1

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.

2

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.

3

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.

4

Physiology & Medicine / Re: Honey against sugar: which sweetener should I use?

« on: 25/08/2018 11:08:21 »

Oh, I forgot to mention the only case where it's likely to matter
"Honey is a known dietary reservoir of C. botulinum spores and has been linked to infant botulism. For this reason honey is not recommended for infants less than one year of age"
from
https://en.wikipedia.org/wiki/Botulism#Infant_botulism

5

New Theories / Re: Who is the author of the theory of tidal resonance?

« on: 17/08/2018 20:40:18 »

Yusup. Instead of spewing out new questions on this, go and open it up in New Theories.
It's very clear that you're not satisfied with peoples answers, that means that you already have a opinion.
Place that one in New Theories.

Or be banned
Because that is what I would do if I was a moderator here.

Looking at this sub forum it seems you fill it up Yusup, asking the same questions in various disguise,
That's not how the TNS is thought to work.

6

General Science / Re: Is drinking water better off alkaline?

« on: 11/08/2018 00:58:32 »

water is more natural so it is better

Would you like to show how you can parse that  statement in a way that makes it helpful?

7

Physics, Astronomy & Cosmology / Re: Does hot air gain potential energy when it rises?

« on: 04/08/2018 20:53:35 »

Temperature is a form of kinetic energy (largely), and therefore we would expect a mass of warm air to cool as it rises, as the kinetic energy of its temperature gets exchanged for potential energy of its height (and this is typically what is observed).

Excellent response. My compliments to the chef!

8

Physiology & Medicine / Re: What's the best way to hydrate?

« on: 06/07/2018 15:50:20 »

I am eager to be shown wrong,

Happy to help
https://www.nhs.uk/news/food-and-diet/a-small-amount-of-coffee-will-not-dehydrate-you/

9

That CAN'T be true! / Re: Are LEDs harmful to health?

« on: 27/06/2018 22:58:27 »

bluer frequencies ...can interfere with our sleep-wake cycle.

The idea that some cell in the eye was affecting sleep/wake cycles (the circadian rhythm) was supported by certain blind people who stayed synchronised to the day/night cycle, despite having no rod or cone cells in their eyes.
It was eventually traced to a special type of cell in the retina, which is sensitive to the blue light of day, but provides no perceptible conscious input.

So, to be safe, use the "warm" types of LED in the bedroom, or areas where you relax before going to bed.
See: https://en.wikipedia.org/wiki/Intrinsically_photosensitive_retinal_ganglion_cells#Research_in_humans

10

Physics, Astronomy & Cosmology / Re: What are the pressure differences within sound waves?

« on: 12/06/2018 17:47:13 »

The sound pressure of 100dB is not an absolute measure against local air pressure, but a measure against a reference auditory threshold of 2x10^-5 Pa.
So to find the actual pressure you would need to use:



Where p₀=2x10^-5 Pa
L_p=100

P is rms pressure and it is pressure swing either side of ambient - there are compressions & rarefactions so pressure difference between these two is 2p.

In a free field - no reflections - p decreases at 6dB for every doubling of distance so p varies as 1/r not 1/r².

The air molecules vibrate rather than move so there is no net movement of air.

11

Physics, Astronomy & Cosmology / Re: If nothing is faster than light, how can we look back in time with a telescope?

« on: 24/05/2018 12:39:03 »

If nothing is faster than light, how can we look back in time with a telescope?

An example: Chinese observers saw a "guest star" in the sky in the year 1054.
- It was bright enough to see in the daytime.
- We now know that this was caused by a supernova about 6,500 light years away.
- The expanding fragments are now known as the Crab Nebula.
- The supernova actually took place around 5,500BC (roughly 1054 minus 6500 years).
- So when the astronomers saw it in 1054 AD, they were looking back in time about 6500 years.

But supernovae also emit some other particles that travel at well below the speed of light. This probably includes radioactive iron nuclei, ⁶⁰Fe.
- If these are traveling at (say) 2/3 the speed of light, they will take about 10,000 years to arrive at Earth (compared to 6,500 years for light)
- We can expect these to start arriving around the year 4,500 AD.
- So assuming that scientists then have radiation detectors in space, they would see this increase in subatomic particles.
- They would be effectively looking backwards in time at the same event - only now they will be looking back almost 10,000 years
- We can see a sprinkling of ⁶⁰Fe on the sea floor, hinting at nearby supernovae in our galaxy. This isotope has a half-life of about 2 million years, so we know that this did not occur naturally on Earth.

So far as we know, there is nothing that travels faster than light, so no high-technology astronomers on Earth could have seen the Crab Nebula explosion before 1054.
- There is one subtle exception: Neutrinos. It is estimated that a supernova in the core of a giant star may take from a few hours to a day to break through the surface of a star, emitting an intense flash of light, X-Rays and gamma rays. However, neutrinos (which travel imperceptibly less than the speed of light) can make the same trip from core to surface in a few seconds. So neutrinos might arrive at the Earth from the core of the supernova a few hours before the flash of light from the surface of a supernova. With today's neutrino detectors and X-Ray/Gamma ray detectors, I expect we would be able to measure this time difference if another supernova exploded to us as close as 6500 LY.

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

edit: Correct formatting of the iron isotope, as highlighted by PmbPhy.

12

Marine Science / Re: How can climate scientists claim 30% acidification of the ocean due to CO2?

« on: 12/05/2018 01:10:07 »

It is the phase relationship between temperature and CO2 that questions the accepted "wisdom" of anthropogenic climate change.

Which is plainly a bit silly.
Whether the CO2 takes a few months to turn up in the sea water isn't the issue here.
The "wisdom" of anthropogenic climate change is based on a number of factors; let us know which you disagree with.

(1) Humans have been burning a lot of fossil fuels in the last hundred years or so.
(2) That generates CO2  which (at least on a scale of centuries) ends up in the atmosphere.
(3) We know this because the excess CO2 in the air  tallies with the  stuff we have added.
(4) The CO2 levels in the air are rising.
(5) The added stuff has an "ancient" carbon dating age- which is consistent with it being from fossil fuel but not with it being from any more recent source.
(6) Additional CO2 in the air  means that more of the Sun's incoming radiation is trapped by the Earth- because that's what physics tells us..
(7) The temperature is rising.

13

Physics, Astronomy & Cosmology / Re: How fundamental is time?

« on: 01/05/2018 18:01:50 »

Interesting thoughts.
Do we have the same problem with distance, there is no true origin. All measurements are Δx, Δy or Δz.
Similarly, units are arbitrary.

14

General Science / Re: Why do wasps sting us?

« on: 23/04/2018 17:35:56 »

The majority of wasp species are solitary and do not sting, it is only the females of social wasps that sting.
Most stings occur in late summer. In the early part of the year social wasps gather protein to feed the brood, eg caterpillars, and are rewarded by a sweet excretion from the lavae. In late summer the brood rearing ends and the sweet substance is no longer available, this is when they go searching for a replacement and get into contact with humans. Most stings are accidental eg inadvertently crushing a wasp, or a  panic flap which triggers an attack at the fast movement. Quite often if you sit still a wasp will land on your hand, clean, and leave. It is also true that they don’t like mammal breath, which they view as a threat, combine this with rapid movement and you will get stung.

Whoops, Chris replied while I was typing

15

Physics, Astronomy & Cosmology / Re: Does quantum entanglement allow instantaneous information transfer?

« on: 12/04/2018 14:10:25 »

As I understand it, quantum entanglement does not involve instantaneous information transfer.

It is very hard to give examples that are both accurate to QM and relatable to our experiences, but the common comparison is this:

Two twin brothers want to share their birthday cake, but they are both on vacation in different places. Their mother cuts the cake with a single slice and sends each piece to one of her sons. Until opening the package, neither son knows whether the cut was made evenly, or if the other twin got a larger or smaller piece. It doesn't matter how far away the twins are, when one opens his package to see 60% of a cake, he instantly knows that his brother will be disappointed.

This example is representative of most QM entanglement sort of experiments in that an operation (cutting of the cake) is done that produces two complimentary things (slices of cake), which are then sent mailed) different ways such that information about them is unknown until the thing is actively inspected (package opened). The example falls short of QM reality because the outcome (who got how much cake) is determined by the mother (and she knows)--and even if some randomization is introduced, it still doesn't quite capture the nature of superposition... but it works well enough.

There is nothing magic about the instantaneity here. Each twin already has the knowledge that the cake slices will together add to one cake, and then presented with one slice, has all the information required to know the size of the other slice. This breaks down if their assumption is invalid (maybe mom ate a piece too). It is also important to remember that it still took time to send the cake to each of the twins, so the information sent from mom to son is constrained by the speed of light. That each son gains insight into both packages at the same time is only a matter of logic, not physics.

This example is classical an of course it makes sense. However, this implies a single hidden variable...quantum mechanics doesn't. That's the difference.
In the classical example, we have slice A and B. The kid can look and it test is wether it is A and make another test to see if it is B. Suppose it is A. The kid makes a test to see if it is B and yields negative. And if it tests fot A gets positive. So the hidden variables are Tested A + / tested B - and for the other pair the opposite signs. So the hidden variable can be a matrix that can have two options  (+,-) or (-,+), which can be represented by 0 or 1, so a single boolean variable, for a classical particle you would need an infinity (in quantum you need none ). That's classical.
Now in quantum the state is not defined until a measurement is done. So it seems an instantaneous action at distance. Even with the detection of a single particle emmited by a source, the particle is everywhere until measured then it disappears from all positions and reveals itself on a single one. In other words a measurement here makes the particle appear here and vanish from all other superpositions. But at least what is clear is that there unlike particle travel as waves, the collapse of a quantum field does not involve waves or signals traveling. I don't get it. I think something is wrong either with relativity or QM, if not with both.

16

Physics, Astronomy & Cosmology / Re: How many different shapes of snowflakes are there?

« on: 03/04/2018 11:56:08 »

There are 30-odd shapes of ice crystals, depending on temperature and humidity.
The shape depends on the precise path the snowflake takes through the cloud, with changing temperature and humidity, with the growing edge changing from one crystal form to another as the crystal grows.
Not all snowflakes have arms, but for those that do: all 6 arms take pretty much the same path through the cloud, so all 6 arms are roughly the same shape.

17

Physics, Astronomy & Cosmology / Re: Can black holes rotate along more than one axis?

« on: 03/04/2018 05:11:36 »

(Just to be sure I am interpreting the smoke-ring bit correctly, JeffryH and Kryptid... If we had a cylinder spinning along its axis (clearly with net angular momentum), and then bent it around into a torus while maintaining the "spinning" motion so that the surface of the torus moves from the inside (facing the donut hole) to the outside (facing out) and back, is that what you are calling "smoke ring like rotation"?)

Yes.

18

Chemistry / Re: Is there an easy (cheap) way to identify aluminium alloys?

« on: 21/02/2018 16:29:35 »

yeah, etchrate information is a good way as well, although I don't know the differences between allows.  I'm in semiconductor and we use a lot of different chemicals for selective etching of customer shields.  A while back I found some valuable etch tables.  I can't post a link, but if you google "kirt williams etch rates for micromachining processing", you'll find his tables from a Berkeley website.  There are two papers, a part 1 and 2.  But they only cover Al used in semiconductor, not a bunch of different alloys.  I always start with those tables, and then add my information to our internal knowledge base. 

And yep...the lab can get pretty expensive, as my manager would tell you.  I'm constantly fighting for money for tests.  haha.

Cheers,
Kevin

19

Technology / Re: Is magnetic accu-battery LD feasible?

« on: 19/02/2018 15:08:57 »

Never stop thinking.

If you want to learn science do listen to the podcasts, and if you have any questions do post again.

20

Physics, Astronomy & Cosmology / Re: Why is air pressure higher underground?

« on: 12/02/2018 22:56:00 »

Excellent answer. I was typing my response when you posted your’s and it didnt seem necessary to add anything. Other than, start clearing your ears as soon as you leave the surface, don’t wait until you are 2.5m down, it will be much harder then.