Find out what black holes are, who discovered them, how we know they exist and what would happen if you fell into a black hole.

Nothing can go faster than light. It's a rule of physics woven into the very fabric of Einstein's special theory of relativity. The faster something goes, the closer it gets to its perspective of time freezing to a standstill.

Go faster still, and you run into issues of time reversing, messing with notions of causality.

But researchers from the University of Warsaw in Poland and the National University of Singapore have now pushed the limits of relativity to come up with a system that doesn't run afoul of existing physics, and might even point the way to new theories.

What they've come up with is an "extension of special relativity" that combines three time dimensions with a single space dimension ("1+3 space-time"), as opposed to the three spatial dimensions and one time dimension that we're all used to.

Rather than creating any major logical inconsistencies, this new study adds more evidence to back up the idea that objects might well be able to go faster than light without completely breaking our current laws of physics.

Structure of Water and Ice

Water is a covalent compound. It consists of two hydrogen atoms covalently bonded with the oxygen atom at the centre. In water molecule, the central atom goes SP3 hybridization. According to VSEPR theory, it should have tetrahedral structure but the presence of two lone pair of electron in oxygen increases the repulsion between the H atoms and its shape becomes distorted tetrahedral. The HOH bond angle decreases from 109.5o to 104.5o.

Due to the strong electronegative character of oxygen, water molecule is highly polarized. Therefore, there is a formation of intermolecular hydrogen bonding between oxygen of one molecule and hydrogen of another molecule. The extra energy is required to break this molecular bond. Due to this strong association between the hydrogen and oxygen, water molecules become liquid and solid at room temperature. In the absence of hydrogen bond, water would be in gaseous state as that of H2S. This is the reason for H2O being liquid at room temperature while H2S is gas at same temperature while both of the compounds have similar bonding. This is also the reason for anomalous behaviour of water.

Scientist studied that water molecules in ice are arranged in such a way that they form open cage like structure with vacant space due to hydrogen bonding as shown in figure below. With the vacant space, the volume of ice increases. So, as volume has inverse relation with density. Ice has lesser density in compared to water and hence float in water. The figure above shows the arrangement of molecules in ice and water respectively.

Kevin Duperret 2 years ago
America is moving towards the metric system, one inch at a time //

redbat1010 2 years ago
will not do it. Read Measuring America and it will explain to why it will never fully switch to metric. State DOT's have tried. and it always ends up back with the Survey foot. //

TheNewGreenIsBlue 4 days ago
@Adam Smith THIS! Few people actually get this. Metric beats imperial when converting between units, but in MOST day to day life, you don't care... even in the SAME vector. Do I REALLY need to know how many feet it is between New York and Washington? So... does it REALLY matter that there are n feet / mile? In Canada, highway exits put signs out as 1200m and 400m. In the US, they do ¾ mile and ¼ mile... and there may be a case for keeping the units the same for faster processing.

They're both JUST as understandable. //

Adam Smith 4 days ago
The thing is you almost never do any arithmetic in aviation where the units would matter. Thus it does not matter what units you use. You just know that your flight level is X or Y units, no matter. Also the different units may be safer because they also imply what is being measured or indicated. And the change over to metric would surely cause a lot of accidents before it would be through. So safety first.

Benji XVIArs Praetorianreplya day agoreportignore user
Veritas super omens wrote:
show nested quotes
Because their equations make remarkable predictions (about the future!) that hold true time and again against a plethora of different hypothesis postulated to break their equation.

Von Neumann wrote an interesting essay open-mindedly discussing how the concept of mathematical (and scientific) rigour has changed many times. He himself jokes that he had changed his mind about it three times!

So it’s worth noting that even the idea of what constitutes mathematical rigour can and does evolve.

As he points out, too, the prevailing view of physicists in the 20th century came to be that a theory was a good theory if it either unified a set of previously disparate laws, or made predictions outside of existing observations that were then empirically validated. ie the idea that “physical laws” or theoretical models answer the “why” questions in a deep philosophical sense does not feature. (Hence the famous video where Feynman lectures the interviewer for asking a “why” question about magnetism.) That mindset does not preclude inserting terms into models where necessitated by the empirical facts. The resulting equations are merely our best models. //

phred14Ars Praetorianet Subscriptorreplya day agoreportignore user
Voix des Airs wrote:

I can't tell if this post is for real or not (sorry if it isn't - but in these threads I can't always tell) but if it is then: No. It doesn't work like that. External shells have no gravitational effect.

One of our early exercises in calculus / physics was the Newtonian version of the same effect. Basically as you descend into the Earth (assuming even distribution - close enough) gravitational attraction from any mass at a greater radius than you cancels out. Shoots the Hollow Earth people all to pieces - in Freshman year.

Fermilab's TeVatron just released the best mass measurement of the W-boson, ever. Here's what doesn't add up.

The Standard Model, our most successful theory of elementary particles of all-time, has some very deep and intricate relationships between the properties of the different particles baked into it. Based on the measured properties of the other particles, the rest mass energy of the W-boson ought to be 80.35 GeV, but the latest results from the CDF collaboration reveal a value of 80.43 GeV, at a remarkable 7-sigma significance. This marks the first experimental particle physics result that disagrees with the Standard Model at such high significance. If there's no mistake, it could be our first clue to what lies beyond the known frontiers of physics.

In the entire history of science, no theory has been more successful, in terms of predictions matching the results of experiments and observations, than the Standard Model of particle physics. Describing all of the known elementary particles as well as three of the fundamental forces relating them ⁠— electromagnetism, the strong nuclear force, and the weak nuclear force ⁠— we’ve never once conducted an experiment whose results contradicted this theory’s predictions. Particle accelerators from Brookhaven to SLAC to LEP to HERA to Fermilab to the Large Hadron Collider have tried again and again, but have never once found a robust anomaly that’s held up to further scrutiny.

And yet, in a new paper published in the April 8, 2022 issue of Science, the Collider Detector at Fermilab (CDF) experimental collaboration just released their latest results, which offer the most precise measurements of the mass of one of those fundamental particles, the W-boson, ever. Although the Standard Model predicts its rest mass energy, exquisitely, to be 80.36 giga-electron-volts (GeV), the CDF collaboration instead found 80.43 GeV, with an uncertainty of just 0.0094 GeV attached to it. This represents a 7-sigma discrepancy from the Standard Model’s predictions: the most robust experimental anomaly ever seen. Here’s the science behind this incredible result, and what it means for the Universe.

The Standard Model is, in a nutshell, our modern theory of particle physics. It includes:

six flavors of quark with three colors each, along with their anti-quark counterparts,
three types of charged leptons and three types of neutral, left-handed leptons (the neutrinos), along with their anti-lepton counterparts,
the photon, which is the massless boson that mediates the electromagnetic force,
the eight gluons, which are the eight massless bosons that mediate the strong nuclear force,
the three weak bosons — the W+, the W-, and the Z — which have large masses and mediate the weak nuclear force,
and the Higgs boson, which is a scalar particles that couples to, and gives mass to, all particles that have a non-zero mass.
The Standard Model itself details the relationships between these various particles, such as what couples to and interacts with which other particles. However, there are some properties that can only be determined from measuring them, such as the masses of the individual fundamental particles.

One very important property that the Standard Model doesn’t give you wiggle-room for, however, is how the particles affect one another. If the top quark was much more massive than it is, for example, it would increase the mass of the proton, because the particles inside the proton couple to particles which also couple to the top quark. As a result, if you can measure the masses of all-but-one of the Standard Model particles, the rest of the Standard Model will tell you what that last particle’s mass ought to be.

Scientists found themselves working from home along with most everyone else when universities shut down in the face of the COVID-19 pandemic—including laboratories, posing a unique challenge for experimentalists in particular. That's how physicists from the University of Illinois at Urbana-Champaign (UIUC) found themselves casting about for experiments that could be done at home in the kitchen. The physicists ended up investigating the physics of cooking pasta—first conducting home experiments, then repeating those with greater precision in the lab once the university reopened.

Cooking instructions on most packaged dried pastas typically recommend an 8 to 10 minute cooking time, but it's an imprecise method that can result in a great deal of variation in the consistency of the cooked pasta. Among other findings, the UIUC physicists came up with a simple technique, using just a ruler, to determine when one's spaghetti is perfectly al dente, with no need for the time-honored tradition of throwing a cooked strand against the wall—although the latter arguably requires less setup. (And yes, horrified Italians, the tasting method works just fine too. But where's the fun in that?)

A paper on their findings has just been accepted for publication in the journal Physics of Fluids, and two of the authors presented the work at this week's meeting of the American Physical Society in Chicago.

There have been a surprisingly large number of scientific papers seeking to understand the various properties of spaghetti, both cooking and eating it—the mechanics of slurping the pasta into one's mouth, for instance, or spitting it out (aka, the "reverse spaghetti problem"). The most well-known is the question of how to get dry spaghetti strands to break neatly in two, rather than three or more scattered pieces.

"The last star will slowly cool and fade away. With its passing, the Universe will become once more a void, without light or life or meaning."
So warned the physicist Brian Cox in the recent BBC series Universe. The fading of that last star will only be the beginning of an infinitely long, dark epoch. All matter will eventually be consumed by monstrous black holes, which in their turn will evaporate away into the dimmest glimmers of light. //

let's take a look at how "material" – physical matter – first came about. If we are aiming to explain the origins of stable matter made of atoms or molecules, there was certainly none of that around at the Big Bang – nor for hundreds of thousands of years afterwards.

Q:

I have been wondering why only electrons revolve around protons instead of protons other way around. They have electrostatic force and I think mass factor has nothing to do here. Then why?

Electrons do not "revolve around" the nucleus. They have a probability to be found near the nucleus, and they have the property of angular momentum but you really should not imagine it as proper movement... –
Stian Yttervik
Sep 20 at 13:32

A:

NB: I interpreted the question to essentially mean, why do protons rather than electrons reside in nuclei?

Electrons repel each other with a Coulomb force that grows very large when they are close together. Protons also repel each other in the same way, but the difference is that protons are also attracted to each other and to neutrons by the even stronger strong nuclear force (since protons are made up of quarks that feel the strong force), which acts over short range (∼10−15

m) and thus can be bound into dense nuclei.

Electrons are point-like particles and not made up of quarks. They do not interact via the strong nuclear force and cannot be bound into dense nuclei.

The astronomical unit was defined to be exactly 149 597 870 700 meters in 2012, so it is no longer a measured value. In fact, it never was a measured value. It was instead a computed value, and it was computed rather strangely.

Prior to 2012, the astronomical unit was defined as the distance between the center of the Sun at which a tiny particle in an unperturbed circular orbit about the Sun would yield a value of exactly 0.0172020985 for the Gaussian gravitational constant. That value corresponds to the distance at which a tiny particle in an unperturbed circular orbit about the Sun would have an orbital angular velocity of 0.0172020985 radians per solar day. That value corresponds to an orbital period of 365.256898 days. That value, now called a Gaussian year, was based on measurements available to Gauss of the length of a sidereal year. (The currently accepted value of the sidereal year is 365.256363004 days of 86400 seconds each.)

This outdated value in the length of a sidereal year was one of the reasons the astronomical unit was given a defined value in 2012. There were other reasons. One is that that definition made the concept of the astronomical unit a bit (more than a bit?) counter-intuitive. With that definition, uncertainty in the computed value of astronomical unit depended on the ability of solar system astronomers to estimate the Sun's gravitational parameter (conceptually, the product of the Newtonian gravitational constant and the Sun's mass; in practice, a quantity that could be estimated directly as a consequence of models used to generate ephemerides) and the ability to measure time.

The ability to measure time (currently about one part in 1016
) has far outpaced the ability to estimate the Sun's gravitational parameter (currently less than one part in 1010). This means that if the 2012 change had not happened, the uncertainty in the astronomical unit would depend on the ability estimate the Sun's gravitational parameter, about three parts in 1011, or about 0.000000003%. That's a lot better than the 0.0000001% precision asked about in the question.

We don't even know everything we don't know – a fact that's been made evident in a new discovery. While running equations for quantum gravity corrections for the entropy of a black hole, a pair of physicists found that black holes exert pressure on the space around them.
Not much pressure, to be sure – but it's a finding that's fascinatingly consistent with Stephen Hawking's prediction that black holes emit radiation and therefore not only have a temperature, but slowly shrink over time, in the absence of accretion.
"Our finding that Schwarzschild black holes have a pressure as well as a temperature is even more exciting given that it was a total surprise," said physicist and astronomer Xavier Calmet of the University of Sussex in the UK.
"If you consider black holes within only general relativity, one can show that they have a singularity in their centres where the laws of physics as we know them must break down.
"It is hoped that when quantum field theory is incorporated into general relativity, we might be able to find a new description of black holes." //

the finding could have interesting implications for our attempts to square general relativity (on macro scales) with quantum mechanics (which operates on extremely small scales).
Black holes are thought to be key to this undertaking. The black hole singularity is mathematically described as a one-dimensional point of extremely high density, at which point general relativity breaks down – but the gravitational field around it can only be described relativistically.
Figuring out how the two regimes fit together could also help tp solve a really thorny black hole problem. According to general relativity, information that disappears beyond a black hole could be gone forever. Under quantum mechanics, it can't be. This is the black hole information paradox, and mathematically exploring the space-time around a black hole could help resolve it.

A science YouTuber has won a five-figure bet from a physics professor after he proved a wind-powered car could move faster than the wind while driving downwind.

Derek Muller, who runs the YouTube channel Veritasium, made the bet with Alexander Kusenko, a physics professor at the University of California, after Kusenko messaged him saying that it was impossible for the car to travel faster than the wind propelling it, according to Vice.

So Muller proposed a $10,000 wager with the professor saying that he could prove it. The pair signed an agreement to the bet, which was witnessed by Bill Nye and Neil deGrasse Tyson.

Thermoelectric (TE) conversion offers carbon-free power generation from geothermal, waste, body or solar heat, and shows promise to be the next-generation energy conversion technology. At the core of such TE conversion, there lies an all solid-state thermoelectric device which enables energy conversion without the emission of noise, vibrations, or pollutants. To this, a POSTECH research team proposed a way to design the next-generation thermoelectric device that exhibits remarkably simple manufacturing process and structure compared to the conventional ones, while displaying improved energy conversion efficiency using the spin Seebeck effect (SSE).

Two black holes; one very warped tango.

Black Hole

The main reasons given by people to explain why they hang their toilet paper a given way are ease of grabbing and habit.[11] Some particular advantages cited for each orientation include:

• Over reduces the risk of accidentally brushing the wall or cabinet with one's knuckles, potentially transferring grime and germs.[12]
• Over makes it easier to visually locate and to grasp the loose end.[13]
• Over gives hotels, cruise ships, office buildings, public places and homeowners with guest bathrooms the option to fold over the last sheet to show that the room has been cleaned.[14]
• Over is generally the intended direction of viewing for the manufacturer's branding, so patterned toilet paper looks better this way.[15]
• Under provides a tidier appearance, in that the loose end can be more hidden from view.[16][17]
• Under reduces the risk of a toddler or a house pet such as a cat unrolling the toilet paper when batting at the roll.[18]
• Under in a recreational vehicle may reduce unrolling during driving.[19] //

Advice columnist Ann Landers (Eppie Lederer) was once asked which way toilet paper should hang. She answered under, prompting thousands of letters in protest; she then recommended over, prompting thousands more.[47] She reflected that the 15,000 letters made toilet paper the most controversial issue in her column's 31-year history,[48] wondering, "With so many problems in the world, why were thousands of people making an issue of tissue?"[47]

In November 1986, Landers told the Canadian Commercial Travellers Association that "Fine-quality toilet paper has designs that are right side up" in the over position.[48] In 1996, she explained the issue on The Oprah Winfrey Show, where 68 percent of the studio audience favored over; Oprah suggested that under uses more paper.[49] In 1998, she wrote that the issue "seems destined to go on forever", insisting, "In spite of the fact that an overwhelming number of people prefer the roll hung so that the paper comes over the top, I still prefer to have the paper hanging close to the wall."[45] On the day of her last column in 2002, Landers wrote, "P.S. The toilet paper hangs over the top."[50]

When yanking at an angle in the "over" configuration, the straight segment of the toilet paper is tangent to the upper part of the roll before the yank, close to the point where the hole is resting on the axle. When yanking at an angle in the "under" configuration, the straight segment of the toilet paper is tangent to the lower part of the roll before the yank, far from the point where the hole is resting on the axle. As a result of the longer lever-arm, yanking at an angle in the "under" configuration applies a larger torque (hence a stronger tendency to spin the roll) compared to yanking at an angle in the "over" configuration, as observed in the experiment.

Earth generates heat. The deeper you go, the higher the temperature. At 25km down, temperatures rise as high as 750°C; at the core, it is said to be 4,000°C. Humans have been making use of hot springs as far back as antiquity, and today we use geothermal technology to heat our apartments. Volcanic eruptions, geysers and earthquakes are all signs of the Earth's internal powerhouse. //

The average heat flow from the earth's surface is 87mW/m2 – that is, 1/10,000th of the energy received from the sun, meaning the earth emits a total of 47 terawatts, the equivalent of several thousand nuclear power plants. The source of the earth's heat has long remained a mystery, but we now know that most of it is the result of radioactivity. //

The decay of one uranium-238 nucleus, for example, releases an average of 6 neutrinos, and 52 megaelectronvolts of energy carried by the released particles that then lodge in matter and deposit heat. Each neutrino carries around two megaelectronvolts of energy. According to standardized measures, one megaelectronvolt is equivalent to 1.6 10-13 joules, so it would take around 1025 decays per second to reach the earth's total heat. The question is, can these neutrinos be detected? //

Two recent experiments have added to the research: KamLAND, a detector weighing 1,000 metric tons underneath a Japanese mountain, and Borexino, which is located in a tunnel under the Gran Sasso mountain in Italy and weighs 280 metric tons. Both use "liquid scintillators." To detect neutrinos from the earth or the cosmos, you need a detection method that is effective at low energies; this means exciting atoms in a scintillating liquid. Neutrinos interact with protons, and the resulting particles emitted produce observable light.

KamLAND has announced more than 100 events and Borexino around 20 that could be attributed to geoneutrinos, with an uncertainty factor of 20-30%. We cannot pinpoint their source, but this overall measurement—while fairly rough—is in line with the predictions of the simulations, within the limits of the low statistics obtained.

Therefore, the traditional hypothesis of a kind of nuclear reactor at the center of the earth, consisting of a ball of fissioning uranium like those in nuclear power plants, has now been excluded. Fission is not a spontaneous radioactivity but is stimulated by slow neutrons in a chain reaction.

The National Academies report links high-power microwaves to impacts on people through the Frey effect. The human head acts as a receiving antenna for microwaves in the low gigahertz frequency range. Pulses of microwaves in these frequencies can cause people to hear sounds, which is one of the symptoms reported by the affected U.S. personnel. Other symptoms Havana syndrome sufferers have reported include headaches, nausea, hearing loss, lightheadedness and cognitive issues.

Q: As we all know, atomic clocks are being used to measure time and the GPS system. But I was wondering based on what was the first atomic clock calibrated and how accurate this calibration was based on our standards nowadays?

A: More specifically, caesium atomic clocks realize the second (see this Q&A for the meaning of realization) or, said another way, they are a primary frequency standard. Generally, when a new primary standard is being developed—for whatever quantity, not only time—and has not yet become, by international agreement, a primary standard, it should be calibrated against the primary standards of the time.

[...]

Pfizer's new vaccine has to be stored at extremely low temperatures. Here's how things work when it gets that cold.