1

The Environment / Re: Why do clouds stay high up when they are heavier than air?

« on: 08/10/2019 17:47:50 »

Is a cloud gaseous water or condensed water?

yes


The boundary of the cloud is not a true edge: water is going in and out of the cloud all the time. But only within the region of the cloud is the aerosol stable. Any water outside of the cloud is either in the gaseous state, or is precipitations (solid or liquid).

A good example of this is the lenticular cloud that can form on the leeward side of a mountain.  The wind pushes humid air up the windward slope which condenses on the leeward side.  The cloud formed remains in position with respect to the mountain, but the moisture forming it is constantly being removed by the wind, as the same wind brings in new moisture.

2

Physics, Astronomy & Cosmology / Re: Are gravitational waves faster than light?

« on: 24/09/2019 18:19:46 »

I know not of the podcast in question, but an event like a supernova has the light being delayed by the shock wave needing to travel to the surface of something like a star going supernova.  The light is also not subsequently traveling in a vacuum.  Gravity waves on the other hand are unimpeded by any of this and get here first.  So do neutrinos, which don't even travel at light speed, but fast enough that light (given the initial delay) never manages to catch up.

3

The Environment / Re: Why are the suns rays hot some days and not others?

« on: 20/09/2019 10:12:22 »

If you consider the elevation of the sun, rays have a lot more atmosphere to pass through in winter, hence greater absorption of IR.
Also, if you consider the energy/m² in a plane perpendicular to the rays then consider the angle of ground relative to the rays you will see that the energy is spread out over a greater area in winter reducing the heating, and hence air temperature, next to the ground.
Obviously, if you are standing then you are closer to the ray perpendicular, in which case the distance through atmosphere has greater effect.

4

Chemistry / Re: What is the most dangerous group of elements?

« on: 19/09/2019 20:18:03 »

FFS!
What is it about SF6 that makes otherwise reasonable people- even scientists- forget basic science.

This is a pretty dense gas - how well would it mix into the stratosphere?

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/properties2.html

"Gases have three characteristic properties: (1) they are easy to compress, (2) they expand to fill their containers, and (3) they occupy far more space than the liquids or solids from which they form."

5

Physics, Astronomy & Cosmology / Re: Is there an equivalent of absolute zero when it comes to heat?

« on: 19/09/2019 14:35:52 »

Is the concept of an absolute, approachable but unattainable 0 any less ridiculous?

That’s more interesting than it looks, at first glance.  HUP tells us why we can’t reach 0K; is there a similar principle/law that tells us why we can’t reach infinity?  What about HUP?  I suspect, not, but I’m no expert.

"Infinite" is not a number…..

I think this might have something to do with it. 

6

Chemistry / Re: Why doesn't water burn?

« on: 19/09/2019 00:25:25 »

'Burning' is actually a redox process.
The hydrogen and oxygen in water are fairly stable redox wise, but only in comparison to other natural compounds.
Thanks to this, the oceans aren't literally on fire.
However, strong oxidizers do, in effect, 'burn' water.
A dramatic example is chlorine trifluoride: ClF₃, CAS 7790-91-2.
Upon contact with water (or almost anything else), violent reaction occurs.

TL;DR:
Anything can burn with the right incentive.

Note: I wanted to embed a good youtube vid showcasing the stuff, but can't link currently. Look up Chlorine Trifluoride - it's fun!

7

Physics, Astronomy & Cosmology / Re: Could LIGO "see" alien warp technology?

« on: 01/09/2019 23:56:45 »

Oops! Overlap with Colin2B...
It's a bit hard to say, given that we know of no practical way to make such a warp drive.
- Some estimates have put the amount of mass/energy to create an Alcubierre drive at greater than the mas/energy of the universe
- That would certainly have an impact on the Earth if someone built one here.....

But if there were some practical way of creating such a drive
- And that it did radiate gravitational waves
          - Just like a supersonic plane radiates shock waves
          - This would be a continual power drain on the drive
          - I imagine designers would try to minimize wasted energy
- And the gravitational waves had a component in the right frequency range (about 50Hz to 1kHz for LIGO)
- Then it might be possible to detect it

I imagine that gravitational waves from a passing spaceship:
- Would be stronger, the closer the ship was
- Would be a single or double "blip" (like a supersonic shockwave), not the multiple cycles of oscillation that is currently being dredged out of the noise by the algorithms examining LIGO/VIRGO data.
- As a blip, it would have relatively little energy in the 50Hz-1kHz range
- But I imagine that different algorithms could search for coincident blips in the LIGO/VIRGO data

Future large gravitational wave detectors like eLISA (1 million km arms) would be even less sensitive to short "blips":
- A detector is most sensitive to frequencies whose arm length is about half a wavelength.
- Wavelengths much shorter than the arm length will have multiple cycles in the measurement arm (almost cancelling each other out)
- Wavelengths much longer than the arm length will have only a small part of a cycle in the measurement arm (dropping below the low-frequency response of the detector)

But if aliens had a warp drive, where are they? (Fermi's Paradox)

8

Chemistry / Re: What to catalyses do?

« on: 30/08/2019 10:26:23 »

Do you know what a jig is?  Have you ever had to assemble a collection of the same objects, over and over?

It gets boring and time consuming to assemble the same thing over and over.   SO...we build a jig.

We will place all the components in the jig......then with one operation.......one lever pull or a crank.....and the object is assembled.

The assembly device is called a jig.

A catalyst is a chemical jig.  It "fits" the components.

9

Science Experiments / Re: How can I calculate mass from a concentration/time graph?

« on: 05/08/2019 19:38:08 »

What does 1M mean in this?

goes to 1M when time = 1 hour.

10

Chemistry / Re: Making aluminum powder using angle grinder and aluminum profiles from windows?

« on: 26/06/2019 19:41:54 »

Essentially anything other than sand, glass, and concrete can be considered flammable under these situations.

and even they react...
https://ceramics.onlinelibrary.wiley.com/doi/abs/10.1111/j.1151-2916.1967.tb15049.x

Alumina is immune to the attack, but, unless you have plenty of it, it will melt.

11

New Theories / Re: How will buckyballs fired at a double slit behave?

« on: 17/06/2019 19:12:31 »

Atoms bouncing off each other collapses their waves.

That doesn't even parse.

There's something you need to understand.
It has already been pointed out, but you have missed it.
Imagine making a grating with a gap between the "wires" that's a little bit smaller than the molecules you are using.

Classically, no particles will get through it.

QM and the uncertainty principle means that a few will. They will quantum tunnel through.

Here's the bit you don't understand.
If you take the grating and hammer it until the wires are squashed flat and there are no gaps so it becomes a metal foil then repeat the experiment...

More atoms will get through the foil even though it no longer has gaps in it. (In some circumstances)

Do you understand that?
 The probability of tunneling is related to the thickness of the barrier.
Hammering it flat makes it thinner and so it's more likely that atoms will tunnel through.

Obviously, with the grating destroyed, there's no diffraction pattern.

And the (smaller number of) atoms that went through the grating before  you hammered it flat would also show no clear diffraction pattern because, at that level, the atoms are not going through the gaps.

It's the same , classically, with light
You know the equation
d sin θ =  λ
Where lambda is the wavelength and d is the spacing
you can rewrite that as

sin θ =  λ /d
Well, if you make d smaller than lambda then you are trying to find an angle where sin theta is more than 1, but that's impossible.

Diffraction doesn't work if the wavelength is bigger  than the grating's spacing.
And, returning to QM, a particle can't be "smaller" than the associated wavelength.

So, you can't sensibly calculate a diffraction pattern for the the experiment you have proposed.

So there's no way to say whether the particles would follow it or not.
And, as has been pointed out before, you also can't measure it because, in practice big  things don't go through small holes.

12

Physics, Astronomy & Cosmology / Re: Is there remote sensor for pH?

« on: 05/03/2019 18:51:33 »

Heather doesn't grow well on alkaline soils, so here's a very rough map of pH of the UK
http://www.moorlandassociation.org/wp-content/uploads/2015/03/Heather-coverage-UK.png

13

Chemistry / Re: What happens during electrolysis of salt water with gold and copper electrodes?

« on: 02/03/2019 18:13:43 »

Wet chlorine will oxidise gold.

The rate will be dependent on things like concentration and temperature (as well as the presence of other ions like chloride)

14

Physics, Astronomy & Cosmology / Re: Do you think Tau Ceti e is inhabited?

« on: 10/02/2019 18:58:47 »

Call it 99%. 99% of 150° is  148.5°.

Sorry to be the pedant, but are you scaling a temperature? In ° F?!?

150° F

At the very least, please use an absolute temperature scale (Kelvin or Rankine) before multiplying temperatures by any factor, otherwise we end up with such silly results, like: "50% hotter than 32 °F (0 °C) is 48 °F (8.9 °C), but 50% hotter than 0 °C is, still 0 °C?" or even worse: "50 % hotter than 20 °F (–6 °C) is 30 °F (–1.1 °C)..."

Even with absolute temperatures, scaling is somewhat nonsensical, but at least the maths work out.

Yeah your right.  Silly mistake on my part.


  Using the same numbers gives ~ 144° F.  For difference of 6°F.  But then again, I was being generous with the 99% estimate.   At the highest resolution of the graph in the paper, you might get 99% of circular orbit equilibrium temp at an eccentricity of 0.4, better than twice the eccentricity of Tau Ceti e, and its on a curve that flattens out as you approach 0 eccentricity. 

So despite my embarrassing lapse, I still don't think that this is enough to significantly increase the chances of Tau Ceti e being habitable

15

General Science / Re: Are there aliens made of lava?

« on: 14/01/2019 19:18:23 »

A section of the textbook Life in the Universe: Expectations and Constraints by Dirk Schulz-Makuch and Louis N. Irwin does go into this subject matter. Here's a quote from chapter 6:

Feinberg and Shapiro (1980) suggested that the existence of lavobes, organisms that could exist in lava flows, and magmobes, organisms that could exploit thermal gradients or chemical energy sources within the molten rock. These organisms could make use of the chemical complexity of silicate rocks in which aluminum could replace silicon in the tetrahedrons and cation exchange reactions could occur in interlayer sites between the tetrahedral and octahedral sheets. For this to occur, silicates would have to be in the form of sheets, such as the clay minerals smectite and montmorillonite. Information could be represented as irregularities in the crystal lattice of minerals. A particularly intriguing example is the clay mineral amesite, which has a helical structure. Information could be encoded by substitution of silicon with aluminum.

It goes on later to say:

However, given the environmental conditions of Earth's crust and its composition (46% oxygen, 28% silicon) with abundant silicate melts, Earth should be more favorable than most other planets and moons in our Solar System for such a form of life. Yet no fossilized remnants or structures consistent with such an organism have been found, even though outcrops of igneous and volcanic rocks are abundant. Thus, the existence of such organisms seems very unlikely.

16

Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 06/01/2019 08:35:41 »

In this perfect reverse universe with all the photons magically heading back to the sun

The trick of reversing time, and seeing if it makes sense says:
- Q1: If the Solar System were reversed in time, would the planetary orbits look normal?
- A1: Yes, The planetary orbits would look pretty normal.
          But if you looked closely at the orbit of the Moon, spiralling inwards is not normal, since tides dissipate energy as heat; the Moon should spiral outwards.

- Q2: If the Sun were reversed in time, would it look normal?
- A2: No, this would look very abnormal. Photons from across our galaxy (and beyond) do not spontaneously fly back towards the Sun. Heat does not spontaneously move from cooler places (the visible surface of the Sun) to hotter places (the center of the Sun). Helium does not spontaneously break down into Hydrogen. 

- Q3: If the Earth were reversed in time, would it look normal?
- A3: No, this would look rather abnormal. Heat does not spontaneously move from cooler places (the surface of the Earth) to hotter places (the center of the Earth). Cows do not regurgitate grass. Grass does not emit photons, turning complex chemicals like chlorophyl into carbon dioxide, water and nitrates. Random vibrations of the entire Earth's crust do not synchronise and converge at a point and move huge blocks of the Earth's crust.   

So parts of this macroscopic universe like the orbits of the planets are (close to) ideal, lossless, reversible systems.
But other parts like the Sun and the Earth have a clear direction to time's arrow, as dictated by entropy, and are clearly not reversible.

A Feynman diagram is time reversible

I agree that some simple Feynman diagrams with just 2 interacting real particles can be ambiguous in the direction of time.

But I suggest that by the time you get to the interaction of 3 or more real particles, a Feynman diagram provides a pretty clear idea of the direction of time (but not an absolute guarantee).

Take the decay of a neutron in a vacuum:
n⁰ → p⁺ + e⁻ + ν_e + 0.78MeV

1) The right hand side has 3 real particles which exist at the same time. The odds against these particles just happening to come together in the same place at the same time in a vacuum to form a neutron is so unlikely that it gives a clear direction to time's arrow.

2) The reaction releases 0.78MeV of energy, which is randomly split up amongst the products, and heads off in 3 different directions into the universe. Energy does not spontaneously gather from different parts of the universe and combine at a single point. This gives a clear direction to time's arrow.

See: https://en.wikipedia.org/wiki/Free_neutron_decay
This link shows a Feynman diagram for this reaction (with an arrow of time...)

17

Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 05/01/2019 07:53:07 »

In spite of the presence of the word “tends”, the assertion “it never decreases” can still be found attached to many explanations.

If you have a small system, like the 4 coins mentioned by ChiralSPO, then entropy will (sometimes) decrease back to the original 4H. But it will be somewhat uncommon - the most common occurrence would be to have 2H + 2T, with other combinations being less common.

If you have a larger system, like 1 million coins, the most common combination (after allowing a few million flips for it to stabilise) will be around 500,000H+500,000T; combinations like 1,000,000H will almost never occur.

Now turn that into something practical that you can pick up with your hand, like 6x10²³ atoms, and you can say that returning to the original state will practically never occur. Hence the use of the emphatic "never".

It is possible to manually flip all the coins back to the original all-H state, but this takes information and hence energy. So you can reduce entropy by expending energy, but left to itself, entropy tends to increase in macroscopic systems (at any temperature above absolute zero).

18

Physics, Astronomy & Cosmology / Re: Could Oumuamua be a light sail?

« on: 10/11/2018 20:36:19 »

How do we know what shape it is? From what I heard at the time, all they had was a regular brightening and darkening as it rotated, suggesting that we were getting more light from it when it's side on and less when it's end on, but it could simply be round with two bright spots on opposite sides.

19

General Science / Re: Why is the atmosphere transparent to CO2 lasers?

« on: 30/09/2018 16:35:22 »

The object of laser weapons is to deliver a huge amount of energy in a short pulse, to cause failure by adiabatic heating of the target. Most work has been done with carbon dioxide lasers because they are easy to make up to very large sizes, and considerably more efficient than most other solid or gas lasers. Nobody seems to have told the military that atmospheric carbon dioxide has a strong enough infrared absorption to destroy the earth's climate, and they just go on merrily shooting down drone targets, oblivious to the facts of global warming enthusiasts, which clearly prove that they can't work.

Thank you for clarifying your lack of understanding.
When a molecule in a CO2 laser emits radiation it falls to a lower excited state- rather than the ground state.
It's more efficient to get lasers to do this.
The ground state usually has a very high population- so getting a population inversion is very difficult if the lower state is the ground.

Because the lower state in the CO2 laser is already an excited state, the reverse process- absorption of the laser radiation by the atmosphere- would only happen if the air contained a significant amount of that excited state.
It doesn't.

It's funny how often global warming deniers fail to get the physics right.

If you want to lose this argument in more detail, start another thread.

20

Physics, Astronomy & Cosmology / Re: How can a universe start from nothing?

« on: 26/08/2018 21:30:05 »

m×c² – 2×G×m×M/r = 0  (we have to count the gravitational term twice because each body exerts on the other, I think...)

I disagree. The potential energy is for the system of two particles in this case so you don't need the two.