1

Physics, Astronomy & Cosmology / Re: Acceleration of light?

« on: 25/04/2023 03:38:03 »

Hi.

I completely missed the bit about transitions to different mediums, well spotted @geordief .

Here's a pleasant Physics expert talking about why or how light slows down in glass for a YouTube video produced by Sixty Symbols,  it lasts about 15 minutes  and you might as well listen to him rather than read some waffle I produce.

So here's 4 different answers, which are are more or less bullet points summarising that video as I saw it:

 1.   Light can travel more slowly in different mediums but photons don't.   Don't ask, live with it. 
Be aware that many of the old and popular explanations are wrong.

 2.   A photon is a particle that is only readily identified in a vaccum.   Inside a dense medium which is some regular lattice structure of atoms, what you will actually have is a different particle (sometimes called a quasiparticle) which is known as a "polariton".   These polaritons travel at less than the speed of light.
     So the photon wasn't accelerated or ever travelling at less than the speed c,   instead it was just changed into a polariton once inside the dense medium.

  3.  The photon is a quantum mechanical object.   It can take all possible paths through the medium and some of those involve an interaction with other QM objects like electrons and nucleons that are present in the dense medium.  The sum of all the possible paths is such that the overall wave description looks like a photon that has been delayed (travelling at less than c).
     There are similarities between the Quantum Mechanical model and the explanation using classical electromagnetic waves.  With the classical model, an e-m wave passing close to an atom will cause charged particles like the electrons of the atom to oscillate.  However, oscillating electrons will produce their own electromagnetic waves.   So these will interfere with the main wave that was passing through.   (For the QM model, we have that one photon takes mutiple paths so it is all the wave you need on its own and also the interactions with electrons are "like" the classical interaction in some broad sense).

4.   I'm not actually certain I can really articulate a 4th answer.   I'm just fairly sure you could find one if you tried.

Best Wishes.

2

General Science / Re: Why does supercooled water stay liquid?

« on: 21/11/2022 21:20:13 »

It's said that a picture is worth a thousand words. I think a video is worth even more.

At least there are 2 interesting facts shown here:

Nucleation can start from a place seemingly lack of contamination.

Density of supercooled water doesn't seem to change when it freezes.

3

General Science / Re: Why is gold gold?

« on: 19/11/2022 19:55:47 »

The thing that flags on gold is the photo electric effect with it able to absorb blue end light

The photoelectric Work Function of Gold (5.1eV) is not that much different from Aluminium (4.08eV)
- But they are in the "wrong" order for this hypothesis - if gold absorbed blue light by the photoelectric effect, then Aluminium should do it even more strongly.
See: http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/photoelec.html

For visible light, the range of photon energies is 1.63eV (red) to 3.26 eV (violet), which is less than the work function of gold or aluminium, so no electrons will be ejected. That is why the photoelectric effect is measured with UV light.
- Interestingly, Calcium, with a work function of 2.9 eV would see a photoelectric effect with visible light at the violet end of the spectrum
- But we usually observe Calcium in oil (no photoelectric effect) or air (coated with an oxide).
- Measurements of the photoelectric effect have to be conducted on bare metal, in a vacuum.

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Physics, Astronomy & Cosmology / Re: Negative Space?

« on: 22/10/2022 13:55:16 »

Non space should be whatever space is expanding from.

Or into?

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Physiology & Medicine / Re: Spammy meds- Enjoy Awesome Sex With Your Sex Life Partner!

« on: 13/08/2022 12:17:10 »

I am experimenting with corned beef and tuna. At least, that's my excuse.

Is that the new surf & turf?
Are you planning a recipe book or website?

6

Just Chat! / Re: What is on your bucket list?

« on: 31/07/2022 08:35:15 »

I'd like to see a tornado before I die …….

The proximity of those 2 events might depend on how close you are 

7

Technology / Re: Are solar panels worthwhile?

« on: 18/04/2022 10:52:29 »

Depends on what you use to generate the power. Coal is cheap, and common in China, where 90% plus of all solar panels are made, though hydropower is also a good part of the energy mix there, so the energy mix is somewhat different. The advantage of solar is that they can last 25 years plus, and thus will recoup the energy in production, and are also recyclable with relatively little extra effort, as now you have the components easy to separate, if somewhat labour intensive, but still worth the energy 25 to 50 years down the line.

8

Plant Sciences, Zoology & Evolution / Re: How does natural selection work?

« on: 18/03/2022 21:25:35 »

Hi.

    The main details for natural selection have already been presented.    Most DNA alterations are just random mutations  etc.

    I haven't studied Biology for years but this was one of the more "funky" or convention-defying contemporary ideas that was discussed back in the day.   It's useful to suggest that your DNA doesn't always dictate what you do, sometimes it can be the other way round....

    There's a small chance that DNA transcription to produce proteins isn't always a one-way process.   There are viruses with RNA reverse transcriptase enzymes so that RNA can be converted to DNA.   This opens the door to the possibility that information may sometimes flow in that direction from RNA to DNA which might then get incorporated into the nuclear DNA of the cell.
     Lets take a simple model:   A host organism has a physically demanding environment in which it must survive and to do this it is using a lot of muscle and this exercise is building more muscle in the usual way.   This means there is a lot of RNA in the cytoplasm that encodes for muscle proteins.   If a virus gets on board, some of that RNA can be reverse transcripted into DNA which could end up getting incorporated into the nuclear DNA stores.  The host organism now has two (or more) copies of the gene encoding for the muscle protein, so they are likely to get a higher transcription rate of RNA encoding for that protein from then onward.  This means there has been a permanent change in the amount of muscle protein the organism will synthesize - but, more importantly, if that change has occurred in the germ cells of the organism then this change is passed on to future generations.
    The effect is minor, if it happens at all, but it's interesting.   It's the possibility that the actions of the organism during its life might influence the DNA.   The whole set of circumstances falling into place, like accidental incorporation into the nuclear DNA, would only be a one-in-a-million chance but that is precisely the sort of scale we're talking about for evolution over many years.  It probably isn't going to be the main route for evolution but it could be a boost to the process.

Best Wishes.

9

Physics, Astronomy & Cosmology / Re: How did this rocket stage gain the energy to get to the moon?

« on: 07/03/2022 20:34:49 »

A rocket that is launching a probe to the Moon needs to put the probe (and itself) into an orbit which has an apogee (farthest distance from the Earth) that is around 370,000km (the Moon's average distance from the Earth). But you don't want to aim for the visible center of the Moon (or your rover will crash at high speed, and not rove very far). You want to miss the Moon slightly, so the probe can enter Lunar orbit (by the smaller probe firing it's smaller rockets).

Now the booster is in a very elliptical orbit that has an apogee (farthest distance from Earth) of around 370,000km, and a perigee (closest distance from Earth) that is in Low Earth Orbit, perhaps a few hundred km, and an orbital period of a few weeks. If the operators are responsible, they will give the booster another boost when it is out near the Moon to (1) use up all the fuel in the tanks, so it doesn't explode and spread shrapnel into low earth orbit and (2) increase the perigee so that it doesn't come zipping past the ISS and other valuable satellites every 2 weeks.

So you now have a rocket booster in a very elliptical orbit around the Earth  every few weeks, reaching out as far as the Moon; and the actual Moon passing through the path of that orbit about every 4 weeks. Sooner or later, their paths are likely to cross, and in that encounter, the Moon comes off in better shape than the rocket.

Before there is an actual crash, there will probably be several near-misses (including the first, intentional near-miss), and some of the Moon's momentum is transferred to or from the rocket body; the Sun's gravity and solar wind also push around the booster (which is now basically a large, empty, aluminium can). That puts the booster in a somewhat chaotic orbit, making it harder to trace back the orbit to its origin, or to pinpoint many years into the future exactly when it will crash into the Moon.

Oops! overlap with Halc...

10

The Environment / Re: Is hydrogen a better fuel source for the environment?

« on: 15/02/2022 23:20:24 »

That is 3 times the drag for the same distance at 3 times the speed, that is very convenient.

No, it is 9 times the drag force, over the same distance. Energy = force x distance.

11

General Science / Re: Why did our brains evolve to perceive 12 musical notes?

« on: 30/01/2022 20:51:52 »

Our modern Western instruments are "even-tempered", with the frequency of adjacent notes differing by the 12th root of 2 = ¹²√2.
"Counting up 12 notes" = "Raise ¹²√2 to the 12th power", and you end up with a frequency ratio of 2, or one octave.
- With this tuning, you can play a musical piece written for any (Western) key.

But Pythagoras and friends (who developed the basis of Western harmony) would have objected to this tuning, as it does not produce exact small-integer ratios between the frequencies. They would have described the tuning as "off".
- Before the "even-tempered" tuning was accepted, "Concerto in D Major" had to be played on an instrument tuned for that key.
- Some people prefer "perfect tuned" instruments, and some electronic instruments even let you switch between even-tempered and perfect-tuned (in various keys).

...or you could follow Alan's advice, don't fret about it, and just play a violin.

12

COVID-19 / Re: Do heavy colds help prevent covid infection?

« on: 13/01/2022 20:18:46 »

The classic "cold/flu symptoms" are actually a side-effect of Interferon, a signaling molecule produced by your body when it detects a viral attack.
- Interferon activates the immune system
- Interferon also slows down some normal cellular functions, so the virus can't hijack them

A unique "stealthy" feature of COVID is that it suppresses production of interferon by infected cells, so that it can spread "under the radar", infecting not only you, but those around you before symptoms appear.
- It makes sense that if your Interferon levels are already high due to the common cold, an incoming COVID virion would have a harder time gaining a foothold in your body

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

13

Physiology & Medicine / Re: Immortality

« on: 13/01/2022 08:15:25 »

One of the problems with immortality is entropy: We can't beat it.

One novel solution I heard is this (at least for people living in The Matrix):
- Computing is very efficient on quantum computers (at least in theory)
- But quantum computers need to be very cold, and that takes lots of energy when the world around us has a temperature well above absolute zero. (Running a refrigerator increases entropy)
- One idea is to locate your quantum computer in deep space, where the ambient temperature is 2.7 degrees above absolute  zero; so you have much less energy wasted in your refrigerator
- For those thinking on a much longer timescale, if you wait for the temperature of the universe to drop to less than 0.001 degrees above absolute zero, you probably won't need a refrigerator at all!
 

14

Physics, Astronomy & Cosmology / Re: Is clockwise the predominant direction for solar systems and galaxies ?

« on: 11/08/2021 16:44:42 »

But does the rotation of the galaxy have an effect on the rotation of the solar system? Are we side on, are we  coplaner with the galaxy and rotating backwards?

Not particularly, no.

The plane of the galaxy (yellow) meets the plane of the solar system (red) at an angle of just over 60 degrees.
Here a diagram of both, with the celestial plane (the blue plane passing through our equator) also included.

15

Physics, Astronomy & Cosmology / Re: Can you handle old pipe X-ray radiation shielding?

« on: 30/06/2021 10:38:09 »

Nomenclature. It certainly becomes "irradiated" but not "activated".

And the lead coats are not always a Good Thing. Two of Her Majesty's Specialist Inspectors required a client of mine to  wear a lead coat when handling very high energy gamma emitters. This (a) slowed him down so his exposure was extended and (b) increased his skin dose through secondary emission. Thin lead sheets are actually used in industrial radiography as "intensifying" screens to convert a few incoming high energy photons to large numbers of low energy photons and electrons that are absorbed by the x-ray film (or operator's skin).

Not a game for amateurs. But the lead itself is fairly innocuous if undamaged.

16

Physics, Astronomy & Cosmology / Re: Could the core of a body have repulsive gravity?

« on: 27/05/2021 21:43:35 »

Any 'body' has mass, and mass is correlated with positive gravity, meaning that if you took the core of the body away and replaced it with a hollow ball of much less mass that is strong enough to take the pressure, the body in question (sun say) would have less gravity. Hence the core adds to the gravity, and contributes positively.

There is such a thing as negative mass density, and it very much does repel.
Imagine an infinite grid of objects of equal mass at regular distribution. Each will just sit there, being balanced in all directions by gravity from all the objects distributed evenly around it. Now consider the same arrangement but with one of the objects missing. This creates said negative mass, resulting in a chain reaction starting with the immediate neighbors of this 'hole'.  All the objects will, by negative gravity, be repelled by this low density region, making the region bigger and accelerating the effect.

Look up the dipole repeller for an example of exactly this, a region of negative gravity expelling all nearby galaxies in all directions. This was apparently only discovered 4 years ago. There's also the cold spot repeller, even larger and further away.

17

The Environment / Re: Can we use the energy underground to replace fossil fuels?

« on: 26/03/2021 20:48:01 »

the imminent development of cheap simple fusion plants makes it even less likely that it will ever come to pass.

Could you give further information, please,  about the imminent development of these "fusion plants"?

They would be so exciting, and would solve all our energy problems! 

Alas, I don't think you will reply.

18

General Science / Re: SPAM TUB SPECIAL - The Washing Machine SPAM Service Center

« on: 17/03/2021 23:42:27 »

So my washing machine caught fire today
The good news is I was able to get my washing and drying done all in one go.

19

Just Chat! / Re: Member type

« on: 22/02/2021 07:28:59 »

I think if you have any questions about Chris’s member they would be best sent in a pm. He doesn’t expose details to us despite his nakedness! 

20

Just Chat! / Re: What exactly is a "full English breakfast"?

« on: 10/02/2021 00:13:20 »

One memorable morning in the last century I had breakfast in St Bartholomew's Hospital staff restaurant, with an American x-ray sales rep.

Leathery eggs swimming in grease, bacon cut from the uppers of an army boot, 20mm black armor-piercing sausages, postmortem hypostatic tomatoes, cold rubber toast with frozen butter, and lukewarm bilge in a coffee cup.

At the checkout my colleague asked "How can you f**k up an English breakfast?"

"800 years of practice, sir" was the smiling reply.

What's his face from eastenders tell a simpler joke.

Guy asks for an English breakfast but says I would like you to cook it my way. "Hows that"? the chef replies.

"I want the beans cold on top, tepid in the middle but burnt on the bottom, I want the egg to be the same, I want the fried bread so fully of oil it leaks all over the plate and covers everything in grease, I want the sausages black and hard so when you try and get them with the fork they spring off the plate"

"I dont have time to do all that" replies the chef.

"You found time yesterday!" Replies the guy