravity 
5 weeks ago by gardencat
How do you measure the mass of a star? (Beginner) - Curious About Astronomy? Ask an Astronomer
Measuring the mass of stars in binary systems is easy. Binary systems are sets of two or more stars in orbit about each other. By measuring the size of the orbit, the stars' orbital speeds, and their orbital periods, we can determine exactly what the masses of the stars are. We can take that knowledge and then apply it to similar stars not in multiple systems.

We also can easily measure the luminosity and temperature of any star. A plot of luminocity versus temperature for a set of stars is called a Hertsprung-Russel (H-R) diagram, and it turns out that most stars lie along a thin band in this diagram known as the main Sequence. Stars arrange themselves by mass on the Main Sequence, with massive stars being hotter and brighter than their small-mass bretheren. If a star falls on the Main Sequence, we therefore immediately know its mass.

In addition to these methods, we also have an excellent understanding of how stars work. Our models of stellar structure are excellent predictors of the properties and evolution of stars. As it turns out, the mass of a star determines its life history from day 1, for all times thereafter, not only when the star is on the Main Sequence. So actually, the position of a star on the H-R diagram is a good indicator of its mass, regardless of whether it's on the Main Sequence or not.
nibble  q-n-a  org:junk  org:edu  popsci  space  physics  electromag  measurement  mechanics  gravity  cycles  oscillation  temperature  visuo  plots  correlation  metrics  explanation  measure  methodology 
5 weeks ago by nhaliday
Two Stars Collided And Solved Half of Astronomy's Problems. Now What? - Slashdot
"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...?"
slashdot  stars  Astronomy  science  Gravity 
5 weeks ago by gardencat

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