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Sunday, August 14, 2016

When describing an amount of space, we call it an "area" or "volume." When describing an amount of time, we call it a "duration." What would we call an amount of spacetime, and what would that imply?

When describing an amount of space, we call it an "area" or "volume." When describing an amount of time, we call it a "duration." What would we call an amount of spacetime, and what would that imply?

When describing an amount of space, we call it an "area" or "volume." When describing an amount of time, we call it a "duration." What would we call an amount of spacetime, and what would that imply?

Posted: 14 Aug 2016 01:20 AM PDT

Does Einstein's theory of relativity connect electric and magnetic fields?

Posted: 14 Aug 2016 01:37 AM PDT

How were they able to train the brain to recover from paralysis using VR?

Posted: 13 Aug 2016 07:43 AM PDT

I was blown away by this article over on /r/virtualreality.

It looks like a team from Duke were able to train subjects with paralysis using VR headsets each day to slowly allow them to recover some(?) movement/sensation.

Even if it was a small amount it is stil really impressive, but what I don't understand is "how" this works?

Does this only work for certain types of paralysis? (i.e. if the spinal cord is severed surely there is no chance of any repair without surgery/physical treatment?)

If this works, could it be rolled out without the need for a treatment team? i.e. an app + headset would allow anyone who fits the criteria to benefit?

(This is my first reddit post so be gentle)

submitted by /u/WozzyWozniak
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How Much Information can the Observable Universe Contain?

Posted: 14 Aug 2016 02:57 AM PDT

If we interpret the observable universe as some kind of data-storage operating at the smallest scale possible, how much information could it theoretically be able to store, assuming that we have infinitely much energy at our disposal to express information?

Edit: English

submitted by /u/QuirkyUsername123
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What is in the surface ice of Ganymede?

Posted: 14 Aug 2016 04:33 AM PDT

How does the ice react to the intense temperature changes?

submitted by /u/jaredwebd
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How durable could a razor blade be made?

Posted: 13 Aug 2016 01:45 PM PDT

The web is rife with stories of how the metal (I presume it is steel) used for most commercial razor blades is designed with planned obsolescence in mind, with the intent of selling as many blades as possible to consumers. I have the following questions:

1 - is this "common wisdom" demonstrably true?

2 - If so, how durable could a common razor blade be made if one ditched the philosophy of planned obsolescence and aimed for maximum durability instead? What kind of metal would be best adapted to produce durable blades which remain sharp and effective as long as possible, and what would it's composition and properties be?

submitted by /u/Gargatua13013
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If Earth had rings like Saturn would the night time be significantly brighter due to reflection from the Sun?

Posted: 13 Aug 2016 02:41 PM PDT

I just read this post on /r/interestingasfuck and seeing the ring so bright over Washington made me question if the rings would light the Earth like the light from a full moon does.

It probably depends on the distance the debris in the ring are from Earth, so assume the ratio of Saturn's rings from its surface are the same in this scenario.

Would the Earth be lit significantly brighter by the reflected light at night? Or are the rings too close to the surface to catch the light of the Sun at night?

Also bonus question, would there be a noticeable shadow on the surface from the rings? Or would the light be diffused enough over the distance so that no shadows are able to be defined?

Thanks.

submitted by /u/dublzz
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Why does an egg become solid when heated up?

Posted: 14 Aug 2016 08:00 AM PDT

If everything becomes a liquid then a gas when it gets heated enough then why does an egg become solid when cooked? No other food that comes in my mind does that.

submitted by /u/Yuberee
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How does temperature-dependent sex determination work? Wouldn't the embryos already contain XY/XX chromosomes?

Posted: 13 Aug 2016 03:14 PM PDT

In some species, such as amniotic reptiles such as the alligator species, temperature plays a key role in determining the sex of the offspring. How does this phenomenon work? Surely the developing animals already have the genetic material needed to decide their sexes?

submitted by /u/Viewbob-True
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Is it a coincidence that the first four planets nearest to the sun are all much smaller then the four other planets?

Posted: 13 Aug 2016 01:40 PM PDT

What are the differences between interstellar space and intergalactic space?

Posted: 13 Aug 2016 04:25 PM PDT

If dark energy is popping into existence in intergalactic space and causing the accelerating expansion of the universe, why doesn't this happen in interstellar space within galaxies?

submitted by /u/commander-crook
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How does one measure sudden deceleration, such as with a vehicle hitting a wall? At what precise point or event does the beginning of the deceleration period begin and when does it effectively end?

Posted: 13 Aug 2016 07:10 AM PDT

I saw another post about some race car having undergone about 200g of deceleration when it slowed from ~100mph to 0 in 2 seconds. It seems like the deceleration itself would even have some variation to it over time, as leading material crumpled and slowed the following material.

submitted by /u/star_boy2005
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Are there applications of action principles and Noether's theorem outside of fundamental physics?

Posted: 13 Aug 2016 09:42 AM PDT

Has anyone run across the use of action principles and Noether's theorem as mathematical modeling tools outside of fundamental physics? Perhaps in areas like engineering, biology or even economics?

submitted by /u/RiggedHilbert
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How does fluid loss affect cognitive ability?

Posted: 13 Aug 2016 06:01 AM PDT

Earlier, I saw this TIL in /r/formula1:

Sports studies have underlined the importance of fluid level in the body. A person who has lost 4% of body weight can lose up to 40% of their psycho-physical ability.

However I can't find a source that shows this 40% figure, and I only found a single study that talks about cognitive ability loss after dehydration. Anyone here knows more?

submitted by /u/MyWholeTeamsDead
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If friction is independent of area of contact, why do cars with wider tires have more traction?

Posted: 13 Aug 2016 06:55 PM PDT

How is the Riemann Hypothesis related to prime number distribution?

Posted: 12 Aug 2016 11:34 PM PDT

Whenever I hear about the Riemann Hypothesis I hear it is related to prime number distribution. But how is it so?

Thanks!

P.S.: Numberphile fan here!

submitted by /u/fgiancarelli
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How is water pressure generated by a distribution company? How is pressure is increased to individual fixtures?

Posted: 13 Aug 2016 04:33 AM PDT

Since the water to comes out in higher pressure when the faucet is loosened, this means there is an excess of water pressure that is being resisted by the individual valves.

1) What do companies do to increase pressure 2) If it relies on an elevated reservoir, why doesnt the pressure decrease when multiple valves are open 3) How is the pressure increased with individual fixtures like showers, bidets etc.

submitted by /u/khlumps
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Saturday, August 13, 2016

How do two interfering EM waves conserve energy in all cases?

How do two interfering EM waves conserve energy in all cases?

How do two interfering EM waves conserve energy in all cases?

Posted: 13 Aug 2016 01:35 AM PDT

Intro below, question in bold at the bottom.

Hey guys! I'm a molecular electronics PhD student at Leiden university, and before that did a nanoscience MSc at Groningen university. I've asked this question to my fellow students and also some postdocs and professors. We have not yet found a satisfactory answer.

The problem is a gedankenexperiment where two laser beams or more specifically: two electromagnetic waves meet each other and interfere perfectly destructively or constructively. So we have two (for example) laser beams that cross paths. Now, each laser sends out an oscillating electromagnetic field with a certain power (say 100 watts). We set up the system in such a way that they interfere constructively completely. When the two beams cross and in, we can add the beams vectorially and end up with an EM-field with twice the amplitude. Since the energy density of an EM-field goes with the amplitude squared, we suddenly have four times the output power.

Now, I know that this cannot be. We could simply use quantum mechanics and say: well, we just have twice the amount of photons now, and photons do not interfere with each-other, only with themselves. Therefore, you just have twice the power, not four times. However, this answer sounds unsatisfactory to me. I think that the answer should be simpler and should not require quantum mechanics, or anything other than the laws of Maxwell.

Furthermore, I'm not interested in answers along the lines of: "Well, you can never make a laser like that, since the laser linewidth is never infinitely sharp". I think that the solution should not be practical one, but a principle one.

I have looked at this thread. However, the answers here are among the lines of: well, the intensity goes somewhere else. So that means that whatever interferes destructively somewhere, should interfere constructively somewhere else. This sounds like the most valid answer, but I don't see how this is a fundamental and not a practical issue.

For example: we could take a laser beam with a width of half the wavelength (I now this is not practical, but I don't see why we cannot do this fundamentally), and at 90 degrees cross another identical laser beam, so that they interfere constructively. Twice the field amplitude, four times the power. We could also interfere destructively and end up with no power.

So my question is: how do we solve this problem? And if it has to do with constructive interference in one place, destructive interference in the other, why should this not depend on the geometry if the setup, eg. the width and angle of the two beams?

submitted by /u/Blokshibe
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How do dung beetles extract nutrients from waste product?

Posted: 12 Aug 2016 07:59 PM PDT

Is there any meaning to rotation around the time axis in spacetime?

Posted: 12 Aug 2016 04:30 PM PDT

If spacetime is a four-dimensional object, and you can rotate around the three spatial axes, how would you interpret rotation around the time axis?

submitted by /u/ergotist
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Why are electric fields additive?

Posted: 13 Aug 2016 07:49 AM PDT

In undergraduate physics, you are taught that if you add the individual forces that a set of electrically charged particles put on another, that sum will be equal to the force experienced by the particle.

But let's say you have 3 particles in a line. Apparently this rule still holds. However, forces are supposed to be carried by particles in QM, the photon specifically here. If you shine a light, which is made of photons, on two inline objects, it won't hit the farther back one, because that is in shadow.

So if electric force is additive for inline particles, that makes it sound like the photons from the far left reach the particle on the far right, when the shadow example makes me think it shouldn't. How does that work?

submitted by /u/Bananawamajama
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A photons wavelegth increases because of cosmic expansion. Does the same happen to the (De Broglie) wavelegth of matter-wavefuntions? Does this mean all matter, not only photons, lose energy/momentum?

Posted: 12 Aug 2016 05:42 PM PDT

Is it feasible to completely eradicate mosquitoes without devastating the ecosystem?

Posted: 12 Aug 2016 09:22 AM PDT

Is there a research-backed process to create a healthier gut biome, particularly for achieving a healthy weight?

Posted: 12 Aug 2016 02:15 PM PDT

I've read about an individual receiving a fecal transplant and becoming obese because the donor was overweight. Given the obesity epidemic, has there been a recommended diet that helps create a gut biome that actually helps achieve a healthy weight?

submitted by /u/cisco55
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Why do the bubbles in Latte foam periodically pop in waves?

Posted: 12 Aug 2016 12:59 PM PDT

Here I am doing science at my desk and I find myself periodically distracted by the (very quiet) sound of the foam in my latte popping. Desperate for any distraction, I investigated.

Periodically (every 2-3 minutes) the popping sounds get louder for a second and then die back down. It's these periods of higher intensity that distracted me (not that it's hard to). I observed the foam for a bit and realised that the increased intensity coincided with a 'wave' of bubbles popping.

I set up a makeshift camera stand by stacking two cans of soda and recorded the effect with my phone: https://youtu.be/57ZlEtC5iAU (wave starts near the south-east of the mug, near where the white foam touches the wall of the mug).

What causes these periodic waves to occur? Intuitively I would have thought that the timing of the bubbles popping would be stochastic enough to avoid these sorts of effect, but I can see that if there are a sufficient number of 'about to pop' bubbles that a wave could be started.

Some (interesting?) observations:

  • The wave starts from the same are of the cup each time
  • The wave travels around the streak of white foam in the center, never through the white foam (as far as I can tell)
  • If I take a sip the effect is accelerated (happens only a few seconds after a sip consistently)
  • If I wiggle the mug just enough to cause small waves in the liquid but not enough to make the foam move from where it's attached to the side of the mug, the timing of the waves seems to be unaffected

Some off the cuff questions:

  • Since the wave tends to start in the same place, and in this case the wave starts near a patch of white foam, does the 'type' of foam affect the wave? It seems to since the wave goes around the white foam.
  • Do other 'foamy' systems exhibit this behaviour (beer, bubble tea, sea foam, etc.)?

Thanks for any insight :D

submitted by /u/jmct
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Why does an alternator turn slower, or resist turning more when under load?

Posted: 12 Aug 2016 01:51 PM PDT

I noticed this in my car when I would activate something that draws electricity like window motors, the engine RPMs would drop slightly until I let off the window motor button. Is this a stupid question and I'm totally wrong about what's actually happening to cause the engine RPMs to dip while there's an electrical load? Thank you for any useful input!!

submitted by /u/knivesngunz
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Why do fish when they die artificially float to the top of the water, but don't appear to in any other case?

Posted: 12 Aug 2016 11:11 AM PDT

Why does it seem like when fish die artificially (be it from the lack of oxygen due to thick ice or eutrophication, or some poisonous substances) they almost always float to the top of the water, but when they die in any other way(from old age, if that is even possible, or from disease) they don't float to the top?

submitted by /u/fjellhus
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Is listening to relaxing meditative music during study a help or a hindrance?

Posted: 12 Aug 2016 09:49 AM PDT

I've heard two schools of thought on this:

(1) It helps focus attention, bully out distracting thoughts from the mind and create a sense of relaxation to calm the anxiety of impending exams.

(2) You should study in exam conditions so that you don't need a certain external stimulus such as a chair, sound or smell to trigger off the memories in your mind.

Obviously, whatever works for the individual is best but I was wondering if there is a scientific consensus on the topic.

submitted by /u/VeterinaryStudentK9
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What are the technical differences between amylose and cellulose and can we turn one form to another?

Posted: 12 Aug 2016 02:16 PM PDT

They're both built with D-glucose units, however one is wood, and the other is bread. Why do they differ so much?

We throw away alot of paper, cardboard etc. Is there any industrial process that we could say recycle cellulose? turn it into amylose for animal feed? perhaps even decompose it into glucose for use in making bio-fuel?

submitted by /u/aortm
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How many satellites is needed for locating via GPS?

Posted: 12 Aug 2016 03:09 PM PDT

And why is more better? Is it only because of more possibilities to get right data?

submitted by /u/Dokans
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How does the pressure at the lowest point of the Mariana Trench compare to the pressure in space?

Posted: 12 Aug 2016 04:45 PM PDT

Can the barycenter of a two-body system be a Lagrange point?

Posted: 12 Aug 2016 07:26 AM PDT

First let me say that I'm a total novice, so I may be using these terms incorrectly, and I definitely have no grounding in the mathematics that describe these sorts of scenarios. Let me clarify what I mean: Barycenter: the center of mass of a system of celestial bodies, and therefore (if I'm interpreting Kepler's laws correctly) one of the foci in all elliptical orbits in the system. Lagrange Point: a gravitationally neutral point in a system that may or may not move based on the constituent orbits in the system. If these definitions are wrong, please tell me. But insofar as the underlying wrongness does not disallow my question being compatible with reality, I would love to learn more in this area.

submitted by /u/139mod70
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What are some intuitive applications of eigenvalues/eigenvectors in engineering?

Posted: 12 Aug 2016 08:34 AM PDT

I somewhat understand the concepts, but I have a hard time understanding how they are applied or what they represent in the physical world, so some examples would really help me.

submitted by /u/Rimio
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How does a neutrino detector work?

Posted: 12 Aug 2016 10:18 AM PDT

Could the "bionic leaf" technology be used to trap or convert CO2 on a large scale in a way that would help reduce (and hopefully reverse) the effects of CO2 emissions on the environment?

Posted: 12 Aug 2016 08:26 AM PDT

I just saw an article on utilizing a bionic leaf that can collect CO2 in the air to use as fuel. Could the same technology be used to trap or convert CO2 on a large scale in a way that would help reduce (and hopefully reverse) the effects of CO2 emissions on the environment?

submitted by /u/GandalfTheWhey
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How much pressure is needed to compress water?

Posted: 12 Aug 2016 09:10 AM PDT

Solids are compressible to the extent with enough force you could lessen the amount of space a solid occupies, is this also possible with water?

submitted by /u/shercroft
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What's something considered basic/common, that we still have little to no understanding of?

Posted: 12 Aug 2016 12:47 PM PDT
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Friday, August 12, 2016

If the universe is an hypertorus, is it possible that we receive the light from a star twice ?

If the universe is an hypertorus, is it possible that we receive the light from a star twice ?

If the universe is an hypertorus, is it possible that we receive the light from a star twice ?

Posted: 12 Aug 2016 06:22 AM PDT

I recently read an article in a French science magazine stating that the universe might be an hypertorus (Euclidian, finite and borderless). They represented it using a cube in which when you exit through one side you actually come back in from the opposite one.

I made a drawing to make my question clearer : Drawing

The three panels on the left represent the universe in 2D and when you move through a side you come back through the opposite one. The star is any star and the black dot represents the Earth. The arrow is the light emited from the star.

The three right panels represent what we see from the surface of the Earth.

  • The first 2 pictures are straight-forward the star lits us directly and we see it in the sky as it was at the moment the light was emited

  • On the second line of the "comic" you can see the light traveling through the right side and coming back out of the left one and then hitting us. What we then see in the sky is a second star that appears to be way further than the first one and way older, when it is in fact the same one !

  • On the third line I was imagining a scenario where the light goes through the loop several times. We would then see the star as it was a very long time ago, or even maybe witness it's birth ?

To recap

It sounds crazy but would it be possible that we see the same star at different moments of it's life span ?

submitted by /u/Smarterthanstuff
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Could CRISPR eventually allow us to borrow genes for limb regrowth from things like lizards?

Posted: 11 Aug 2016 07:07 PM PDT

How does Newton's Law of Gravity help us predict the orbits of the planets with "great accuracy"? (Please read description.)

Posted: 12 Aug 2016 03:29 AM PDT

I'm reading A Brief History of Time by Stephen Hawking. On pg. 17, there is a paragraph that reads:

 

"Newton's law of gravity also tells us that the farther apart the bodies, the smaller the force. Newton's law of gravity says that the gravitational attraction of a star is exactly one quarter that of a similar star at half the distance. This law predicts the orbits of the earth, the moon, and the planets with great accuracy. If the law were that the gravitational attraction of a star went down faster with distance, the orbits of the planets would not be elliptical, they would spiral in to the sun. If it went down slower, the gravitational forces from the distant stars would dominate over that from the earth."

 

What does the part in bold mean exactly? (As is clear, I'm a layperson, so please keep it simple.) Thank you!

submitted by /u/InterstellarBlue
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Is there a relation between how tree branches/roots grow and how our own bodies creates its cardiovascular system?

Posted: 12 Aug 2016 05:39 AM PDT

What do we currently know about possible safety factors used for the construction of ancient structures as well as the margins for material failure ancient civilizations may have been aware of?

Posted: 11 Aug 2016 07:10 PM PDT

For example, did they have a kind of crude knowledge of Poisson's ratio or Hooke's Law even without calculus? Was it literally just trial and error? It seems plausible that they would have had some knowledge of material science since civil engineering is the oldest form of engineering in the world.

submitted by /u/SomewhatRandom108
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Does the sun experience tides?

Posted: 11 Aug 2016 06:32 PM PDT

Does the sun experience forces of gravity from its orbiting planets significant enough to have measurable or theoretical fluctuations in matter height? If so, is there an accepted value for tidal height?

submitted by /u/JoeRmusiceater
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Why a spacecraft reentry has to be so violent? Why don't they make reentries at slower speeds to avoid all the heating up and stuff?

Posted: 11 Aug 2016 10:26 PM PDT

What is the current State of the art in human imaging

Posted: 11 Aug 2016 07:58 PM PDT

I was wondering what imaging techniques (or combination of imaging techniques) are currently pushing the envelope when it comes to imaging the human body in vivo with high resolution and signal sensitivity.

submitted by /u/alphaMHC
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How much worse could The Chernobyl Disaster have been?

Posted: 11 Aug 2016 02:19 PM PDT

What is the observed frequency-size distribution of Bolide impacts, and can this be extrapolated to predict the frequency of Tunguska-like events?

Posted: 11 Aug 2016 06:19 PM PDT

Maybe bolide isn't the right word.

submitted by /u/iorgfeflkd
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Why are patients with concussions told not to sleep, or not to sleep for long periods?

Posted: 11 Aug 2016 11:50 AM PDT

Are there any formulas for predicting properties of alloys?

Posted: 11 Aug 2016 06:55 PM PDT

How is a bank account pincode not easily hackable when the small authenticator we use for online payments can verify my pincode without needing any sort of connection to a server or other online service?

Posted: 11 Aug 2016 12:34 PM PDT

I tried finding out via Google but didn't find a good way to describe the question to receive good results. The authenticator we use can recognize the pincode of any bank account of the bank in question that produced the authenticator. It doesn't seem like a sophisticated piece of hardware (being small, light and handed out for free by banks). How can it do this without the data inside being easily hackable?

submitted by /u/Jeissenberg
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Why does it take so long for radioactive material to decay?

Posted: 11 Aug 2016 01:30 PM PDT

To what extent do molecules of similar shape share the same properties?

Posted: 11 Aug 2016 02:44 PM PDT

I was watching a documentary on drugs and they states that Adderall and methamphetamines share similar properties due to their similar molecular shape. However, in my organic chemistry class, I learned that adding a lone functional group to a molecule can alter its function entirely. Thus, to what extent do molecules of similar shape share the same properties?

submitted by /u/Jellio
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With scientists recently discovering the 400yr lifespan of the modern Greenland shark, are there any new insights into its prehistoric counterparts?

Posted: 11 Aug 2016 08:34 PM PDT

Article

After googling & wikiing past the article a little bit, it appears there's been some speculation over time as to whether or not very large prehistoric animals relied on some kind of warm-blooded adaptation. Does the new discovery of the persistence of the Greenland shark offer any new or interesting biological comparisons to its great ancestors? It sounds like the concept of "the lifespan of dinosaurs" is still speculative in general. So a better question may be whether the Greenland shark (tissue?) can provide any insights into the mechanics of metabolism in general.

Thank you!

submitted by /u/saucedog
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How do peas know where to climb?

Posted: 12 Aug 2016 12:19 AM PDT

[neuroscience] What is the brain doing when a person is in a coma?

Posted: 11 Aug 2016 10:22 AM PDT

Electrically to be specific

submitted by /u/ToThyneOwnSelfBeTrue
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Can a meteorite be struck by lightening?

Posted: 11 Aug 2016 06:02 PM PDT

What would the factors be?

submitted by /u/graceful_fox
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Will there ever be a cure for Alzheimer's? If so, how long away is it?

Posted: 11 Aug 2016 07:59 PM PDT

Obviously no one knows, but what is the general consensus among the medical community?

I'm an 18 yr old with a family history of Dementia/Alzheimer's, and I'm curious if we're likely to make any big strides towards better treatment before my possible onset.

submitted by /u/TurquoiseCorner
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