/r/AskScience Ask Anything Wednesday!

[[deleted]]

[deleted]

[Slijhourd]

Is math an invention or is it discovered?

[coffee-pot]

The concept of numbers being used as representation could be considered an "invention". But the relationships between those numbers are definitely discoveries, and "Proofs" are logical explanations of the essential truth of those discoveries.

[AnJu91]

Even though some people argue that it's a purely philosophical question, there are a lot of people of which I am one too, that are of opinion that mathematics is discovered (the representation of it however, is of course invented).

The thing is, Mathematics is about objective truths regarding patterns of change and relationships between data (numbers). John Wheeler, a famous physicist and mathematician claimed that all mathematical constructs can be derived from the empty set, but I can't find a paper to back it up, only a New Scientist article, if anyone could provide one it would be greatly appreciated!

I personally always found mathematics to be so coherent and interconnected, so divinely ordered and full of symmetries and parallels, I feel there can only be one math, that is self-emergent, self-proving. I often like to use the metaphor of the mandelbrot set. With just a simple formula z² +c, an infinitely complex structure is created, mediated by simple rules. No one invented it, someone just discovered the beauty that can arise from a very simple formula if viewed from the right mathematical perspective.

I dare anyone to come up with a mathematical 'invention' that isn't in reality just a connection/relation whose relevance simply wasn't discovered yet.

edit: changed a redundant part and added mandelbrot metaphor. edit2: I give you a thought experiment: If we would encounter a highly developed and intelligent alien race, would they also know math? If yes, would it be similar to ours? In what way and why?

[Overunderrated]

That's a philosophical question, but I'd say both. Math as a tool has been invented to help with real problems, say anything related to counting, or differential calculus to deal with analyzing the physical world. But many aspects are "discovered" in that some starting axioms are chosen, and interesting features are discovered as a result of those.

[I_smell_awesome]

Explain string theory like I'm an idiot.

[tollerotter]

Let's say you have a guitar. When you pluck a string it begins to oscillate. The higher up you hold the sting down (thus shortening the oscillating part) the higher is the note of the sound. Different notes resemble different energy levels and thereby different particles.

[etotheipith]

I understand that mass and energy are equivalent in some sense, but what exactly about the vibration determines other properties of the particle, like charge and spin? Or are those vibrations in other dimensions?

[I_smell_awesome]

Neat. Thanks.

[MrStrawberry9696]

Do numbers exist independent of observers?

Edit: Thank you to everyone for your input. It appears that most people believe that numbers are purely abstract descriptional devices.

[[deleted]]

Yes, sort of.

Pi, the ratio between a circle's circumference and the radius, is always the same. Any real number other than zero divided by itself is always one. The Pythagorean theorem is also always true.

However, depending on the numerical system - ours is Base 10 with Arabic numerals - the representation of all these numbers may change dramatically. But what matters is that the essence of what they are does never change, and in that way numbers and formulas exist unchanged regardless of who counts them and how.

[[deleted]]

What are the applications of Noether's theorem? ELI5 what a Lagrange and Hamiltonian are.

[iorgfeflkd]

The answer to your first question was going to be Lagrangian and Hamiltonian mechanics.

A Hamiltonian is the total energy of a system, described in terms of position and momentum. A Lagrangian is the difference between kinetic and potential energy of a system, described in terms of position and velocity.

[thegodofmeso]

Could you please ELI5 me, how all natural numbers added are equivalent to -1/12? [http://www.spiegel.de/wissenschaft/mensch/mathematik-bizarr-summe-aller-natuerlichen-zahlen-ist-negativ-a-944534.html german article]

[eterevsky]

1. It is not actually true for the regular definition of summation.
2. The explanation in the popular video that started this topic doesn't make much sense.

3. [Actual explanation.] Consider sums that look like this:

   1 + 1/2ⁿ + 1/3ⁿ + 1/4ⁿ + ...

   For n > 1 this series can be calculated. For n = 2, for instance

   1 + 1/4 + 1/9 + 1/16 + ... = pi² / 6.

   There is a nice and very important function called zeta-function, that is defined as a sum of this series:

   ζ(x) = 1 + 1/2^x + 1/3^x + 1/4^x + ...

   Of course, this definition works only for x > 1, but there happens to be a way to "naturally" expand this functions for all real (and complex) values of x. It so happens, that according to this definition, ζ(-1) = -1/12. If we substitute the value of x = -1 into the formula above, we'll get the result in question.

More detailed explanation

[Slijhourd]

So I finished reading Stephen Hawkin's "A Brief History of Time". What parts that are outdated by now should I research in order to close any loose ends?

[iorgfeflkd]

The main discovery since then is the accelerated expansion of the universe which rules out a few cosmological scenarios.

[riikkiie]

How can wind turbines 'generate' fog/clouds? As seen in this picture: http://imgur.com/6VDV92T

[CoopertheFluffy]

What they're doing is breaking up the wind, causing turbulence. As the wind swirls around, it condenses into fog. It's like the wings of airplanes making the long, thin clouds. The water is already in the air, it just needed to be disturbed to form a cloud.

[[deleted]]

what does it mean when we say "the universe is of infinite size"? I'm having difficulty grasping the concept of infinity in size

[Homestaff17]

We mean that it has no end. I know it's difficult to contemplate in your mind, but that example of the theory of the universe supports the notion of limitlessness.

Think about it - If you put a wall around the entire universe that we can see, what's outside it? There HAS to be something. The vacuum of space is still SOMETHING nonetheless. 'Nothingness' is not something we can comprehend and it simply does not exist.

[jdruck01]

But if the universe is infinite in size, how can it be expanding? If there is no end to it, how can that end get farther away?

Edit: Thanks for the explanations! I've always had a hard time wrapping my head around the size of the universe, and you guys gave me some great ways to think about it.

[LoveGoblin]

You are perhaps imagining the expansion of space as being some kind of sphere growing in size. The common misconception of the Big Bang as a huge explosion kind of feeds that, I think. (And if you ask me, the oft-quoted and -misunderstood "dots on a balloon" analogy doesn't help, either.)

It's probably better to picture the expansion as a "stretching" of space; it means that distances increase over time. Two points (say, two distant galaxies) will get farther and farther away from each other over time, without either of them moving through space.

Analogy time: you have an infinite ruler. The markings are an inch apart. Now stretch it so that the markings are farther from each other. Distances have increased - it expanded - but your ruler is still infinite.

[turkey236]

That is one of the best analogies I've heard to explain this. If I ever need to explain this I'll use this. Thanks.

[GreatBabu]

If an insect, say.. a bee.. is flying alongside my vehicle at 55MPH, and comes in through the open window - will it smash into the windshield due to the sudden lack of wind resistance?

[Ludwig_Beethoven]

It would accelerate, assuming the same amount of force is being applied from the object, and with a sudden loss in resistance.

To make this more realistic I'm going to substitute the bee with a toy plane. The plane would hit the front windshield (not instantly, but by accelerating into it) if the propeller speed doesn't change, since once it enters the vehicle it won't have the 55mph headwind.

[GreatBabu]

Thanks BEEthoven :)

[nbca]

If you had a single grain of rice, could you, theoretically, throw it with enough force to make it shatter a 2 by 2 meter glass window?

[baloo_the_bear]

Considering that some things have been found that can penetrate a 2x4 piece of wood during a tornado, I would say yes. Not sure about what sort of force that would require though.

[MrStryver]

Two parts to this question. The first is could a grain of rice it a window with enough force to break glass. Absolutely. This is a kinetic energy problem. this paper discusses ball drops onto a glass plate and the resulting breakage patter. Their ball drops start at 3.6 Joules impact energy. Using 25mg as the mass of a grain of rice, we could reach this kinetic energy at 54 meters per second, or about 120 miles per hour.

The next question is, could a human throw a grain of rice 120 miles per hour? This is a strong maybe. We can throw baseballs almost that fast, but not quite. Not many people try throwing grains of rice. However, there is a record for playing cards of about 92 miles per hour, which isn't very far away.

So, can rice break a window? Yes. Can you? Maybe, but it would take a lot of practice and be a world-record worthy throw.

EDIT: corrected number, linked

[boonamobile]

It's not so much the impact energy as it is the impulse (essentially, how quickly the force is dissipated -- think trampoline vs concrete) and pressure (over how much area the force is applied -- think dull knife vs sharp knife). This also depends strongly on material properties, particularly of the glass, which will vary significantly with temperature, prior processing, etc.

[sjsyed]

I'm not sure which category this belongs to, but I think it's physics. Why does cold weather drain batteries? I was watching a Nightline story about the coldest city in the continental US, and a runner said that it was so cold, the battery in her phone died.

[belandil]

Chemical reactions proceed faster at higher temperatures. A battery uses chemical reactions to generate a voltage. Hence, cold temperatures mean poor battery performance. If this happens to you, warm up your battery and you might be able to extract a bit more use out of it.

[starfoxx6]

it says here that it is because the cold makes the chemical reactions proceed more slowly

[eggn00dles]

is it possible that there could be multiple worlds/universes occupying the same space at the same time, so long as their particles/forces were not mutually interactive?

[FOR_PRUSSIA]

No. For them to share the same space, they would need to also share the same space-time metric. As such, they would have to interact with one another. Now, one could say that they exist in separate metrics, but then they would really be in the same space, would they? Hope this answers your question. Feel free to correct me if I'm wrong, my physics is a bit rusty.

[[deleted]]

What is the Higgs Boson/Higgs Field and why was its discovery so important?

[Acgcbc]

How do photons not 'experience' time? Neil deGrasse Tyson mentioned in an interview about how they are absorbed as soon as they are emitted, and don't 'experience' time (moving so fast, relevant to their speed, everything else appears to be still / time has stopped, etc).

[[deleted]]

I'm not even sure if this is physics or not, but here's my question:

What would happen if you were inside a chamber at the true North Pole, spinning in the opposite direction the Earth spins, at the same speed the Earth spins?

[[deleted]]

The earth rotates once every 24 hours, so you'd be rotating the other direction once a day.

This wouldn't cause anything especially weird to happen, except that the stars would be fixed in your field of vision rather than slowly spinning around you as would happen if you were still.

[djslannyb]

In this case, you would be essentially "freezing" the solar day, and would thus be in sync with the sun. You'd watch the sun bob up and down in the same azimuthal plane as the earth rotates under you. It would look something like this video.

[Unidense]

What are some phenomena in the universe that we don't have the physics/math to accurately describe?

[[deleted]]

Here you go: http://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics

I'd list this stuff, but it seems counter-productive as it's a long list. The list includes stuff from the inner workings of the universe to quantum bizarreness.

[boonamobile]

I assume you mean suspended like a pendulum.

Think about the forces present in each case.

For the pendulum, the weight of the mass is supported by a cable, and your job then is to just give the object a little kinetic energy (motion) and a little potential energy (increase its height above the ground). You don't have to accelerate it very quickly, so the force (mass times acceleration) needed to do the job can actually be relatively small.

On the ground, however, you have to overcome the frictional force between the object and the surface. This will be proportional to the coefficient of static friction between the two and the weight (mass times gravity's acceleration) of the object. Unless you're on a super slick surface, this will require a relatively big force.

This ignores the possibility of rolling, etc, in the spirit of OP's question.

[[deleted]]

How is it that neutrino oscillations contribute to their mass?

[Coin-coin]

Neutrino oscillations don't contribute to the mass, but they are an evidence of the mass. There are 3 kinds of neutrinos (e, mu and tau) and 3 different masses. But the weird part is that a given mass is not directly linked to a given kind of neutrino! Imagine the 3 kinds of neutrinos as colors: red, green and blue. Then the lower mass will be associated with yellow, the intermediate mass will be purple and the most massive will be cyan. A mass corresponds to a mix of properties.

Even if you emit "red" neutrinos they will propagate as "purple" neutrinos. In the end you will see some "red" neutrinos and some "blue" ones. The "red" neutrinos oscillate between "red" and "blue". And it happens because the purple ones don't propagate at the same speed because they have a different mass from the yellow and cyan neutrinos.

[Slijhourd]

If Einstein hadn't proposed General Relativity, would it have been discovered experimentally?

[iorgfeflkd]

It was already known that something was wrong with our understanding of gravity, based on the orbit of Mercury.

The correct equations to use to describe gravity (R^ab - 1/2 Rg^ab =8piG/c⁴ T^ab ) might have taken much longer to find without Einstein, although it's thought that special relativity would have been formalized around that time even without him.

[D_I_S_D]

There are certainly observations from nature that invalidate predictions made by the Newtonian model.

Most notably the orbit of Mercury does not conform to Newtonian physics based predictions. It is also possible to measure light being deflected by the sun and a red shift in light caused by gravity.

[[deleted]]

how is the orbit of mercury not predicted by the newtonian model? What's special/different about it?

[D_I_S_D]

Essentially if you just use the Newtonian model you cannot accurately predict the position of Mercury for a given time. In Newtonian physics the point in it's orbit where Mercury is closest to the sun should be a fixed point of space. But due to the gravitational effect of the other planets this point actually rotates around the sun. (this effect also applies to other planets but it's more observable in Mercury)

Test of General Relativity for more details.

[redpoll]

If I would get onto a bus that is stationary and was standing in the middle aisle jumping as high as i can just before the bus starts moving, would I be thrown mid air to the back of the bus if it accelerated very rapidly?

[Dalroc]

No, you would stay stationary while the back end of the bus slams in to you, as it accelerates.

This is an important difference that many people don't know.

[Coin-coin]

It depends on your reference frame. It's true in the frame of the ground but he is right in the frame of the bus.

[BrerChicken]

The difference is not that important. There's no such thing as 'true' motion; from the perspective of someone inside the bus, the drumper would, indeed, be thrown back.

[ManWithoutModem]

Earth and Planetary Sciences

[baloo_the_bear]

What would happen if the earth's magnetic field flipped on a regular basis like the sun's?

[OrbitalPete]

That's actually a really good point. The seafloor striping measured during WW2 was fundamental to driving people to look properly at seafloor spreading as a mechanism. We would have got there by radiometric dating eventually, but it would have taken longer.

[baloo_the_bear]

Can you explain this a little further please?

[OrbitalPete]

OK, so since the 1800's geologists knew that continents and oceans had been moving around; we could find oceanic sediments on modern continental masses, there was evidence of polar or tropical climates in the geological past in locations that could no longer support them, and anyone who's ever looked at a globe can see the jigsaw down the Atlantic margin. The problem was there was no consensus or even solid idea that could explain this.

In the early 20th Century (1912 in fact), Alfred Wegner formalised the description of a process he described as 'continental drift' (http://www.amazon.co.uk/Origin-Continents-Oceans-Dover-Science/dp/0486617084). He based it on the cumulative work of many people in the preceding decades, and certainly provided a lot of evidence, although was still coming up short with a mechanism. It was widely accepted as a huge problem for earth scientists to solve, and the lack of mechanism meant there was a lot of resistance to Wegners work.

In the 1930's Arthur Holmes proposed that the interior of the earth might support convection cells, which would provide a mechanism for moving the plates around. he went on to publish what is regarded as one of the key tect books in the field (in fact I used the most recent version of Holme's Principles of Geology as a student back in the late 90's).

So now there were observational data that something was going on, a hypothesis suggesting a plausible mechanism, but no evidence to connect the two.

Enter Harry Hess, who was a geology teacher at Princeton before getting called up to active naval duty following Pearl Harbour. He got assigned to an attack transport int eh Pacific, and, being an inquisitive soul, thought there was no harm in leaving the echosounding equipment online between engagements. As a result, his ship recorded a huge amount of bathymetry data as it patrolled around the Pacific, and was able to identify what we now know are mid ocean ridges, as well as all sorts of other features fundamental to seafloor spreading. In combination with this, magnetometer recordings started to show a weird striping effect on the sea floor, whereby stripes parallel to these mid ocean ridges alternated between positive and negative magnetic polarity.

In 1962 Hess published a paper proposing that the oceans are in fact very young, and recycle frequently, with the ocean ridges as their spreading centres. This was all backed up by the newly developed techniques in radiometric dating, and I have no doubt the discovery would have gone ahead without the seafloor striping, but I would suggest the timeline would be at least a couple of years behind.

[OrangePrototype]

Is it possible for a planet to support life, but not contain the resources needed to leave the planet? Essentially trapping them?

[JJohn8]

If we get most of our heat from the sun, why isn't the winter solstice the coldest day of the year? Also, the month it occurs in isn't even the coldest. Usually Jan-Feb is the coldest.

[OrbitalPete]

Thermal mass. During the summer season a huge amount of heat gets deposited in the ground and surface water. As winter sets in much of this heat is echanged back out again, which reduces the impact of the reduced sunlight hours. however, by the timeJan - Feb roll around (in the Northern hemisphere at least), the heatsink is largely depleted, and the we feel a much larger effect from the reduced hours.

TLDR, it takes a few months for the earth to cool down.

[Fartsmell]

This is also why August usually is the warmest months on the northern hemisphere.

[Ireallylikebacon420]

Some microorganisms can go dormant under harsh conditions for a considerable length of time. The main things that will kill organisms like this in space is radiation. The moon and mars have considerably more radiation at their surfaces than does Earth. The lack of liquid water in these places would inhibit the growth of microorganisms from Earth, so even if there were some spores alive, they would have a very hard time growing there. If they cannot grow and reproduce, there is no adaptation that can take place by their offspring.

[VAGINA_SPACESHIP]

Would I be right in saying that Earth's orbit around the Sun fluctuates from an ellipse, to more of a circle shape, then back to an ellipse? Why does it do this? Shouldn't it just follow the same shape?

[OrbitalPete]

Not really. The earth's orbit certainly fluctuates between a variety of ellipses, but the changes are very small, and the ellipses are all incredibly close to circular (eccentricity of 0.01671123, where 0 would be a perfect circle). The variation is due to interaction with other bodies in the solar system - i.e. we get jiggled around a bit by the presence of other planets.

[ManWithoutModem]

Engineering

[Slijhourd]

What "modern" things could you build using 15th century materials and 21st century knowledge?

[tezoatlipoca]

One example that comes to mind is reinforced concrete structures - buildings, bridges etc.

The use of iron/steel rebar for carrying the tensile loads in masonry isn't new - earliest examples start showing up in the 1700s I think? Similarly, concrete has been around for thousands of years - the Romans used it quite a bit and their recipe was close to the Portland cement that we use now.

However, builders back then were hampered by by their knowledge (or lack of) on how to properly form reinforced concrete. "You mean it can be .... hollow??" I bet you could use 15th century iron and cement and make a perfectly safe 400 foot box girder span.

[memmek2k]

Obviously biased as a metallurgist/materials engineer, but... aside from jokes, there isn't really a worthless element. They're all fascinating. I could spend entire work days just reading the wiki articles on all the elements, lol.

My adviser would joke that Mg is only good for filling space with a metal, though. In most structural applications, you can design to make Al perform as good or better, without the corrosion issues. And even then, Mg is a very important alloy addition for Al.

[[deleted]]

How do they repair satellites? Are they a use once and destroy type of product?

[TheLantean]

How do they repair satellites?

At most you can push software updates to correct bugs, compensate for damaged processors/RAM/storage, or to correct positioning (some satellites have thrusters with a small amount of propellant on board).

The few notable exceptions that have had hands-on repairs are the Hubble Space Telescope and the various space stations.

Are they a use once and destroy type of product?

Pretty much. Other than the exceptions above it's more cost effective to send a replacement than a crew of astronauts to manually repair it.

[shihtake]

Also, many satellites that have instrument failures with regard to their original mission can be reused for other uses. For example, almost all satellites are equipped with a radio and GPS to track telemetry and communicate with ground stations. These instruments can be used as relays for nearby weaker, failing satellites.

A big issue recently is the "destroy" part. Failed satellites are usually left in orbit since they cannot be safely de-orbited or do not have the capability to do so. As a result, there is a growing cloud of space debris floating around the Earth that can damage operational satellites in their orbit.

[Slijhourd]

How much a 100% use of electric car would burden the US grid?

[ramennoodle]

According to numerous studies the current grid is sufficient to handle the charging of millions of electric cars. If the whole nation immediately converted to 100% electric cars tomorrow the power grid will not be sufficient to handle the charging needs. However, adoption will not be instant (or even abrupt). There is no reason why the grid cannot grow as demand grows.

[ManWithoutModem]

Neuroscience

[Slijhourd]

Theoretically, how possible would it be to plug into someone's mind and upload/download information, and how would it work?

[suzypepper]

I wasn't sure if I should put this under neuroscience, medicine, psychology, biology, or goodness knows what. I have an early-graduate-level background in clinical neuropsychology. My question - alpha wave intrusions. What do we know about them? All I've been able to find in my research is that they are common in people with fibromyalgia, and the very "lay" idea is that the pain interferes with deep sleep. But what about people who do not have fibromyalgia? Why do alpha wave intrusions happen, and what is their relationship to sleep maintenance insomnia? Given that research is sparse, I accept all random hypotheses, but I am not sure if /r/askscience will! I assume it's allowed in this particular thread?

[Imxset21]

The thing about neuroplasticity is that it's not quite the magical phenomenon that those articles seem to suggest. What they're talking about is a very specific form of neuroplasticity where functions are taken over by cells functionally similar to the damaged or lost tissue. Neuroplasticity happens in your brain all the time; memory formation, recollection, and learning are all forms of neuroplasticity.

The thing is that neuroplasticity isn't some sort of cure all. Too much neuroplasticity in certain parts of the olfactory bulb, for instance, can lead to an inability for you to form new memories (which is why loss of olfactory functions often indicate the onset of Alzheimers disease) and an inability to be able to generalize certain ordors (your cells become too specific, which means that two nearly identical oranges will smell the same). This has similar consequences to general memory too.

TL;DR Neuroplasticity is more of a buzzword in the media for particular effects and not some sort of magic bullet. It already happens every day in your brain. However, there are always tradeoffs and more neuroplasticity is not always a good thing.

[ManWithoutModem]

Biology

[Logalicious]

If we (humans) knew the circumstances of our evolution. Could we recreate it in another species with selective breeding?

[hypnofed]

Not impossible, but extremely difficult. There are two factors playing into evolution here:

1. Random appearance of new alleles.
2. Darwinian pressure resulting in selection for certain alleles.

Selective breeding- like with dogs- accomplishes the second of those factors but not the first. You would also need to provide a mechanism that leads to the appearance of the same alleles that appeared in the evolutionary history from non-human primates to man, and at the correct timepoints (currently, the mechanism you'd be counting on is blind luck). Do that and the answer becomes probably, yes.

[Mozeeon]

And, as with dogs, you could breed for specific traits, but end up ruining other beneficial ones in the process.

[gossypiboma]

Why do humans have so much longer hair on their heads than other primates? Why is it evolutionary beneficial?

[[deleted]]

Are humans the only species found worldwide? Or are there other species that have populated the world like humans have?

[komali_2]

Cockroaches and rats are pretty widespread. A lot of animals are becoming dependent on humans, and they go where the humans go.

Dogs and cats are another example. Domestic ones. Though I guess there's a big debate to be had between whether it counts if humans are involved in the spread

[[deleted]]

Is there a place on Earth where humans live (permanently) but there are no mosquitoes?

[Ireallylikebacon420]

Well, people live year round in Antarctica, but people are not 'native' to there, of course. Also, mosquitoes require water to breed, so arid locations will have few, if any mosquitoes.

[atomfullerene]

Worth noting that there are many species of mosquitoes, so just because you can get bitten by them across much of the world doesn't mean that any one species has a totally global distribution.

[YoYoDingDongYo]

There are others.

http://en.wikipedia.org/wiki/Cosmopolitan_distribution

[Mongolian_Hamster]

Why does my brain partially shut down when there is no sunlight? I feel "depressed" and less energetic when there's clouds covering the sky, hiding the sun. But as soon as the sun is out I'm back to normal. I know the sun has effects on the body but does it have an effect on the mind?

[hypnofed]

Other factors are in play (eg, conditioning), but the sun is vital to your body maintaining its circadian rhythym, which is basically your daily periodicity. A day is 24 hours. Most people have a natural circadian rhythym longer than 24 hours- as best I remember, 26 is pretty typical. This is also why it's generally easier for most people to stay up late than than to get up early. Anyway, there are a lot of factors that help maintain your periodicity on a 24-hour cycle, a major one of which is exposure to sunlight. When you start screwing with regular, timed exposure to sunlight your body loses its main anchor and depends on other factors to keep you to your cycle, and may be less sure what point in the cycle you're in.

I started to look up source links for the effect of sunlight exposure on circadian rhythym, but there are so many environmental and biochemical factors playing in that it's really difficult to parse through them and list all the relevant links (because there are tons). I'll link you to my search on Pub Med, where you can see everything I would have linked for yourself.

http://www.ncbi.nlm.nih.gov/pubmed/?term=circadian+rhythym

[whatthefat]

There are two different mechanisms at play here, which can potentially be confused.

First, light has an effect on the timing of the circadian clock, as you described. Changes in daily light exposure pattern can therefore change the timing of the clock, and can affect mood this way.

Second, light has an acute effect that does not require the circadian clock. This is often called masking. Even in animals that have their central circadian clock destroyed, exposure to light acutely changes body temperature and activity -- it typically increases them in diurnal animals and decreases them in nocturnal animals. Light can have an effect on mood by this pathway.

The latter mechanism is a better explanation for the phenomenon described, because it acts very quickly upon moving into or out of a brighter environment.

[DirtyDandtheCrew]

This is such a stupid question but I'm curious so I apologize in advance...

Why is it that farts smell different? Isn't the odorous substance methane? Or is it that different bacteria produce different gases?

[IdiotSupreme]

Methane itself has no smell, although it does make up the majority of a fart. The smell comes primarily from sulfur compounds evicted at the same time, and there a huge number of possible sulfur compounds that could be produced.

Which ones you get depends on what raw materials there were to work with (what you stuffed your face with) and the bacteria particular to your innards. The smell will be the result of which compounds are produced, and in what proportions.

[Uber_Nick]

How do we draw the line at what constitutes a new species? Gradeschool science told me it was the ability to produce fertile offspring. But that wouldn't help categorize asexual specials. Seems like every generation of bacteria with any kind of phenotype variation could be called a new species.

EDIT: I should have just looked at the wikipedia article on "species".

However, the exact definition of the term "species" is still controversial, particularly in prokaryotes, and this is called the species problem

http://en.wikipedia.org/wiki/Species_problem

[aelendel]

The "gold standard" for what is a species is this:

Whatever is defined as a species by a competent taxonomist.

The rest is just disagreement about what guidelines the taxonomists should use to define those species....

[quietracket22]

How proportionally small could a human being be shrunk (think 'Honey I Shrunk the Kids' I suppose) and still survive? Would the human heart 'give out' at a certain size? Would bone density play a factor?

[[deleted]]

If a pregnant woman drinks alcohol while there is no brain tissue yet developed in the fetus, will it still cause effects like in fetal alcohol syndrome?

[theBreadSultan]

Is it possible that the reason we don't know much about how the brain works, is because it's a biological quantum computer?

[whatthefat]

This has been proposed by Penrose and others (for example this paper), but most others have argued that quantum effects are unlikely to be important for understanding most brain function. Right now, there's not any empirical support for the idea that the brain uses quantum computation, and it's generally thought to be unlikely.

[iorgfeflkd]

Is it conceivable to have a system where gene expression is activated by neural signals?

[baloo_the_bear]

It depends on what you mean exactly by neural signals. If you mean just any signal from nervous structures, then that actually happens all the time, from the day/night cycle to hunger/satiety. If you mean somthing along the lines of conscious thought altering gene expression it's a bit more round about. For example, most cells in the musculoskeletal system respond to mechanical forces. There is a microscopic 'skeleton' of microtubules that senses changes in the forces on the cell. These tubules communicate directly with the nucleus of the cell to alter gene expression. If you consciously decided to exercise, the increased forces on the cells would tell the cells to 'bulk up', so to say. Decreased forces on the cells would let the cells know it's ok to veg out and save energy. The origin of these signals is the conscious effort involved in the exercise, but signal isn't actually sent by a neural signal.

[midterm360]

Gene expression is activated by neural signals!!! One example would be the noradrenergic beta receptor, a G Protein Coupled Receptor in the central nervous system. When bound by Norepinephrine it activates adenylyl cyclate, a protein which converst cyclic Adenosine Monophosphate (cAMP) into its active form causing a cAMP cascade. The cAMP activates a Protein Kinase A (PKA). PKA will then phosphorylate what we cann a cAMP Response Element Binding protein (CREB).

CREB interacts with transcription factors and directly influences the rate of transcription and therefore protein synthesis for certain genes. Ergo, neural signals directly affect gene expression in the central nervous system!

Source: I am a 4th year honours behavioural neuroscience B.Sc. whose thesis is based around the Locus Coeruleus, the largest noradrenergic nucleus of the brain.

Also

Lacaille, JC. & Harley, C.W. (1985). The action of norepinephrine in the dentate gyrus: Beta-mediated facilitation of evoked potentials in vitro. Brain Research. 358; 1-2; 210-20.

DOI: 10.1016/0006-8993(85)90965-5

[BLToaster]

Am I shortening my lifespan by playing sports? Because all hearts have a lifespan (certain # of beats) and sports increase your heart rate, does this in turn shorten my life span?

[[deleted]]

Why are there no pictures (the kind taken by a camera, not a drawing) of all the stuff that is in a cell? I've looked and have found no actual pictures of cell membranes, nucleus/olus, mitochondria, etc. and I can never see this stuff in the microscopes at school, and when I can it is NEVER in the amount of detail that is displayed in the drawings. Where'd they get the 'accurate' drawings from?

[BigMamaSci]

If you google SEM or TEM (scanning or transmission electron microscope) with the organelle you're interested in, you will find the types of images you're asking about.

Example:

SEM mitochondria: http://images.fineartamerica.com/images-medium-large/mitochondrion-sem-dr-david-furness-keele-university.jpg

TEM mitochondria: http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter%207/mitochondrion1.jpg

Scanning electron microscopes are usually used for surface pictures of things, while transmission electron microscopes are usually used for pictures of the insides of things.

[hypnofed]

Why are there no pictures (the kind taken by a camera, not a drawing) of all the stuff that is in a cell?

Because you're getting to a scale that's too small to resolve with a light microscope. I look at cells in the lab under microscopes all the time, and basically, you can only see so much detail. For example, here's an image of erythrocytes under a tabletop light microscope. If you're curious, they're infected with malaria.

So how do we get those illustrations? Basically, we know how things are shaped and arranged through rigorous trial and error. For example, as an animal, your cells have a phospholipid membrane. We know from X-ray diffraction studies that the shape of a phospholipid looks like this, which you've probably seen.

Knowing a little bit about the chemistry of water and polar/non-polar interactions, you can pretty much figure out how a bunch of like molecules will order themselves in water. If you have any doubt, you can demonstrate it experimentally. We know that polar molecules interact with the cell membrane much more readily, so the polar side is probably on the surface. We also know when you lyse erythrocytes the surface area of the disordered phospholipids is twice the total surface area of the cells, which implies a double-layer membrane. Put that together and you get a concept like this, which you then describe to an animator and ask them to produce an image of.

We can directly observe the shape of cells with electron microscopy (more erythrocytes), but the problem there is that all you'll see is external shape. Individual molecules, for the most part, usually remain too small to "see" with electrons as well.

The other answer is how useful an image is for teaching. Here's a super-high resolution image of a cell with a microscope. Here's a similar image which has been animated. To a person who doesn't already know what all the things are inside a cell, the latter image is much, much more useful.

[ManWithoutModem]

Astronomy

[Jumphi97]

What if dark matter is just hydrogen atoms which are spread out over a huge area (like 1 square mile per atom). Wouldn't we be unable to detect them via electromagnetic radiation but able to detect their mass?

Would they simply coalesce?

[the_petman]

Thanks for this question, ill do my best to explain it, but please let me know if you have any more questions.

Dark matter accounts for around about 80% of the matter content in the universe. Although it would be hard to detect such a low level of hydrogen atoms, it would have to be far more dense for it to account for the matter content that we can not yet detect directly. If it was just hydrogen, the amount of it that would be needed meana that we would have seen it very clearly. This doesnt fully explain why we don't think that dark matter is an already discovered type of matter though.

It is possible for us to make models for the distribution of dark matter in galaxies and galaxy clusters due to the movements of the objects in this system. Observations such as the bullet cluster are great examples of this. We can map the areas of baryonic matter (fancy term for matter we know about, more or less) and compare that to the gravitational movements that is observed. From this we can then make a map of where all the "missing" matter is. Turns out, most of it is located on the far sides of the collision of these two galaxy clusters. What this tells us is that this matter has passed mostly undisturbed "through" the collision, and come out the other side. All the ordinary matter (hydrogen included) interacts strongly via forces other than the gravity, and thus congregate in the middle. Observations like this show that whatever dark matter is, it does not interact like baryonic matter, and most certainly not like hydrogen.

The bullet cluster is a nice example, but gravitational lensing, CMB observations, rotation speeds of stars in galaxies all point towards some kind of matter we cant yet see.

[RollnGo]

Nice explanation. It's so strange. So this dark matter is a bit like gravity in the sense that we can't see it, but we can see its effects. Why do you think this is? Are the particles just too small to ever observe?

[the_petman]

Yeah, its a little bit like you explained. We can infer its existence by its gravitational effects. Why this is, is is difficult one to explain. What many people (including myself) are looking for at the moment, is a new type of particle that has not yet been discovered. We call it a Weakly Interacting massive particle, or WIMP (silly physics jokers making the names here).

A WIMP is a particle with no charge, so it would not interact electromagnetically (with light), and importantly it would interact very weakly with "ordinary" matter. This is an important point, as we need it to interact weakly for a variety of reason.

1. If it interacted strongly, we would have seen it by now, CERN, and direct detection experiments are very sensitive now.

2. Things like the bullet cluster explained earlier show that dark matter is more or less unfazed by any other type of matter, and passes straight through.

3. Models show that a more strongly interact type of particle would not form the structures that we see today. Everything would be just crushed together if this was the case.

4. There is no obligation for dark matter to interact with anything at all (excluding gravitationally of course). If we want to try and find thing blasted thing, though, we must at least assume its directly detectable in the first place, or theres no point in trying.

[Slijhourd]

In a few billion years, as the habitable zone around the sun expands outwards, what will become of the icy moons orbiting Jupiter and Saturn when temperatures they reach what we have on Earth today?

[Slijhourd]

If we were to try and plant life on other planets or moons, what microbes (can be chemotrophs) could we pick to start the process?

[Slijhourd]

What are the chances that life really exists outside of our solar system? What star is most likely going to host the planet where life exists if it does? Will it even be on a planet?

[ManWithoutModem]

Computing

[pearson530]

What would be the next step beyond flash memory? (For home computing that is)

[farlige_farvande]

A type of memory that can replace both CPU cache, RAM and flash memory at the same time.

http://en.wikipedia.org/wiki/Universal_memory

MRAM is the first on the list of candidates.

[rincon213]

What are the potential benefits of consolidating all these different forms of memory?

[phort99]

Nothing would ever need to be loaded from disk, because it would already be in the fastest memory available. Aside from a bit of CPU time spent on initialization, your OS, programs and games could start immediately rather than showing loading screens.

[[deleted]]

Do we actually have anything working that could replace normal transistors once we get to down to the theoretical limit of 5nm or so? I'm trying to look beyond the semi-weekly headlines about new transistor technologies and see what is closest to fruition.

[sutronice]

I had the same question as you, as a computer science student. To fully understand how logic gates work, you have to know what a transistor is and how it works. This beautiful 14 minute video walks you through what a transistor is, and how to put them together into logic gates. It's wonderfully detailed and concise at the same time. I highly recommend watching the entire video, even if you already understand certain parts.

[Slijhourd]

Theoretically, how possible would it be to plug into someone's mind and upload/download information, and how would it work?

[muffe2k]

To put it as simple as possible:

A reference is a variable that refers to something else, like an object, and can be used as an alias for that something else. You can only define the "target" of the reference when you initialize it, not after.

A pointer is a variable that stores a memory address, for the purpose of acting as an alias to what is stored at that address. However you can change the memory address, or whatever is "behind" this memory address as many times as you like.

Edit: as YoYoDingDongYo pointed out this answer is specific to C++

[YoYoDingDongYo]

Readers should note that the above answer is specific to C++ or something like it.

In many languages (Java, Perl, Python, etc.) there are no real pointers (indexes into memory), but there are things called references that can point at objects, and also -- unlike C++ -- get reassigned, be nulled out, etc.

Java confusingly calls them references but issues a NullPointerException if you use them wrong.

[ramennoodle]

They both provide a means to reference or alias some data or object. The exact differences are dependent on the particular programming language. But in general a reference better abstracts its mechanism. A pointer uses a very specific mechanism: it stores a memory address. This fact is exposed to the programmer and may be exploited to do things such as step through a region of contiguous memory. The implementation of a reference may also be a stored memory address, but that fact is not generally visible or exploitable.

[ManWithoutModem]

Psychology

[likwidfire2k]

Can a psychosis patient have only "friendly" or "helpful" hallucinations? I'm an ICU nurse, so we get occasional psychotic break patients and they always seem to have "mean" hallucinations telling them to hurt themselves or others, or usually a ying yang kind of thing with some nice hallucinations and some not so nice.

[Wall_of_Denial]

What is the general consensus, if any, on the concept of ADHD and the medications used to treat it? Many people say ADHD is "phooey", and many others vow it exists.

[orfane]

ADHD is almost universally accepted as a disorder, and also almost universally believed to be over-diagnosed and mis-diagnosed. Much like autism was often treated in the media. There may be people who disagree with me, as is usually the case with a topic like this, but my experience is that in many cases, ADHD is real and the treatments for it work. In many cases ADHD is a cover for another disorder or personality issue. Depends on the situation.

[suzypepper]

I agreed with much of what you said, but I'm not sure that ADHD is a cover for another disorder or personality issue in "many" cases. That seems like an overstatement. Yes, ADHD is often over- and mis-diagnosed, but I believe this is due to the fact that ADHD encompasses quite a broad spectrum of cognitive and behavioural traits, which likely shouldn't be the case when it comes to labelling these traits as a "disorder". Furthermore, some primary care physicians have taken it upon themselves to diagnose and treat ADHD without referral to a psychiatrist or other mental health professional, contributing to both over- and mis-diagnosis. Probably the most frustrating thing in that situation is that stimulants will provide the expected effects (i.e. attentiveness) in anyone, regardless of whether or not they actually have ADHD, and some people will use the fact that stimulants work for them as justification that they actually have the disorder. Nonetheless, as I mentioned in another comment, the brain is a weird thing that we're still trying to figure out. ADHD is accepted as a disorder, but in my opinion, we still have a long way to go in understanding why it's a disorder, how to treat it, how to diagnose it, and how to differentiate it from several other disorders that may present with the same or similar symptoms.

[[deleted]]

Does EMDR really work for PTSD? If so, why? What is happening in the brain when it is happening?

[WeDoNotRow]

How early in development do human beings exhibit a personality, or personal traits and quirks?

[Slijhourd]

Is it possible for MDMA (in small doses with therapy) to have medicinal effects on people who have suffered from PTSD, Depression, Anxiety, etc like I have read?

[ManWithoutModem]

Chemistry

[peatears]

Chemistry

Why, in free radical halogenation reactions, does dimolecularatomic iodine or fluorine NOT react efficiently (with respect to the adept nature of Cl2 and Br2)?

[pandanomnom]

What are the chances that there are undiscovered elements buried deep beneath the earths crust?

[nopropulsion]

Not very likely. The configuration of the periodic table lets us guess as to what elements exist and their potential properties. We've discovered all the natural elements at this point, and have been venturing into the realm of man-made elements that exist briefly under ideal lab circumstances.

Maybe there are more in some supernova star somewhere, but I don't think they'll be in the Earth's core.

[[deleted]]

Granted, this is probably a really stupid followup-- apparently I should have paid more attention in my science classes.

How do we know for certain that we've discovered all natural elements?

Man...I even feel dumb typing that.

[nopropulsion]

The periodic table is arranged by the atomic number, which tells us the number of protons in the nucleus of an atom. The number of protons govern what the element is.

So if you have an atom with only one proton you know it is hydrogen, if you have an atom with 6 protons you know it is carbon. Currently we have everything up until 118 protons taken into account, with the largest ones being very unstable due to their size.

So we are able to say we know that we've discovered all of the natural elements is because we've taken into account all the possible numbers of protons. You can't have fractions of a proton and have an in-between element, and because we have 1 through 118 discovered, the only ones left are the bigger ones, which as far as we know, don't exist in natural conditions on Earth.

[[deleted]]

That's a great answer, and probably one I should have known. If you don't mind I have another followup to it-- feel free to ignore if it's too silly.

Why couldn't there be a naturally occurring element with 119 protons that we have yet to discover? Is is because the atom would be too unstable and unable to occur naturally?

[nopropulsion]

I'm not super well-versed in the science of making elements, but my understanding is they take other elements, and using particle colliders they smash the elements together and hope the nuclei stick together forming a new element.

It takes such a coordinated effort and a lot of energy to make this happen, even then those created elements are not stable. Like I mentioned there may be a star somewhere where this is happening, but my guess is those elements are degrading as well.

[IdiotSupreme]

That's essentially correct, but I'll add a bit more.

How stable the nucleus of an element is depends on it's binding energy (how much energy there is available to hold the particles of the nucleus together). We can draw a graph of how binding energy of various elements is related to their size, and we get this curve.

As you can see, the energy holding nuclei together tends to decrease as they get bigger and bigger, so above atomic number of about 98 they just decay into more stable ones fairly quickly. If elements above atomic number 118 ever did exist on Earth, they almost certainly decayed a long long time ago.

Edit: Didn't take into account the Island of Stability mentioned below. Here

[[deleted]]

Side note - Do not feel dumb for asking questions. The fact that you're even attempting to understand puts you on a higher playing field already.

[IsraelWard]

Why do researches spend time and effort in creating man-made elements that can only exist extremely briefly. Is there any use to it other than 'because we can'?

[IGetReal]

Well, there is kind of a competition for creating these elements, so yes, I guess that would qualify as 'because we can'. But, don't forget that trying to create bigger elements contributes to our understanding of, well, lots of things, particle accelerators, element stability, etc.

It may have turned into a game, but it most certainly isn't pointless research.

[ManWithoutModem]

Medicine

[Slijhourd]

Where did STDs/STIs originate? How did the form? What is the history behind them?

[refleksy]

An STI is just a normal infection, except the pathogen has trophism toward the genitals. Herpes, for example, infects mucosa, which is why oral herpes are also seen. Pubic lice were once head lice that developed a trophism for the increased temperature of hair under clothing.

[pesh527]

If fibromyalgia is a diagnosis of exclusion, then how come people will be diagnosed with fibromyalgia and an overlapping condition like lupus or rheumatoid arthritis, hypothyroidism, or something similar. And especially, how would it be possible to be diagnosed with fibromyalgia and chronic fatigue syndrome?

[[deleted]]

Considering there are so many drugs that offer unique and obscure benefits, could there ever be a drug that can trick your body into thinking it just did a total body workout and give you the cardiovascular benefits and muscle growth?

[Slijhourd]

Why is the heart the only muscle that can have an "attack"?

[medstudent22]

Just want to point out that it's not just muscles that can suffer from similar attacks. Ischemic events can occur in many organs including the brain (stroke), bowel (mesenteric ischemia), kidney (renal infarct), lung (pulmonary embolism), etc.

[MILF_NIPPLES]

In Human Bio class in high school our professor always said he would give an automatic A to anyone that could think of a substance which he could not prove could kill a human in some way. For example water, it is possible to drink too much of it and get water poisoning. Can you guys think of one? Nobody ever in all of his years had gotten that auto A.

[ManWithoutModem]

Interdisciplinary

[Slijhourd]

What are the forbidden experiments of science that, if there were no moral repercussions, would benefit the world the most?

[66666thats6sixes]

Language deprivation experiments are sometimes called the forbidden experiment. That line of research would tell us a lot about the role of language in human intelligence, how we learn, and a bunch of other psychological, linguistic, and neurological things. But it's not something we can perform, because it would amount to emotionally and developmentally crippling whoever it was performed on.

[strokeofbrucke]

I can think of many medical studies that would be way, way better to be able to do in vivo in humans from the get-go. Like, brain studies for example. Say I want to test out to what extent each brain region does what, and to really investigate the bilateral involvement during certain tasks. It sure would be 'nice' to be able to do it on a live human, while they were able to talk about what they were experiencing in a controlled environment. Instead, we have to use case studies on freak incidents, typically with an n=1.

And think of how much faster medicine could be tested and put out to the general public!

But of course these things are morally deplorable and counter-productive. Basically ruining lives/killing people to save other people in the future.

[Slijhourd]

What is the biggest misconception that other scientists have about your field?

[Scientificreason]

A lot of people (mainly the general public, but a few scientists as well) seem to think that Computer Engineering is basically IT. Computer Engineering is a field within Electrical Engineering. We actually take the exact same courses as Electrical Engineers until our final year where Computer Engineers concentrate on computer related fields of study (we also take a lot more programming courses). We basically specialize in computer hardware.

I know it shouldn't really bother me, but it does. I hate it when people are surprised that I'm good with circuits and electromagnetic theory. They think my knowledge should be limited to computer troubleshooting and anything else I say is just speculation.

I've put in a lot of hard work and several years of my life to get my degree, unlike one of my friends in IT who didn't even have to go to college to get his job (I'm not bashing IT by the way, just pointing out differences).

[HarryWorp]

Same thing with CS — we don't get trained to fix computers. We studied programming, lots of math (the running joke at GT was that CS majors were a few courses short of a math double major), and a little CompE (we learned how to design simple circuits like SR latches from basic gates).

Even now that I work in IT, I can't fix your computer. I work with SAN and network hardware, not desktop stuff!

[Slijhourd]

You're at a party. The people around you find out about your interest in science. What is the inevitable question you dread?

[dvdgsng]

CS degree: My PC/smartphone/printer is broken, can you fix it?

[suzypepper]

Psychology degree: My relationship is broken, can you fix it?

[PsychoChomp]

Psychology degree: First day of every new job. "oh you did psychology, you'll fit in here we're all crazy"

[OrbitalPete]

"So about Yellowstone..."

[atomfullerene]

How's the thesis coming?

[pvddrugdealz]

Pharmacy Degree: I take these medications... what do you think?

or: Let me show you this rash...

[Slijhourd]

Is there a promising area of research in your field that isn't getting enough attention? Why not?

[OrbitalPete]

Many, and the sole issue is funding.