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Physics, Astronomy & Cosmology / Re: Can two protons differ in mass?

« on: 18/01/2019 00:13:03 »

Indeterminacy would apply equally to the mass of both particles, because the concomitant of indeterminacy is indistinguishability.

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Physics, Astronomy & Cosmology / Re: Has there always been a constant number of photons?

« on: 29/12/2018 17:57:08 »

Does the circumference of a circle with infinite radius equal a straight line?

No. See Cantor on multiple infinities.

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Physics, Astronomy & Cosmology / Re: Is there a detectable direction in which the universe is expanding?

« on: 20/12/2018 10:42:52 »

The Solar System (and our local galaxy cluster) seems to have a measurable motion with respect to the Cosmic Background Radiation. The CMBR seems to be slightly red-shifted in one direction, and slightly blue-shifted in the opposite direction.

Whether this represents random motion of our galaxy, a local gravitational concentration or a random temperature variation in the CMBR is not known for certain.

See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy

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Physics, Astronomy & Cosmology / Re: What does the term 'time' relate to in time dilation?

« on: 16/12/2018 22:25:37 »

Experience teaches that trying to forge any kind of link between this sort of mathematical concept and the “real world” leads nowhere. 

Far from it. A rigorous treatment of infintesimals leads to differential calculus, whence we get the whole world of classical physics, mesoscopic engineering and just about everything that distinguishes enlightened men from priests, politicians, philosophers and all the other human dross we scientists scrape off our shoes.

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Physics, Astronomy & Cosmology / Re: Would particles orbit a falling body?

« on: 17/11/2018 19:47:12 »

No, at that close to the Earth, even a steel marble would be within the Roche limit.   Tidal forces generated by the Earth would exceed the gravitational attraction of the marble. For a steel marble you would have to be at least 708 km above the surface for this to not to be the case. 

For objects to orbit the marble, they would have to be within the marble's Hill sphere. A 0.5 cm radius steel marble would have to be ~1689 km above the surface of the Earth in order for its Hill sphere radius to be larger than it own radius, so this is the closest it could be to the Earth and hold anything in orbit around itself.

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Physics, Astronomy & Cosmology / Re: What is needed to create new atoms in the Universe?

« on: 05/11/2018 08:16:56 »

the accretion disc temperature of the SMBH was 10 ^9 , and the temperature of a star's core is 10^6....
 A star at 10^6 is fusing hydrogen into helium. At a higher temperature (an accretion disk) would be fusing the heavier elements

I'm afraid not, because there is more to it than just temperature.

The Lawson Criterion describes three parameters that must be satisfied to get fusion going: density, confinement time, and plasma temperature.
- Density: The density at the center of the Sun is around 150 g/cm³, about 30 times denser than iron. An accretion disk is effectively in free fall, so it is not confined to such extreme densities
- Confinement Time: The Hydrogen from the Sun has been crushed in there for billions of years. Matter in the accretion disk around a black hole might reach maximum pressures for perhaps days or hours before being swallowed by the black hole or spat out in a polar jet.

The Lawson Criterion was applied originally to Hydrogen fusion, but the requirements for density, confinement time, and plasma temperature are even more extreme for fusion of heavier elements.
- There is an additional criterion: Raw materials. Since the universe has more hydrogen than anything else, accretion disks will probably also be dominated by hydrogen. There may not be enough of anything else to fuse much of it.

See: https://en.wikipedia.org/wiki/Lawson_criterion

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Physics, Astronomy & Cosmology / Re: How did scientists measure the mass of the Earth and other planets?

« on: 14/10/2018 09:37:33 »

from: alancalverd on 12/10/2018 09:49:23Using F = GmM/r2 you can calculate the force on a falling object of mass m in terms of M, the mass of the earth, and G, which we assume to be a universal constant.

That doesn’t work.  We’re trying to compute at least a rough G and M here.  We don’t know either of them yet.  We do know force F is 9.8 newtons for a 1KG mass.  We can assume we know r.  We therefore know the product of G and M, but not either separately.

We don't "know" F = 9.8 N/kg. We define the newton as1 kg.m.s^-2, and have a measured value of g = F/m

We don't "assume" r: it is a measured value - see below.

As I said, Cavendish (1797) measured G directly. 

Maskeleyne estimated the density of the planet from an experiment in 1774 at Schiehallion, measuring the deflection of a plumb bob on two sides of the mountain. In fact, that was a measure of G rather than ρ_earth since the assumption that the mountain was homogeneous was more defensible. Newton had considered the possibility but rejected the experiment as too difficult.

As F = ma, we can measure the acceleration of a falling object or the period of a pendulum to get a value for F/m

F=ma works (F 9.8 = 1 (mass) * 9.8 m/sec acceleration), but that doesn’t yield either mass of Earth M nor G, which are the two things we’re trying to determine here.
The pendulum thing is a function of acceleration (9., not of the mass of Earth.  Put a pendulum in a rocket accelerating at that rate and it will have the same period as here on Earth.  It tells you nothing about the mass of the Earth under you.

You have missed the point. If we know F/m we know GM/r², and we have known r since 200 BC (Eratosthenes), so all that was required for an accurate estimate of M was Cavendish's determination of G. The reason for using a pendulum  is that we know the period T = 2π√(Lm/F) for small oscillations, which is a simpler experiment than measuring the acceleration of an object in free fall.

The most amazing fact in all this, hundreds of years and thousands of experiments later,  is that the gravitational masses of all bodies are identical to their inertial masses. Why?

Interestingly, Hipparchus estimated the radius of the moon's orbit around 130 BC, though his assumptions regarding the earth's orbit of the sun were somewhat wild.

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Physics, Astronomy & Cosmology / Re: What's a black hole made of?

« on: 13/10/2018 01:17:54 »

The illuminous region around the BH's gravitational field represents it's external boundary

There is a region called the "photon sphere", which is outside the event horizon (at 50% greater radius). If you emitted a flash of light here, you would see a series of light echoes as photons from the flash repeatedly orbit the black hole.

Light emitted within the photon sphere eventually finds its way into the black hole.
By itself, the photon sphere does not emit any light, so you could not call this region "luminous".
However, matter in an accretion disk around a rotating black hole is subject to severe shear forces, which does emit a lot of light (including infra-red at the outer parts, and X-Rays at the inner edge).
See: https://en.wikipedia.org/wiki/Photon_sphere

The illuminous region around the BH's gravitational field represents ... is a reflection of the incoming light striking a mass.

If there is no infalling matter (eg from a closely-orbiting companion star) then there is no mass between the photosphere and the event horizon (...if you ignore the hypothetical, microscopically thin, microwave-shifted skin of star matter that fell into the event horizon when the black hole first formed).
For a black hole that is not actively consuming matter, there is no luminous region around it.

This reflection is similar to what occurs on a star, The cooler substrata below the star's surface creates a barrier that the hotter corona reflect off of. During a coronal () we see the cooler substrata mass.

I am not sure what "coronal" event you are talking about - maybe a Coronal Mass Ejection, or the Corona that is visible during an eclipse by the Moon?
But in any case, the density of the corona is so low, and the corona's total light output is so low that it is only visible from Earth's surface during a total solar eclipse. (Space telescopes can see it at other times using a coronagraph - but they don't need to battle Earth's atmosphere...)

Apart from solar eclipses, all that we see of the Sun is the lower layers of the Sun's atmosphere - the photosphere (not to be confused with the photon sphere around black holes!). We don't need to wait for some special coronal event to see it. The photosphere is not solid, and it tends to absorb light rather than reflect it.

The photosphere has almost a black body spectrum of around 5500C, overlain with fine emission and absorption lines from elements in the Sun. It does not reflect the spectrum of the corona (which has a temperature in the millions C).
See: https://en.wikipedia.org/wiki/Photosphere

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Physics, Astronomy & Cosmology / Re: What's a black hole made of?

« on: 07/10/2018 22:29:18 »

(A Black Hole) cannot be made of normal matter.  That part is wrong.  Normal matter of that mass cannot support its own weight, and breaks down even before the black hole forms.

I think it is just a matter of grammatical tense here.
- We see mechanisms that form black holes from normal matter when a star implodes and/or explodes.
- However, once this matter approaches the singularity, normal matter should be torn apart - it's not clear what the components would be (eg would they be outside the Standard Model?)
- And once it reaches the singularity, normal matter should be mashed together - it's not clear what the result would be
- But really, we can't say much about what happens inside the event horizon of a black hole

Is a BH empty? If it rotates, the answer needs to be no.

We expect that most black holes will form with the angular momentum of their parent star, accretion disk or galaxy.
It is theoretically possible for a black hole to have near-zero angular momentum:
- If there was a merger of two black holes with opposite and equal angular momentum.
- Or transiently, if the black hole was tearing off the atmosphere of a nearby star which was orbiting in the opposite direction to the direction of black hole rotation.
- But I expect that most black holes would have considerable angular momentum

The black hole, is a singularity, it is comprised of unattached subatomic particles

A black hole singularity in general relativity is where all of the particles end up at a single point; all paths entering the event horizon end up at the singularity.

Some theories of Quantum Gravity may allow some quantum fuzziness about the "single point".

But Quantum Gravity is not yet sufficiently mature to assert that "it must be composed of subatomic particles that are not congealed in a structure".

a chiralty gravitational effect

Gravitational waves are polarized.

Once 3 gravitational wave observatories were online, it was possible to detect the polarization of gravitational waves.

The first one was: https://en.wikipedia.org/wiki/GW170814

But I don't understand  "a chiralty gravitational effect".

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Physics, Astronomy & Cosmology / Re: Can the vacuum be affected by gravity?

« on: 23/09/2018 05:04:15 »

Yes. Recall Hawking Radiation.

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Physics, Astronomy & Cosmology / Re: Does gravity have an infinite range?

« on: 21/09/2018 12:12:38 »

Some random thoughts: The Big Bang theory suggests a period of Cosmic Inflation, where for a moment, space expanded faster than the speed of light.

Gravity travels at the speed of light (in a vacuum). So for the moment before Cosmic Inflation, all matter was in the gravitational field of all other matter. This situation did not hold after Cosmic Inflation, nor does it hold for parts of the universe that are now beyond our Visible Universe.

So I suggest that:
- All of the universe once felt the gravitational pull of the rest of the universe, back at the Big Bang
- This was possible because the universe was not infinite, right after the Big Bang
- The effects of gravitational events that occur today (like colliding black holes) will propagate outwards at the speed of light, but will never reach the edge of the universe, as that is a receding boundary. So in this sense, the effects of gravity will have an infinite range in the infinite future (but also an infinitely small effect)...

Caveats:
- I really don't understand unification of the 4 forces in the early stages of the Big Bang.
- I really don't understand how quantization of gravity will affect this

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Geology, Palaeontology & Archaeology / Re: To what extent can Biblical accounts of Noah's flood be believed?

« on: 20/09/2018 12:48:55 »

None of the stories in the old testament are to be taken as fact. My understanding is that when they were first written (over the course of multiple centuries, by different groups of people http://www.ancient-hebrew.org/articles_authors.html ), no one expected the stories to be taken literally (in fact the bible contradicts itself multiple times--allowing for much more complex analysis by the scholars--and contradicts physical possibility many times as well). Instead the stories are meant to be fables, and only in the centuries after the new testament did it become mainstream to believe that it actually happened exactly as it was written. (possibly due to the philosophical influences of christian and muslim schools of thought.)

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Physics, Astronomy & Cosmology / Re: What do strange quarks do?

« on: 13/09/2018 11:54:33 »

the neutron lifetime puzzle

I wondered why I kept seeing different figures for neutron lifetime.

Not the 9 second difference between beam and bottle experiments.

But the larger difference between half-life and mean lifetime...

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Physics, Astronomy & Cosmology / Re: What would a cold neutron star look like?

« on: 14/08/2018 23:20:42 »

create geometries very unlike such oxides at standard conditions

I agree that there will be crystal structures and molecules that would never be stable on Earth.

One unique thing that we don't have to worry about on Earth is that the gravitational potential energy on the surface of a neutron star is greater than the strength of mere chemical bonds. So elements would be sorted vertically by density. Chemical bonds would only be possible between atoms of very similar density.

The lightest element is hydrogen, and so it would be in the outer layer. Under these pressures hydrogen would probably form a metallic state, possibly superconducting?

A more speculative distorting factor is that the tidal forces and time dilation effects on the surface of a neutron star may be enough to distort the form of the electron's wave equation so that it takes on different forms than we have on Earth. What this would do to the interaction between light and matter is beyond me!

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General Science / Re: Has special relativity been refuted?

« on: 10/07/2018 17:57:00 »

But the apparent speed of the CMBR is the same no matter which way we look at it. Velocity differs from speed in that it includes a direction. It looks to me that your reasoning would indicate that we are moving away from the source of the CMBR at roughly 368 km/s, but because the source is all around us, that presents a paradox: in which direction are we moving 368 km/s?

Not quite
https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy

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Physics, Astronomy & Cosmology / Re: Is this formula valid?

« on: 07/07/2018 21:35:20 »

So what if we have the following formula?

Δλ = 2πγ/k

Can we introduce gamma to modify the wavelength due to relative velocity? Can this be a valid way of viewing orbitals?

No
Orbitals have three dimensional shapes and also odd properties that have to fit with the uncertainty principle.

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Physics, Astronomy & Cosmology / Re: The Graviton?

« on: 05/07/2018 21:46:55 »

However, real gravitons propagate away to infinity, as oscillations on the gravitational field. This is what LIGO detected. (And real photons propagate away to infinity, as oscillations on the electromagnetic field. This is what telescopes detect.)

LIGO detected gravitational waves as predicted by EFE not gravitons. Gravitons are theorized to exist and have such low energy levels that we can not detect them with todays technology.

If gravitons exist (Gravity can be explained with a quantum theory), then gravitational waves would consist of gravitons.

Bosons can not escape a BH, a graviton is a 2 spin boson how can it get out of a BH. A gamma ray cannot escape the event horizon of a BH and it has significantly more energy.

Gravitons can't,  but since gravity would be mediated by virtual gravitons, this is no different from the fact that photons can't escape a BH, yet a BH can have a charge and an electromagnetic field mediated by virtual photons.

Gravitational waves definitely exist gravitons might not exist, and might not have enough energy to escape a BH.

Gravitational waves can't escape a BH either (By this I mean that gravitational waves cannot get out from inside the event horizon anymore than electromagnetic waves can.)

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Just Chat! / Praise for Evan_au

« on: 28/06/2018 11:16:09 »

@evan_au  just received on the Naked Scientists Twitter:

Project STREET WISE
@wise_project 50m50 minutes ago

I really enjoy reading evan_au comments on the @nakedscientists forum! 🤖 #isotoperesearch

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Chemistry / Re: Is it possible to create a gelatinous metal?

« on: 26/06/2018 14:37:53 »

This may be of interest.
https://www.sciencedirect.com/science/article/pii/S0010854513000131

Interesting find, but I don't think it is directly relevant--the gelators discussed in the article contain metal atoms, but they are not metallic. Rather, they are organometallic or metal organic complexes (these are the sorts of compounds I study, though not for making gels).

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Physics, Astronomy & Cosmology / Re: Why is energy observer dependent?

« on: 24/06/2018 13:15:33 »

This states that L = V + U.

Correction. L = T - V, where T = Kinetic energy and V = Potential energy. If the potential is a velocity dependent one then the letter U is used. This is particularly important in electrodynamics.