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Sunday, November 27, 2016

What is the difference between the local and global speed of light?

What is the difference between the local and global speed of light?

What is the difference between the local and global speed of light?

Posted: 27 Nov 2016 04:28 AM PST

As explained here you'll always measure the same value for c locally, but globally it might be lower because of gravitational fields. What I'm wondering is at what distance do you consider something to be global rather than local?

That might be a plain misunderstanding from my part, so alternatively, is it more correct that the local measurment is just an approximation of the global one, since we don't expect any significant space-time curvature in proximity of the measurment (and therefore, the measurment is actually a tiny bit inaccurate)?

submitted by /u/MightyLordSauron
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Is length contraction an optical illusion or physically real?

Posted: 27 Nov 2016 12:04 AM PST

In the Veritasium / MinutePhysics video How Special Relativity Makes Magnets Work, the explanation is that length contraction has a real physical effect. The protons become length contracted, made denser, and therefore produce a positive electric field, which repels the positively charged cat.

But... in some edge cases, it seems like this explanation would also predict some very bizarre behavior.

Let's say there's a gas cloud on the verge of becoming a star, or a star on the verge of becoming a black hole. Then let's say I start traveling at near the speed of light. From my perspective, the rest of the universe will appear length contracted. But... the video seems to say that this contraction isn't just some optical illusion, that things are really physically contracted, which can have real physical effects such as the density of charges. But if that's the case, wouldn't the almost-a-star gas cloud, or the almost-a-black-hole star, be denser? ...But only from my perspective?

submitted by /u/MoTTs_
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Why does my throat hurt when I scream or yell for long periods of time?

Posted: 26 Nov 2016 07:36 PM PST

Approximately how big was the sun when it was a planetary nebula?

Posted: 26 Nov 2016 06:01 PM PST

Can someone explain why this happens? (Link in text)

Posted: 27 Nov 2016 05:40 AM PST

In the linked video, an astronaut says that the brain shuts down the vestibular system and relies more on information that is coming from the eyes for balance coordination in microgravity. How come the brain evolved to adapt to such situations which are relatively new to the humans?

Posted: 26 Nov 2016 02:19 PM PST

Video. Are there any situations on earth where the brain has to rely on the information coming to the eyes for balance coordination? Probably this could happen if the vestibular system is damaged but in the case of astronauts the brain still switch to the eyes for balance with a healthy vestibular system.

submitted by /u/333ml
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Is there a limit on how exact weather predictions can get?

Posted: 26 Nov 2016 07:13 PM PST

I know there is some serious math and use of statistics involved and that it is under constant research.

Also, i know you can't achieve 100% accuracy for a distant future (because chaos).

But where is the point of what could be done and what couldn't

submitted by /u/cebrito
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[Physics] Why does the speed of light change with altitude?

Posted: 27 Nov 2016 06:43 AM PST

[Physics] Looking at this page here it looks that is correct. I have been wondering why.

I am thinking its to do with air pressure or to the density of the air or something.

And does the speed of LIGHT change too the closer to earth it gets?

submitted by /u/GooseNZ
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If elements are formed by atomic fusion within stars essentially at random, with some elements being more likely to arise than others, why is it that elements of a kind are always found together with more of that element?

Posted: 26 Nov 2016 03:31 PM PST

I could also have flaired this as planetary science or Earth science, but figured astronomy might be closest to the best category

submitted by /u/non-troll_account
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Why couldn't a submarine sent to Titan tap into the methane seas for the energy to explore it endlessly?

Posted: 26 Nov 2016 01:21 PM PST

In the double slit experiment, how far can you push reverse causality?

Posted: 26 Nov 2016 10:11 AM PST

I've known about the weirdness that the double slit experiment reveals for a while, but just today (reading the excellent science fiction novel The Flickermen) found out about reverse causality.

Doing research online, it seems this is scientific fact. When you do the double slit experiment using detectors to measure the stream of photons, that collapses the waveform and instead of the wave pattern, you see two lines. However, if the data from the detectors is erased, the wave pattern is seen, even though the measurement actually occurred.

This is my understanding so far.

Here's the question. What would happen if you look at the screen before looking at the data and then, while looking, someone deletes the detector data? Would the wave pattern return?

This is where I believe the novel departs from reality and my guess is once you've seen either side of the results - either the data or the pattern the waveform has collapsed and nothing will bring it back, but obviously, in quantum mechanics guessing and logic seem don't seem to play a big part...

I'm especially interested in hearing from people who've actually seen this experiment in the lab.

submitted by /u/f_leaver
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What does color mixing look like in terms of math?

Posted: 26 Nov 2016 09:10 AM PST

While working with photoshop I noticed a blend tool that could blend colors together, and then I realized that I'm not sure how it knows. Is there a mathematically process to color mixing using RGB, Hex, and/or CMYK? If so, what does it look like?

submitted by /u/Lilgherkin
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Saturday, November 26, 2016

If you point your phone camera at an IR LED (like in a TV remote) it is visible but why does it show up as blue/purple rather than red?

If you point your phone camera at an IR LED (like in a TV remote) it is visible but why does it show up as blue/purple rather than red?

If you point your phone camera at an IR LED (like in a TV remote) it is visible but why does it show up as blue/purple rather than red?

Posted: 25 Nov 2016 09:54 AM PST

Where does the kinetic energy go here?

Posted: 26 Nov 2016 06:25 AM PST

Imagine you and your buddy Neil Armstrong are in space. You both see a bunch of objects of different sizes and at different distances moving towards your direction, all of them around the same speed. From your frame you calculate the kinetic energy of all this particles.

Then Neil pushes you while grabbing the spaceship, giving you the same speed and direction as this particles. From your new frame of reference all this stuff is standing still. The kinetic energy you can measure now is from the spaceship and from Neil which is less than the original.

What happened with the energy? Where does it go? Or is energy relative?

...You then remember Neil has just double-crossed you and curse him at the top of your lounges while you descend into deep space

submitted by /u/clumsywatch
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What is the brigthest planet as seen from another planet?

Posted: 26 Nov 2016 03:14 AM PST

I know that venus is the brigthest planet as seen from earth, but aside from the Sun and moons, can more brigth celestial objects be seen from other planets?

I know few things that come into account when calculating this

-Planets distance from the sun

-Distance of planets between each other

-Size of the planet

-Reflectivesness of the planet

-Possible relative allingments of the 2 planets and the Sun

But its way above me to put all of them together.

submitted by /u/empire314
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Why do tires on cars when doing a burnout give white smoke, but a pile of tires burns black?

Posted: 26 Nov 2016 04:47 AM PST

When a pair matter-antimatter is formed, why does it annihillates itself instead of just sticking together?

Posted: 26 Nov 2016 06:05 AM PST

Why are most all of the world's deserts sandy?

Posted: 25 Nov 2016 09:25 PM PST

Obviously when things like all of Antarctica are classified as a desert, not every single one is covered in sand. But I'm curious as to why this seems to be the case - or if this is even the case at all.

submitted by /u/LetterToMySO
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Do 15 year old dogs get cancer at rates similar to 15 year old humans, or to humans at a similar point on their lifespan?

Posted: 26 Nov 2016 07:12 AM PST

How can we differentiate so many simultaneous sounds?

Posted: 26 Nov 2016 07:11 AM PST

So I understand that sound waves are vibrations in a medium; for example, a drum sends a wave of energy through the air that eventually vibrates the air molecules next to my ear drum, which is then translated into a recognisable sound by my brain, as opposed to actual air molecules next to the drum being moved all the way over to me. But if I'm listening to a band and all the instruments are vibrating that same extremely limited number of air molecules inside my ear canal, how is it that I can differentiate which sound is which?

submitted by /u/duetschlandftw
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What property of a charged particle causes the charge?

Posted: 26 Nov 2016 06:54 AM PST

In other words, what is charge? What causes us to say; "Well okay, an electron has a negative charge and a proton a positive charge."

submitted by /u/imRobert7
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Why do some species have such enormous individual variation while others look pretty much all the same?

Posted: 26 Nov 2016 06:01 AM PST

Common Buzzards Buteo buteo for example have huge difference in colouring despite being the same species and subspecies, and there being no apparent geographic component to the variation. Two Buzzards in the same field can look so different a layperson wouldn't even think they're the same species. Yellow Wagtails Montacilla flava are known for having a large number of subspecies which all look different but are still considered the same species, here you can see that the different subspecies come from different places, indicating that the variation is a result of geographic distribution differences. In many cases it is possible to differentiate between a Yellow Wagtail from the Iberian peninsula from one from Italy from one from Sweden, for example, based on the way it looks alone. Osprey Pandion haliaetus however is one of the most widespread bird species in the world, but one from North America looks pretty much identical to one from Europe. What gives?

submitted by /u/YoSoyUnPayaso
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What would happen if someone was placed inside a giant hollow cube with gravity being exerted uniformly by all 6 walls?

Posted: 26 Nov 2016 05:21 AM PST

Would the uniform gravity from all sides of the cube cancel out and result in zero-gravity? Assuming that the experimenter is placed at the center of the cube, with the pull of gravity being equal from all sides.

submitted by /u/TheFlyingSultan
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[Biology] What makes nucleic acids unique?

Posted: 25 Nov 2016 10:02 PM PST

What makes nucleic acids so different from all other biomolecules? How have they evolved so differently from the rest of the biomolecules?

submitted by /u/Artappa
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Why does our tiny lump of rock that is Earth have so many different elements?

Posted: 26 Nov 2016 07:15 AM PST

It seems so unlikely, that our planet, which in the grand scale of the Universe is so tiny, that there is some of every single known element present. Surely it would be much more likely for a planet to consist of a few core elements? Does our variety of elements say anything about how our planet may have formed?

submitted by /u/sim_sayer
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Why do our pupils dilate when we get concussions?

Posted: 26 Nov 2016 07:11 AM PST

Is it evolutionary to let us know we have a concussion or is it a true symptom?

submitted by /u/XGX787
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Is there any chance the Large Hadron Collider (LHC) poses any threat to the scientists who work with it, or at all to other humans and animals?

Posted: 25 Nov 2016 07:32 PM PST

With the Large Hadron Collider being a powerful particle accelerator, is there any evidence of the scientists working on it suffering from any cancers or the like?

Could those atoms being accelerated veer off course and escape from the LHC?

submitted by /u/SpartanOfThePast
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Why do some smells (garlic, smoke, etc.) "stick" to skin/clothes more than others?

Posted: 26 Nov 2016 06:33 AM PST

Why did humans start wearing clothes?

Posted: 26 Nov 2016 05:27 AM PST

So I'm curious as to why humans evolved "out of" their fur and into clothes.

submitted by /u/eprosmith
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Would having a stronger core affect childbirth?

Posted: 26 Nov 2016 05:27 AM PST

Would having great core strength prior to becoming pregnant and then maintaining this strength (somewhat) ease childbirth/make it quicker/easier?

submitted by /u/styrofoam_nun_
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How to calculate Bessel function and its constants?

Posted: 26 Nov 2016 04:23 AM PST

My understanding is the equation y'' + 1/x y' +(m2 - a2 / x2 )y = 0 would have the solution y = C1 J1 (mx) + C2 j2 (mx)

But how to determine the Bessel functions J1, J2 and their corresponding constants C1 and C2?

Thank you!!!!

submitted by /u/mech210
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Do the constellations we see on Earth look the same from Mars?

Posted: 25 Nov 2016 05:15 PM PST

Since Chickenpox is a virus, doesn't stay in your system forever? If so, why don't children of adults who have had the virus immune to it?

Posted: 25 Nov 2016 11:30 PM PST

I'm under the assumption almost everybody eventually get chickenpox, most during their younger years. But if your parents (or even just your mother) have had it, why aren't you immune to it?

EDIT: "why AREN'T children of adults..."

submitted by /u/BambooGamer
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Why do English speakers pick up the accent of other English speakers if they're around them long enough, and does the same thing happen in other languages?

Posted: 25 Nov 2016 10:51 PM PST

Why is it that the range of any given force tends to be inversely proportional to the mass of the particle transmitting it?

Posted: 25 Nov 2016 05:36 PM PST
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Friday, November 25, 2016

How does radio stations transmit the name of the song currently broadcasted?

How does radio stations transmit the name of the song currently broadcasted?

How does radio stations transmit the name of the song currently broadcasted?

Posted: 24 Nov 2016 08:21 AM PST

Just noticed that my car audio system displays the name of the FM radio station, the song being played and its genre. The song/singer name updated when the song changes. How is this being broadcasted? Radio waves can include this information also?

EDIT: Thanks for all the answers! Learnt something new :)

submitted by /u/pfc_homeuser
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If you explain 3^2 as three multiplied by itself twice, how do you explain 3^-1 using the same language convention?

Posted: 24 Nov 2016 07:32 PM PST

E.g 32 = 3 x 3

31 = 3

31 = 1/3

As in, you can explain positive powers by saying the base multiplied by itself x number of times. But how do you explain negative exponents in the same way? Can you even? 3-2 isn't 3 x itself negative 2 times, it's just 1/32.

How do you explain this using language?

Source: A friend asked me this, had no idea.

submitted by /u/juicy_cantaloupe
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How are inertial confinement fusion reactors fueled?

Posted: 25 Nov 2016 03:34 AM PST

I saw this comment from u/tminus7700 in a previous r/askreddit post:

You just shoot the pellets machine gun style into the chamber and fire whatever energy to light them off as they arrive at the focal point.

I tried to research further, but I didn't find anything on Google with the keywords "Inertial confinement fusion machine gun".

If you want to use an inertial confinement reactor efficiently you want a method to refuel it without depressurising the reactor chamber to place the pellet.

Anyone willing to provide further information? Thanks

submitted by /u/Chasar1
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Shouldn't time dilation be symmetric so that earth observers see an astronaut's 'clock' as running slower and vice versa? Why then, would the astronaut come back as younger if the effect is symmetrical?

Posted: 25 Nov 2016 02:49 AM PST

Just learning special relativity for the first time in class, and I don't really get this.

submitted by /u/coolamebe
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Does most oceanic life live close to the coast?

Posted: 24 Nov 2016 10:01 AM PST

What does the distribution of biomass in the ocean look like?

submitted by /u/shoplifter9003
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When does a bullet reach its maximum velocity?

Posted: 24 Nov 2016 03:29 PM PST

I was wasting my time on youtube watching gun videos and this got me thinking. The bullet has to reach Vmax from standstill in some time, then is slows down due to air drag. It should be somewhere in the barrell, but is there a way to know when and where? Also is this related to the force the gun kicks back with?

submitted by /u/Dredddddd
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How can some filters/membranes be permeable to liquid but not permeable to gas who's particles are no where near the MCOW?

Posted: 24 Nov 2016 08:54 AM PST

How do organisms that reproduce offspring asexually determine when to reproduce?

Posted: 24 Nov 2016 02:07 PM PST

With the advancements in technology in recent years, why does it seem that radio signals and the strength of signals have appeared to stay the same?

Posted: 24 Nov 2016 06:51 PM PST

I ask this because when I drive the truck for my work I listen to the radio, but when I get into the city it seems that the strength of the signal weakens and when I go in the tunnels it vanishes. This happens to all but two stations and most of the stations are within 10-25 miles to the city.

Is it cause the city can cause the signals to weaken? Or do other stations using similar frequencies that can cause this to happen? Or is it a combination of things?

submitted by /u/UncleBen94
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Does the heat produced by combustion engines have an effect on Earth's temperature?

Posted: 24 Nov 2016 07:44 PM PST

Over Thanksgiving dinner my father and I were discussing climate change and the topic of heat generation came up. His argument is that since fossil fuels are essentially stored thermal energy, burning them is releasing that energy.

A quick calculation says that all the cars in America produce enough heat each year to raise Lake Michigan's temperature by one degree Fahrenheit. So that energy has to go somewhere.

I think he's missing something since we only hear about the effects of the chemical waste of engines and not the thermal waste.

submitted by /u/PiLamdOd
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Why Radar systems need wide bandwidth? Is it because of the resolution?

Posted: 24 Nov 2016 05:10 PM PST

What chemical reactions are behind DNA replication?

Posted: 24 Nov 2016 05:17 PM PST

So I found this GIF and I was wondering what causes these things to move in an orderly fashion

submitted by /u/notam0derator
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Is the false vacuum theory a common theory in the scientific world ?

Posted: 24 Nov 2016 12:59 PM PST

So today I learned of the existence of this theory, and from what I understood, in a very simple version it basically says that our universe as we perceive it is similar to a bubble and can suddenly burst at any moment, right ? Is this a widespread theory ? If so, what are the things blocking scientists to make advances to prove it, and if not, what are the things that "discredit" it ?

submitted by /u/Kounro
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Is there any substitute to the Hohmann transfer?

Posted: 24 Nov 2016 02:54 PM PST

If there is one, how is it called and how does it work then?

submitted by /u/Wakka2462
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Why doesn't Raoult's Law depend on the chemical nature of solute?

Posted: 24 Nov 2016 11:15 AM PST

According to Raoult's Law, dissolving a solute into a solvent decreases the saturation vapor pressure. Being a colligative property, it doesn't matter what the chemical nature of the solute is, only how much there is.

However we know that things like melting point and saturation vapor pressure (and by extension boiling point) depend on the strength of intermolecular forces. We say that a compound with stronger intermolecular forces has a lower saturation vapor pressure (i.e., is less volatile).

My Question: If the solute being added to the solution causes there to be stronger intermolecular interactions, wouldn't this cause a lowering in saturation vapor pressure? If so, then the claim that Raoult's Law doesn't depend on the chemical nature of the solute is untrue.

Can someone help me untangle this?

TLDR: If saturation vapor pressure is defined by strength of intermolecular forces, why does dissolving a solute into a solvent lower saturation vapor pressure regardless of its chemical properties when we know for a fact that different solutes have different strengths of intermolecular forces with the solvent?

submitted by /u/NewToUni
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Why does the polynomial x^5 - x + 1 = 0 have no exact solution?

Posted: 24 Nov 2016 10:07 AM PST

I just saw this old Vihart video that mentioned the fact that this polynomial only has an approximate solution, not an exact one. However, when I rearrange the equation into x4 - 1 = -1/x and graph the two individual functions (you can use this online graphing calculator to see), the "approximate" solution of -1.167... is where these two functions cross. Since they are both continuous, differentiable, and cross at this point, why is this only an approximate solution?

submitted by /u/thomprya
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Does receptor downregulation change depending on the frequency of doses?

Posted: 24 Nov 2016 11:20 AM PST

In receptors that get downregulated through agonist application (I understand not all receptors do this). Does giving 6 days 100 mMol (for example) produce the same effect as day 1+ 4 300 mMol. If it doesn't, do we know why? -Dagl

submitted by /u/Dagl1
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Is it possible to make a database where the owner cannot modify information on it?

Posted: 24 Nov 2016 02:55 PM PST

Recent events piqued my curiosity as to if it's possible to encrypt something so as to prevent someone from manipulating the contents in a predictable manner, while still being able to create new content and view it.

Is this possible to do at all? Is it practical to do for your average website, like Reddit?

submitted by /u/Pseudoboss11
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How did Descartes' and Fermat's Analytical Geometry help the development of Newton's and Leibniz's Calculus?

Posted: 24 Nov 2016 06:43 AM PST

How does crossing over "cleanse" chromosomes of mutations?

Posted: 24 Nov 2016 09:46 AM PST

This (really) neat article on white-throated sparrow genetics mentions that mutations accumulate when crossing over does not occur. I'm a little rusty on my molecular bio/genetics and was wondering if someone could enlighten me on how crossing over gets rid of mutations. Thanks.

submitted by /u/mynamenope
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