1

Physics, Astronomy & Cosmology / Re: What has been learned about Venus from its recent transit?

« on: Yesterday at 12:04:55 »

Recently a twice in a lifetime opportunity occurred

If we were orbiting a star 100LY away, which was on the plane of Venus' orbit, it would not be a "twice in a lifetime" opportunity, it would be an opportunity which repeats every 7 months.

What makes it so rare on Earth is that there is a narrow band where the plane of Earth's orbit crosses the plane of Venus' orbit, and it is rare that both Venus and Earth are in that narrow band on the same day.

if the transits had been across a star say 100 LY away how much would we have learnt ?

If we had a telescope, it had better be above any CO₂ or N₂ in the atmosphere, otherwise we would miss 96% and 4% of Venus' atmospheric composition, respectively. A satellite observatory is strongly recommended!

The amount of light blocked by Venus is (0.95/109)², or 0.0076% of the Sun's area. With a decent model of the age, structure and diameter of the Sun, this would give you an estimate of the diameter of Venus.
 
Of the light blocked by Venus, a tiny sliver of a percentage would have been modified by passing through the atmosphere of Venus. It would be very hard to detect this change in spectrum, even if your space telescope had a very large diameter.

It may be better to take measurements about 4, 5 and 6 months after the transit, where a considerable amount of the light falling on Venus would be reflected in our direction as the illumination of Venus changed from crescent to almost full. Venus reflects about 70% of the light falling on it, which gives a much better chance of working out its atmospheric composition from the subtle changes in spectrum (compared to the transit).

Unfortunately, these spectrum readings would be muddied by the reflection from Jupiter: Jupiter has 136 times the visible area of Venus, but only 1.8% of the light intensity, and half the albedo, producing a similar brightness to Venus.

But the most successful approach may be to use a coronagraph, which blocks out the light from the star, allowing imaging of multiple orbiting planets at once. Unfortunately, an effective space-based coronagraph would require two satellites in orbit, maintaining a precisely fixed orbital relationship relative to the distant star for a long exposure - a very difficult problem in orbital mechanics! A coronagraph has the advantage that it does not rely on the observer having a particular orbital alignment with the planetary system.

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

2

Chemistry / Re: How does a non-polar solvent dissolve a non-polar solute?

« on: 22/04/2018 05:39:27 »

Solid paraffin consists of long hydrocarbon chains that get easily tangled around each other, so the weak intermolecular bonds are enough to make it go solid at quite a high temperature.

In contrast, a small-molecule organic liquid consists of many small molecules that are too small to get easily tangled with each other, so they are liquid at room temperature. In fact, ethane and methane are gases at room temperature, so adding some hydrogen bonding (eg ethanol) or a big chlorine molecule (eg dichloromethane) keeps them liquid at room temperature, and easier to handle. More importantly, there is a much greater density of molecules in a liquid., and this makes it easier to overcome the molecular attraction between the paraffin molecules.

The small organic molecules will have a similar affinity to the long-chain molecules as the paraffin molecules have to each other, so they will become more mobile. When a long-chain hydrocarbon is completely surrounded by short-chain hydrocarbons, it can no longer get tangled with others, and it will be a liquid at temperatures where the pure paraffin would be solid.

3

Chemistry / Re: Does 1 volume of hydrogen + 1 volume of oxygen make 2 volumes of water vapour?

« on: 20/04/2018 11:41:04 »

The question talks about "volumes" of a gas, eg liters, cubic meters or footballs.
- They don't need to specify how much volume is present because gases combine in certain ratios of volume, and as long as the temperature and pressure is the same when you take the measurements, you will get the same ratios.
- This rule of ratios was discovered before scientists discovered the nature of atoms and molecules
- But chemists like to talk about a particular volume called a molar volume of a gas, because you can tell how much mass is present by just looking at a periodic table.
- A molar volume occupies 22.4 liters at 25C and normal atmospheric pressure, independent of what type of gas is present, and has the same number of molecules = 6.022 × 10²³ (Avogadros's constant, abbreviated N_A).
See: https://en.wikipedia.org/wiki/Molar_volume
https://en.wikipedia.org/wiki/Avogadro_constant

So a "mole" of oxygen will occupy 22.4 liters (at 25C) and contains 6.022 × 10²³ molecules of O₂. If you look at a periodic table, you will see that the atomic mass is 16 (or 15.9994 if you want to be really precise). This mole of oxygen will have a mass of 2x 15.9994 = 31.988 grams.
- And a mole of hydrogen will occupy 22.4 liters (at 25C) and contains 6.022 × 10²³ molecules of H₂. If you look at a periodic table, you will see that the atomic mass is 1 (or 1.00794 if you want to be really pedantic). This mole of hydrogen will have a mass of 2x 1.00794= 2.01588 grams.

Now, to address your questions:

1. How many hydrogen molecules are in 2 volume of hydrogen?
2. How many oxygen molecules are in 1 volume of oxygen?
3. How many water vapor molecules are in 2 volumes of water vapor?
please explain. I am confused.

Since we don't know (and don't really care) how big this "volume" is, we can't say how many hydrogen and oxygen molecules are present. But we can say:
- There is the same number of molecules in 1 volume of hydrogen as there is in 1 volume of oxygen
- There are twice as many molecules in 2 volumes as there are in 1 volume
- Assuming that they are all gases, and all measured at the same temperature and pressure

''1 volume of hydrogen + 1 volume of oxygen = 2 volumes of water vapor''

I'm afraid that this doesn't quite stack up.

Now that we do know about atoms and molecules, we can write an equation like:
2H₂ + O₂ → 2H₂O
Which can be read as ''2 volumes of hydrogen + 1 volume of oxygen = 2 volumes of water vapor''.

This is a little tricky, because:
- If you conduct this reaction, it releases a lot of heat, and the temperature is far higher than 25C. So rather than causing a net reduction in volume, it causes a massive increase in volume, quite possibly causing glass to shatter and injuring the person conducting the experiment.
- You will know that at a temperature of 25C, water is not a gas, but is a liquid. So if you collect the hot gases and cool them down, it turns into a liquid which takes up far less space than 2 volumes of gas.
- This is why they have to specify water vapor. But to measure the volume of water vapor at 25C you have to do tricks like measure the volume at increased temperature and/or reduced pressure, and extrapolate to 25C and atmospheric pressure.

Warning: Do not try this experiment at home until you have done it safely, when supervised in a science class. And do wear safety goggles!

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Just Chat! / Re: Puzzles From A Trampolining Upside Down Sheeps Bottom (PFATSB) :-)

« on: 18/04/2018 21:49:08 »

x^6 - 531 x^5 + 117475 x^4 - 13859985 x^3 + 919750924 x^2 - 32549480844 x + 479926006560=0

Can't you fit 5 arbitrary numbers to a 5th degree polynomial?
...although it's tougher if you insist that the unknown 6th number must be an integer
...and even tougher if you insist that all coefficients must also be integers!

5

New Theories / Re: Is it possible to quantize gravity?

« on: 13/04/2018 00:07:13 »

The string theorists already have a good theory of the graviton, which reproduces all aspects of gravitation in General Relativity in weak gravitational fields (eg in our Solar System and most of our galaxy).

What it lacks is:
- Predictive power: The String Theory version of quantum gravity falls down in the same places as General Relativity: near the event horizon of a black hole (strong gravitational fields).
- Uncontrollable infinities. Today's process of Renormalisation does not seem to work for gravity
- Evidence of extra 6 or so dimensions: This is the theoretical basis of today's string theory, but there is no observational evidence to support it

So if your theory can predict what happens at the event horizon of a black hole (and control the infinities), you may have an advantage over General Relativity and String Theory.

Fortunately, the "Black Hole Telescope" should become operational in the next year or so - able to image the black hole at the center of our galaxy.
Unfortunately, you will need to examine a black hole fairly closely to see if your prediction is correct, and this radio telescope will just give us a general outline of the black hole...

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

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Physics, Astronomy & Cosmology / Re: Why do objects move inertially according to Newton's laws?

« on: 09/04/2018 12:09:28 »

The increase in inertial mass

Ah... I see now that Jeffrey was talking about relativistic conditions, where inertial mass is not a constant.

But under relativistic conditions, an object no longer obeys Newton's laws
- or you have to bend F=ma to say that m varies with velocity or gravitational potential - and that the time you use to measure acceleration also changes.
- these are not modifications that Newton would recognize!

7

Physics, Astronomy & Cosmology / Re: What causes lightning jets, sprites and elves above thunderstorms?

« on: 07/04/2018 09:04:16 »

It was once thought that lightning only occurred from cloud to ground, or cloud-to-cloud.

But the ionosphere is a conductive layer well above the clouds, and this could take part in electrical discharges.
- Because the air is thinner up there, it doesn't form a bright lightning bolt like we see for ground strikes.
- The path between collisions with air molecules is greater, so charged particles and ions can reach far greater energy than in familiar lightning bolts - enough to create X-Rays.
- It may be able to smash atomic nuclei together hard enough to produce gamma rays, but this is a little more mysterious.
- The Earth's atmosphere is continually being bombarded by charged particles from the Sun, and this might lead to some charge imbalance between the ionosphere and ground. Some of these events create a temporary electrical path between ionosphere and ground.

See: https://en.wikipedia.org/wiki/Upper-atmospheric_lightning

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Just Chat! / Re: pmb is mentally ill

« on: 06/04/2018 12:32:01 »

I know someone with bipolar disorder. She was a consistent achiever when she was on medication, but when she stopped the medication, she became quite unpredictable.

I had heard that lithium can cause kidney problems. tk's link to NIH actually put an upper limit on the blood serum concentration of lithium.

I've heard it suggested that some of the traditional destinations to take in mineral waters had naturally high concentrations of lithium. It may have stabilised mood in the people who went there (or were prescribed a visit there), even though bipolar disorder was not a clearly defined condition at the time?

Apparently, the mechanism of operation is still unknown.
https://en.wikipedia.org/wiki/Lithium_(medication)

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New Theories / Re: Where should neurosurveillance stop?

« on: 03/04/2018 12:02:32 »

neuromodulation and neuromonitoring of human behavior remotely....
Neuromonitoring and neurosurveillance are basically the same thing.

So how does neuromodulation differ from the other two terms?
Is it more active? More about modifying neuronal activity?

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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.

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Physiology & Medicine / Re: Does an individual's mitochondria disappear?

« on: 02/04/2018 12:37:42 »

I only have sons who have sons am I to understand that whatever of me is physically present on this planet will not continue further? In other words, my only chance of a specious immortality is negated by biology?

The fact that you have children and grandchildren means that part of your genes will continue into the future (but nobody can be confident for how long).
- A sample of your nuclear DNA (3 billion base pairs) has been passed on to the next generation, even if mitochondrial DNA (17 thousand base pairs) has not; 99.9994% participation is pretty successful!
- Hopefully, your experience, wisdom, guidance, training and nurturing have also been passed on to these generations.
- And to the friends of your children, and their families
- Hopefully, you have also had an opportunity to contribute to your extended family, your friends, your community, workplace, the public, and perhaps the country.
- In a wider sense, your contributions to the Naked Scientists forum have benefitted people around the world
- So its a bit unfair to say that you have missed your opportunity for immortality
https://en.wikipedia.org/wiki/Human_genome#Molecular_organization_and_gene_content

Reading between the lines, you might have some brothers who had children?
- They will share much of your nuclear DNA
- Even if you had no children, much of your DNA would be passed on through nieces and nephews.

Even if you were the last of the Romanovs, you share 99.9% of your DNA with other members of the human race, so much of your DNA would be passed on through them - unless/until the human race goes extinct
- The average lifetime of a mammal species is around 1 million years; some pundits forsee a number of challenges just in the next century
- if the human race evolves into something extra-terrestrial and/or post-human, then some of our shared genetic legacy will be passed on through them

But at some level, mortality does seem unfair - I guess that is why Christians celebrate Easter...

12

Cells, Microbes & Viruses / Re: How many cells do bacteria contain?

« on: 31/03/2018 23:43:55 »

There is a popular theory that some interior structures of the  bacterial more complex eukaryotic cell were once separate organisms which came to live within the cell in a symbiotic relationship.
- The case is strongest for mitochondria and chloroplasts, which have their own DNA
- It's not quite so clear for other organelles like ribosomes, which have no DNA, but do contain structural RNA
See: https://en.wikipedia.org/wiki/Bacteria#Cellular_structure
https://en.wikipedia.org/wiki/Ribosome#Origin

Correction: Bacteria → Eukaryotic (thanks, Chris!)

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Physiology & Medicine / Re: Are we in the grip of an opioid epidemic?

« on: 31/03/2018 01:55:47 »

I ran across a podcast discussing this topic.
- The focus is on a young man who played US College Football, suffered a severe back injury and was prescribed fentanyl by a doctor.
- Apparently, about half of his team were on opioids
- If that is typical, then American Football is abusing the very players who make the game popular
- A number of this mans friends became addicted to fentanyl
- This particular young man eventually died from a fentanyl overdose
- They sent an actor to 4 doctors (including the one that prescribed the final, lethal dose), and found that 3 out of 4 did prescribe opioids; these consultations lasted <7 minutes, some of them with no physical examination.

Read the transcript or listen here: http://www.abc.net.au/radionational/programs/backgroundbriefing/prescription-killer:-australias-imminent-fentanyl-epidemic/9180318
When it talks about "fentanyl and its derivatives", I am guessing that it is talking about all opioids?

One problem with opioids is that there is a very narrow window between an effective dose and a lethal dose.
At least with marijuana, there is a wider safety margin...

14

New Theories / Re: Gravitational shift or not?

« on: 29/03/2018 10:28:16 »

there is a possibility that the temperature of the black hole does increase with added mass

You seem to be describing two different temperatures of a black hole:
- The temperature of the event horizon, as described by Hawking radiation
- The temperature of the singularity, which is hidden behind the event horizon
- This is assuming that there is no accretion disk of infalling matter, which radiates heat, light and X-Rays

The event horizon of a black hole of the mass of the Sun has a temperature within a microKelvin of absolute zero. This is very cold.

In physics, if you compress matter, it gets hotter. As a wild extrapolation, if you compress matter into an infinitesimally small volume at the singularity of a black hole, the temperature should be astronomically high. But there are a few problems with this extrapolation:
- At a point at half the radius of the event horizon, the "escape velocity" is greater than c. So no light can escape from this point, or from points closer to the singularity.
- Spacetime inside the event horizon of a black hole is twisted in a bizarre way that makes it hard to compare with our familiar world
- The event horizon prevents us from knowing what goes on inside the event horizon.
- Even if we assume that we can assign a very high temperature to the singularity, it does not affect the location of the black hole, or it's effective temperature.
- High-frequency photons emitted by the singularity would have more mass than lower-frequency photons. This means that higher-frequency photons would lose more energy than low-frequency photons as they climb out of a gravitational well. Even if you doubled the temperature of the singularity (without changing its mass), the event horizon remains at exactly the same radius, and same temperature.

In my primitive understanding of Hawking radiation, it does not originate from the singularity, but from vacuum fluctuations in very close proximity to the event horizon itself.

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

15

Physiology & Medicine / Re: Does an individual's mitochondria disappear?

« on: 29/03/2018 10:04:46 »

If a woman X has a sister, or her mother's sister, their children will have the same mitochondria as woman X.
Thus the mitochondrial DNA of woman X may be passed down through her female relatives.

Bear in mind that a human egg cell has over 100,000 mitochondria, so the exact mix of mitochondria will change from generation to generation. High rates of random mutations in mitochondrial DNA than nuclear DNA will result in genetic changes to the mitochondrial DNA passed from mother to daughter.
See: https://en.wikipedia.org/wiki/Mitochondrial_DNA#Mitochondrial_inheritance

Not every part of everyone's DNA will be passed on to the next generation; even if you have 2 children, on average you will only pass on 75% of your nuclear DNA to the next generation.

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New Theories / Re: Gravitational shift or not?

« on: 27/03/2018 21:59:39 »

You are quite right to say that photons don't change their speed (as seen by someone measuring it in their laboratory).

But observers do change their perception of time depending on where they are in a gravitational well.
- For someone in a deep gravitational well, their time goes more slowly. So they perceive the frequency of an incoming photon to be higher than someone outside the gravitational well. This is gravitational blueshift for incoming photons.
- Similarly, someone outside the gravitational well will have time pass more quickly than someone inside a gravitational well. So they perceive the frequency of the photons as lower. This is gravitational redshift for escaping photons.

Perhaps another way to look at this is from the viewpoint of photon energy:
- A photon has mass
- A photon gains energy as it falls into a gravitational well
- If a photon gains energy, its frequency is higher: This is gravitational blueshift for incoming photons.
- A photon loses energy as it climbs out of a gravitational well
- If a photon loses energy, its frequency is lower: This is gravitational redshift for escaping photons.
- If the gravitational well is very deep - deep enough to form a black hole, the photon loses so much energy as it climbs out of the gravitational well that its energy would become zero and its frequency would become zero. There is then nothing to detect, and light can't escape a black hole.
See: https://en.wikipedia.org/wiki/Gravitational_redshift

Neutron stars are often seen blue.

Neutron stars are extremely small, and often shrouded in the scattered remains of the star that exploded during their formation. Some of them also have a very hot accretion disk, as they consume matter from nearby stars.

They start with an incredibly high surface temperature, hot enough to emit X-Rays, so in that sense I guess you could say that their color is blue.
But this is due to the spectrum of black body radiation, rather than any gravitational effects.
See: https://en.wikipedia.org/wiki/Neutron_star#Mass_and_temperature

Edit: I added the purple text to clarify the confusion I caused below...

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Physiology & Medicine / Re: How do people's brains change as they get older?

« on: 23/03/2018 23:51:01 »

Perhaps I have confused brain and mind, but the following references may be helpful starting points...

fluid intelligence generally declines with age after early adulthood, while crystallized intelligence remains intact

See:  https://en.wikipedia.org/wiki/Intelligence_quotient#Age

Episodic memory starts to decline gradually from middle age, while semantic memory increases all the way into early old age and declines thereafter.

See: https://en.wikipedia.org/wiki/Neuroscience_of_aging
https://en.wikipedia.org/wiki/Memory_and_aging

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Physics, Astronomy & Cosmology / Re: Are distant galaxies receding owing only to space expansion?

« on: 23/03/2018 21:44:41 »

(Oops! overlap with chris...)
Within our own solar system, motion of the planets is dominated by gravity.
Within our galaxy, motion of stars is dominated by gravity, but each star has its own independent speed and direction within the general flow.
Within our local galaxy group,  motion of galaxies is dominated by gravity, but each galaxy has its own independent speed and direction within the general circulation. Andromeda galaxy is heading towards the Milky Way galaxy at about 100 km/second.
See: https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision

The Hubble "constant" is currently estimated at around 73 km/s per Megaparsec.
So to see an expansion that overwhelms the random motion we see between Andromeda and our galaxy, you would need to look at least 3 Megaparsecs away (Andromeda is only 0.8 Megaparsecs away).

It is only when you look at other groups of galaxies that you start to see signs of the general expansion, so the M81 galaxy group is 3.5 Megaparsecs away, and has a recession velocity of about 300km/s.
See: https://en.wikipedia.org/wiki/List_of_galaxy_groups_and_clusters#Closest_groups

The Virgo Galaxy Cluster is 18 Megaparsecs away, and has a recession velocity of around 1100km/s.
See: https://en.wikipedia.org/wiki/List_of_galaxy_groups_and_clusters#Closest_clusters

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Cells, Microbes & Viruses / Re: Could a virus or bacterium survive inside a rock?

« on: 23/03/2018 09:43:23 »

spent thousands of years protected inside this rock in a dormant form, finally be released into the environment when the rock breaks apart (erodes, falls off the side of a cliff, earthquake etc.) and go on to infect a new host?

This is certainly a concern as the tundra melts - it may release new strains of disease organism that have been frozen for thousands of years.

Would it be possible for a particularly hardy pathogen to land on some sediment, become incorporated into the rock

It is unlikely that a surface-dwelling bacterium could be incorporated in rock, and continue living - the change in environment is just too great. Living things require an ecosystem in which to live, and an ecosystem would not survive such a major change.

In tough times, some bacteria (and larger creatures like tardigrades) can go into a dormant state, and then resume growth when the necessary ingredients return - water, food, temperature, oxygen (or lack of oxygen), etc.

But the Desulforudis bacterium was found in a deep gold mine
- It is found as a monoculture, ie it is its own ecosystem.
- It lives and grows in rocks, using energy from the radioactive decay of elements in the rock.
- The fact that it is killed by oxygen suggests that it is not a surface bacterium that got buried, but perhaps one that has been living out its whole existence in deep rocks. (For comparison, some anaerobic bacteria in our gut can produce spores that survive exposure to oxygen.)
See: https://en.wikipedia.org/wiki/Desulforudis

20

Technology / Re: How dangerous are self driving cars?

« on: 21/03/2018 09:38:01 »

in cities where the GPS signal is distorted

Apparently, the cost of GPS chips have come down to the point where sometime this year, some cellphones should be able to start accessing a more accurate timing signal.

This should give much improved location resolution, and much better immunity to multi-path reflections (eg when driving through city canyons).

Unfortunately, due to launch delays, these signals will not provide full coverage until around 2022.
https://spectrum.ieee.org/tech-talk/semiconductors/design/superaccurate-gps-chips-coming-to-smartphones-in-2018
https://en.wikipedia.org/wiki/GPS_Block_IIIA#New_navigation_signals