1

Technology / Re: How can I achieve even heating with induction cooking?

« on: 08/05/2022 22:56:59 »

Of more concern is that the bundle of wires appear to be plastic-insulated.

The wires appear to be standard enamel insulation.  Also, the plastic tie-wraps are not showing any damage so far.

2

The Environment / Re: (What's) the optimal temperature for life?

« on: 01/05/2022 16:11:28 »

in a sterile desert, more life will grow if the temperature falls

No. In a sterile desert more life will grow if there is more water available at the surface. Of course - more water available at the surface will also cause surface temperatures to fall, due to increased evaporative cooling. Temperature is an issue in many hot arid areas - such as the Sahara - due to lack of water. The equator gets more sunlight above it, but also has more clouds, and more water (at the surface) to cool it. So water is the issue in arid areas - not temperature.

BTW: In some arid regions of China day-time, growing season, temperatures fell by over 6C when mass irrigation was introduced. See: Yang/Huang/Tang, 2019

3

Physics, Astronomy & Cosmology / Re: Why don't gamma rays have a higher speed?

« on: 21/02/2022 13:20:51 »

Do any Europeans care about cricket?

Yes.
Notably quite a lot of Europeans who live in England care about Cricket.
Ask a geography teacher for further clarification.
(Don't ask a politician; they don't seem to understand).

4

Physics, Astronomy & Cosmology / Re: Why don't gamma rays have a higher speed?

« on: 20/02/2022 15:35:57 »

Hi again.

....and the idea of a massless particle transferring momentum really does confuse people.

     I'm definitely with you, or at least sympathetic to, a lot of what you've said alancalverd.    It connects with something I was trying to get together and tidy up to make a post.   I'm just going to post it now, scruffy as it is...

    I would like to target something that @evan_au  mentioned first but lots of other people have also added to.

Massless particles (eg photons or the hypothetical graviton) which carry energy can only travel at "c"
(ES adjusted the spelling of the word "the")

    Go for it, evan_au, or anyone else reading this.  Present your proof or provide links to a reference etc.   

I've seen a lot of partial proofs and plausibility arguments but nothing that I'm completely happy with.   It doesn't mean it's wrong, I don't know everything - I'm just old enough and stubborn enough to question every little detail these days.

    A lot of arguments will start from this equation   

E²  =  m²c⁴ + p²c²       

[Eqn.1]

(with the usual meanings,   p = 3-momentum,  m = rest mass   etc.)

    ....because I would stop you there and ask exactly how you derived that equation to start with.    For massive particles that equation is easily obtained by considering the 4-momentum, P^μ, of a particle.    It's simple enough since a 4-velocity, U^μ = is well defined for particles with timelike paths and then we can define P^μ = m U^μ.   

      However, for particles that follow null paths we can't use the same tricks:  The 4-velocity is not defined since =  0   on a null path.   It seems common to just introduce a new definition for the 4-momentum of a photon,

P^μ  =   ( E/c   ,   V_xE/c² ,  V_yE/c² ,  V_zE/c² )      with  V_x = x-component of velocity (w.r.t. co-ordinate time) for the photon etc.
   ... but the question is how did you come to decide on putting those particular components into the 4-momentum? 

   The only "proof" or plasuibility argument I've ever seen for that definition of the 4-momentum of a photon is based on using some additional infomation about the behaviour of photons.  Something that you could observe in experiments on photons but is not otherwise obviously true for all massless particles.
    For example, assuming straight away that the momentum and energy are related  by  p = E/c.   Alternatively, you can derive that form for the 4-momentum under the assumption that the 3-momentum  in any spatial direction will be proportional to the velocity (w.r.t. co-ordinate time t and not proper time Tau) of the particle in that direction.   Another "proof" I've seen utilises a 4-wave vector for the photon (which assumed the photon had wave-like properties and propagated at speed c to begin with).   Anyway, all of these things are extra pieces of information you could obtain by experiment on light but I don't see why they're necessarily true for arbitary massless particles.

Best Wishes.

LATE EDITING:   This article,  https://www.wtamu.edu/~cbaird/sq/2014/04/01/light-has-no-mass-so-it-also-has-no-energy-according-to-einstein-but-how-can-sunlight-warm-the-earth-without-energy/
is quite a good one, it's easily readable by non-specialists, if anyone wants a general guide for why massless particles travel at the speed c.   It's typical of many Popular Science articles where E² = m²c⁴ + p²c²  [Eqn 1]  is the basis or starting point for the  argument.

5

Physiology & Medicine / Re: Can we combine axolotl DNA with human DNA?

« on: 10/02/2022 05:17:57 »

So until there are some major breakthroughs, I suggest that researching limb growth is perhaps a thousand to a million times harder than producing a vaccine against one variant of COVID.

If we think linearly, the obstacles are seemingly impossible to overcome. But technological progress is exponential. If the effectiveness of our technology improve by twice a year, we will get a million fold improvement in just 2 decades.

6

Physics, Astronomy & Cosmology / Re: Would string theory enable very long distance communication?

« on: 07/02/2022 17:46:06 »

I guess it's just me...
https://en.wikipedia.org/wiki/Tin_can_telephone

7

Physics, Astronomy & Cosmology / Re: What would your reaction be to a sudden volcanic eruption burst on the moon?

« on: 17/01/2022 19:30:44 »

What would the scientific community's reaction be to a sudden volcanic eruption from a moonquake(s)?

For about the first second, nothing at all.

8

Just Chat! / Re: Should we relegalize dueling?

« on: 07/10/2021 19:40:40 »

In countries with a public health system (eg not the USA), the health system consumes a large fraction of the taxation income.
- Dueling will only increase load on the health system, since it your taxes that pay to patch up the people who partially survive the dual.
- If there is no real public health system (eg the USA), gun violence is rife, and people are encouraged to get more guns to protect themselves from the idiots with guns. There is no incentive for the government to do much about it, because repairing the damage doesn't really come out of their pockets.

It was ironic to hear Donald Trump criticizing the mayor of London on a night when 3 people were killed in stabbings, when the homicide rate in New York was twice as high (you are much more likely to die from a gun attack than a knife attack).
See: https://www.bbc.com/news/uk-england-london-48651131

There is a branch of mathematics called Galois Theory, applied in 4G mobile phones and cable TV, among many others. Galois documented this in a letter at age 20. He had foolishly challenged a soldier to a duel, and died of gunshot wounds received the next morning.
See: https://en.wikipedia.org/wiki/%C3%89variste_Galois

The relevant difference between the US and the UK is that neither of them allow duelling.

9

Physics, Astronomy & Cosmology / Re: Why do objects travel through space-time and not space and time?

« on: 23/08/2021 03:07:44 »

The twin paradox comes about because the "stay at home" twin has a constant time coordinate

Actually, he has a constant spatial coordinate (at least in the Earth frame) and the time coordinate is the only one that varies (by a year).

and so has a "shorter" worldline through spacetime than the "leave home" twin

E-S has the gist of it. Minkowskian spacetime isn't Euclidean. In Euclidean spacetime, 4D distances would be computed as √(t²+x²+y²+z²) but spacetime intervals subtract the xyz from the time: s² = t²-(x²+y²+z²). So the straight line (Earth result in the longest interval, and the shortest interval (that followed by light) is where t² equals distance². So I'd say the travelling twin has the shorter worldline, as measured as an interval.
A spacelike worldline (where spatial separation is greater than temporal separation) results in a negative interval s², meaning s would be imaginary. Nothing can 'follow' such a worldline.

10

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

« on: 30/06/2021 00:15:29 »

I think the question relates to shielding materials used during radiographic weld and pipe integrity inspection.  Personnel shielding around the pipe is most likely to be lead, usually sandwiched in plastic or plywood, but the radiation source  is often a radionuclide pellet that is carried in a "torch" with tungsten or uranium filling.

Depleted uranium isn't much less radioactive than the natural stuff, which contains less than 1% of U235, so most of the U235 emission is actually absorbed by the bulk U238. The problem is its reactivity and alpha emission - it can deliver very large doses to e.g.lung tissue if the dust is inhaled.

11

General Science / Re: How does one Quantify the Colors of a Quark?

« on: 14/06/2021 13:58:21 »

I don't have a direct link to the story behind why they named it 'colors'.

But           " As mentioned and shown in Figure 1, quarks carry another quantum number, which we call color. Of course, it is not the color we sense with visible light, but its properties are analogous to those of three primary and three secondary colors. Specifically, a quark can have one of three color values we call red (R), green (G), and blue (B) in analogy to those primary visible colors. Antiquarks have three values we call antired or cyan (¯R), antigreen or magenta (¯G), and antiblue or yellow (¯B) in analogy to those secondary visible colors. The reason for these names is that when certain visual colors are combined, the eye sees white.

The analogy of the colors combining to white is used to explain why baryons are made of three quarks, why mesons are a quark and an antiquark, and why we cannot isolate a single quark. The force between the quarks is such that their combined colors produce white. This is illustrated in Figure 5. A baryon must have one of each primary color or RGB, which produces white. A meson must have a primary color and its anticolor, also producing white. "

https://courses.lumenlearning.com/physics/chapter/33-5-quarks-is-that-all-there-is/

Does it pretty well.  I used to have a more 'original' and rather fun link to how they came up with it but it's unfortunately gone.

12

Geek Speak / Re: Why the median does not change?

« on: 14/06/2021 11:54:22 »

A common example where the median is preferred over the mean is wealth, because the mean gets distorted by a tiny number of mega-rich people.

13

Physics, Astronomy & Cosmology / Re: what would happen if gravitational mass were different than inertial mass?

« on: 12/05/2021 07:13:30 »

just like the rotation of the planets in the Solar System prevented the Solar System from collapsing into the Sun.

The correct term is revolution of planets, instead of rotation.

14

Physics, Astronomy & Cosmology / Re: Why Didn't Einstein FULLY Address Simultaneity-at-a-Distance?

« on: 25/04/2021 15:53:05 »

This Veritassium video suggests that Einstein did address simultaneity at a distance, by saying it is impossible to measure, and defining the convention that the speed of light is identical in every direction.
[...]

At about the 15 minute point in the video, the author says that it's possible that in some directions, we're seeing extremely distant galaxies as they were in the distant past, whereas in other directions we're seeing extremely distant galaxies as they are now.  It seems to me that that possibility can be discounted because of the fact that what we see in all directions is amazingly uniform, and that seems to contradict our understanding that the universe has greatly changed since the big bang.

15

Physics, Astronomy & Cosmology / Re: Can you measure the one way speed of light without synchronised clocks?

« on: 25/04/2021 01:30:39 »

FWIW Veritasium has a video about this exact topic:

16

New Theories / Re: Magma vortex hypothesis about earthquakes.

« on: 22/04/2021 20:59:31 »

The hypothesis presented can be easily tested if a firecracker is blown up under the ice.

17

COVID-19 / Re: Should we have tried the inactivated virus approach to vaccines for Covid-19?

« on: 14/04/2021 09:39:43 »

Sinovac's coronavac looks like it's about on par with other vaccines. Perhaps not quite as good but given a bad press

18

Physics, Astronomy & Cosmology / Re: How do galactic jets form?

« on: 11/04/2021 22:41:28 »

Here is the link.
https://eps.leeds.ac.uk/maths-astrophysical-geophysical-fluid-dynamics/doc/relativistic-astrophysics

19

Physiology & Medicine / Re: Can measles erase the body's antibody memory?

« on: 21/03/2021 17:49:25 »

Yeah, measles creates immune amnesia. It came to light because when measles jabs were given in the third world, childhood mortality went down massively, lagging by about two years- whereas the measles vaccine acted almost immediately. Turned out, having had measles in the last two years left the immune system as a smoking ruin that took a while to get working again, and that leaves people susceptible to getting diseases that can kill them.

Allowing for that effect, it turns out that measles was indirectly killing up to 1% of the people it infected- making it even worse a disease than people thought it was.

20

Physiology & Medicine / Re: Can measles erase the body's antibody memory?

« on: 21/03/2021 10:59:04 »

(and I find it unlikely that measles would erase other antibody responses)

I also thought it unlikely but...

https://science.sciencemag.org/content/366/6465/599