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Wednesday, May 25, 2016

AskScience AMA Series: I’m Sean Carroll, physicist and author of best-selling book THE BIG PICTURE. Ask Me Anything about the universe and what it means!

AskScience AMA Series: I’m Sean Carroll, physicist and author of best-selling book THE BIG PICTURE. Ask Me Anything about the universe and what it means!


AskScience AMA Series: I’m Sean Carroll, physicist and author of best-selling book THE BIG PICTURE. Ask Me Anything about the universe and what it means!

Posted: 25 May 2016 05:00 AM PDT

I'm a theoretical physicist at the California Institute of Technology, and the author of several books. My research covers fundamental physics and cosmology, including quantum gravity, dark energy, and the arrow of time. I've been a science consultant for a number of movies and TV shows. My new book, THE BIG PICTURE, discusses how different ways we have of talking about the universe all fit together, from particle physics to biology to consciousness and human life. Ask Me Anything!


AskScience AMAs are posted early to give readers a chance to ask questions and vote on the questions of others before the AMA starts. Sean Carroll will begin answering questions around 11 AM PT/2 PM ET.

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If I heat up an iron rod to the point where its glowing, is the iron rod emitting photons or is it just reflecting a higher amount of photons that it normally does at room temperature?

Posted: 24 May 2016 04:27 PM PDT

What makes a stealth plane 'stealth'? What is the technology involved and why can these planes be invisible to radars etc?

Posted: 24 May 2016 05:04 PM PDT

What makes Damascus steel so special?

Posted: 24 May 2016 04:11 PM PDT

I'm not talking about the modern pattern I mean the stuff ancient steel swords were made of that we can't replicate

submitted by /u/AC13verName
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When was it first known and/or confirmed that Mars was another planet and not a star?

Posted: 24 May 2016 06:13 PM PDT

In everything I've read trying to answer this question, Mars is referred to as either a heavenly body or a planet. When did Mars go from being a bright spot in the sky to being recognized as another place like Earth?

If there's a big dumb obvious answer for this that I'm missing, the same question would apply to Venus.

submitted by /u/DoctorBlasphemy
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Why do humans wear clothes and when did we began?

Posted: 24 May 2016 04:58 PM PDT

Do humans wear clothes because we lost our fur or did we lose fur because we began wearing clothes.

submitted by /u/JustStudyItOut
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How can an emotion -such as stress- affect the physical body?

Posted: 24 May 2016 05:49 PM PDT

According to this article here , stress can damage DNA. How is this? Isn't stress just an emotion that is purely in the brain and not quantifiable?

submitted by /u/GassyWizard
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What is the structure of the Australopithecus Afarensis hand?

Posted: 24 May 2016 04:29 PM PDT

Can someone please explain the structure of the hand, and how it worked and its different types of grips.

submitted by /u/Cadd0c
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Does any thing ever appear to exceed the speed of light?

Posted: 24 May 2016 01:14 PM PDT

I'm currently reading Hawking's famous book, A Brief History of Time. Two related questions have popped into my head:

Firstly: From the point of view of a photon, or anything else, does any object, particle or wave - any thing - ever appear to exceed the speed of light?

If not, would the answer be "yes" if, by magic, we could see beyond the "curtain" the limits of the observable universe impose upon us? For example, in an expanding universe, would some distant galaxy appear to be, or actually be, moving away from us faster than light, if we could see to the edge of the universe? Or, perhaps, would we see particles flung outward by the Big Bang in the early nanoseconds of the Universe moving faster than light, if our telescopes could probe such impossible depths of space (and time?)

Secondly: It is my understanding that, due to small fluctuations on the quantum scale, things that would be impossible on the macro scale do happen on the quantum scale. Is it possible, then, that a photon ever actually - not appears to - moves just slightly faster than the speed of light, even for an unimaginably brief period of time?

*For this second question, let's forget about any magic I referred to in the first, such as being able to see straight to the edge of the universe.

submitted by /u/8Milesofshade
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Do objects in space cast shadows on the aurora?

Posted: 24 May 2016 05:50 PM PDT

Would an object like a satellite passing above an aurora interrupt the solar wind?

submitted by /u/OneDayBeRelevant
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What observational evidence is there for calling electron positions "shells"?

Posted: 24 May 2016 04:05 PM PDT

I know the old Bohr model had them as orbits/rings/etc. And now we think of them as shells of statistical probability. But when we say "higher" does that just mean energy, or does the shell actually take up space further away from the nucleus? If so, can we observe that?

submitted by /u/newdefinition
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How do objects leaving Earth overcome their rotational momentum due to the Earth's rotation?

Posted: 24 May 2016 07:47 PM PDT

I couldn't find the answer on google because I can't really phrase my question right. This started with me thinking about what if the Earth stopped rotating? Everything would be thrown in a certain direction due to the momentum from the rotating Earth...

But what about rockets for example? While they are within the atmosphere, they should still be rotating along with the Earth, but once they leave the atmosphere I imagine they shouldn't be affected so much by the Earth- but still retain some momentum?

Maybe they lose their rotational momentum slowly and have negligible rotational momentum by the time they leave the atmosphere, or is it some other reason?

Thanks for reading!

submitted by /u/ROD_OF_AGES
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[Mathematics] How can we know the last digits of Grahams Number, but not the first digits?

Posted: 24 May 2016 07:55 AM PDT

How can we know the last digits at all?

submitted by /u/iKarmaLoL
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Are there any species of octopi that rear their young like mammals and birds do?

Posted: 24 May 2016 03:24 PM PDT

How did civilizations that don't share a common language start to communicate?

Posted: 24 May 2016 04:29 PM PDT

Also how would we communicate with aliens? I assume in a similar way. Assuming they communicate through sound and not some other method.

submitted by /u/XGX787
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What is the best way to reduce the weight of a metal beam while maintaining its structural integrity?

Posted: 24 May 2016 03:48 PM PDT

Me and my friend are trying to reduce the weight of a metal arm in order to decrease the moment of inertia. Our plan is to drill holes in it, and we were wondering what the most efficient way to do that is. A few large holes, lots of small hole, a combination of the two?

submitted by /u/KevinDaellenbach
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If it is recommended to pasteurize fresh squeezed juice, why can I eat the fruit as-is without the same concern for bacteria?

Posted: 24 May 2016 11:04 AM PDT

How is it possible to convert weight into mass?

Posted: 24 May 2016 09:39 PM PDT

From what I understand mass and weight are two completely different measurements, however according to google 1 pound = 453.592 grams.

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Is GP120 found anywhere besides the exterior of an HIV molecule? If yes, where? If no, what traits of the HIV molecule prevent the development of an effective GP120 inhibitor?

Posted: 24 May 2016 03:36 PM PDT

What happens to the growth process of a plant when there are multiple equal light sources?

Posted: 24 May 2016 01:09 PM PDT

Like, plants always grow towards the sun but what direction do they grow in when there are 2 or more light sources on other sides of the plant?

submitted by /u/1auren7
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In reproductive cloning, does Somatic Cell Nuclear Transfer require that the surrogate be different than the somatic cell donor and the oocyte donor to produce a "healthy" clone?

Posted: 24 May 2016 12:02 PM PDT

Edit: I'm wondering what is the minimal number of animals of the same species you need to clone for viable offspring. Could you take an egg and somatic cell from a female and use it as its own surrogate?

submitted by /u/hburggraf
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Why do voltage/current spikes occur when connecting or disconnecting an electrical connection?

Posted: 24 May 2016 01:49 PM PDT

Tuesday, May 24, 2016

American Chemical Society AMA: I am Gerry Wright, Director of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University and Associate Editor of ACS Infectious Diseases. Ask me anything about antibiotic resistance and antibiotic discovery.

American Chemical Society AMA: I am Gerry Wright, Director of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University and Associate Editor of ACS Infectious Diseases. Ask me anything about antibiotic resistance and antibiotic discovery.


American Chemical Society AMA: I am Gerry Wright, Director of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University and Associate Editor of ACS Infectious Diseases. Ask me anything about antibiotic resistance and antibiotic discovery.

Posted: 24 May 2016 04:46 AM PDT

Hi Reddit! I am a Professor of Biochemistry and Biomedical Sciences at McMaster Univeristy and Director of the Michael G. DeGroote Institute for Infectious Disease Research (http://mcmasteriidr.ca/). I have been working on antibiotic resistance and discovery for over 25 years. My lab uses a combination of chemistry, microbiology, biochemistry and genomics to understand how antibiotics work, along with exploring mechanisms and evolution of resistance. We use this information to learn how to find new antibiotics and alternatives to antibiotics.

I am also an Associate Editor of the journal ACS Infectious Diseases (http://pubs.acs.org/page/aidcbc/editors.html), a publication that highlights how chemistry sheds light on and helps in the fight against pathogens.

I am happy to answer any questions you may have on antibiotic resistance and discovery.

I will be back at 1 pm ET, ask anything.

submitted by /u/AmerChemSocietyAMA
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Why did heavy-lift launch vehicles use spherical fuel tanks instead of cylindrical ones?

Posted: 23 May 2016 09:32 AM PDT

If you look at the cutaways of the Saturn V and N-1 in this webpage you can see that the fuel tanks taper away from the inner sides of the spaceship due to their spherical nature. Why didn't they use the full space available to them?

submitted by /u/8BandComp
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Can space-time warp in such a way as to allow me to start a journey and then return as my mirror image?

Posted: 24 May 2016 02:29 AM PDT

How do we find out if electrons are not elementary?

Posted: 23 May 2016 10:35 AM PDT

What experiments can or have been done to confirm this being true or false?

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Is there a continuous version of product, like integrals for sums?

Posted: 23 May 2016 11:36 AM PDT

Are there weird Karman Lines on other planets?

Posted: 23 May 2016 10:27 AM PDT

The Karman Line is about 100km on Earth, and that's where in order for an aircraft to generate lift against the atmosphere you need to be travelling faster than what it takes to maintain stable orbit.

I'm having a hard time turning this over in my head for places like Jupiter, Venus and Titan.

submitted by /u/accidentallybrill
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Are the three spatial dimensions actually one dimension, represented by three vectors? Are the three dimensions actually "separate"?

Posted: 23 May 2016 10:07 AM PDT

While we represent position in three dimensional space using three coordinates, it occurred to me that the universe may not have a discrete x, y, and z axis. If these dimensions can be mixed in to each other depending on your reference frame, are they really a separate phenomenon?

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How does citric acid stop oxidation?

Posted: 24 May 2016 03:12 AM PDT

Why are images of the same width and height so different in file size?

Posted: 24 May 2016 04:08 AM PDT

Whenever I create some image in Photoshop and save it (lets say 1920x1080px) it's like 1MB file size. When I blur the entire image it's suddenly only 100KB.

Why is there a difference in file size, doesn't the image have to 'remember' which color what pixel is, regardless of how sharp/blurred or clean/messy an image is? It still has the same amount of pixels.

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What are nano-photovoltaic cells?

Posted: 24 May 2016 03:12 AM PDT

I am studying a little about research ongoing in Solar energy. It seems that research in nano-PV has increased over the time.

Please shed some lights on efficiency too, how are they doing against our current PV technology? better or worse? As I am no expert in this domain please throw away any information you have. I would really appreciate it.

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Is there a complete topographic dataset of Earth?

Posted: 24 May 2016 02:53 AM PDT

As the title says, I am searching for complete topographic data of the entire planet. SRTM is the closest I could find so far, but it covers only about 80% of the area of the planet. Is there a way to get more of the data?

submitted by /u/notsofunnynowehh
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How does a planet's orbit change as one of the suns in a binary-sun solar system starts do 'die'?

Posted: 24 May 2016 02:51 AM PDT

Given a solar system with a binary sun, where one of the suns is noticeably smaller than the other; given that such a system has only one planet with its companion moon.

The smaller sun starts to die. Will the orbit of the lone planet expand or contract? Will that planet's year get longer or shorter as the sun dies off?

Thanks!

submitted by /u/DrVialgo
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So when two black holes collide they form a bigger one, but what if a black hole were to collide with a white hole?

Posted: 24 May 2016 03:24 AM PDT

also what if this black hole is connected to that specific 'white hole'

submitted by /u/AgilityBobblehead
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Are the number of electrons equal to the number of protons in the universe?

Posted: 23 May 2016 09:22 PM PDT

Why are 5 independent slip systems needed for arbitrary deformation?

Posted: 23 May 2016 09:52 AM PDT

So the Von Mises Criterion says we need 5 active slip systems, but why are 3 not enough for a 3 dimensional object??

submitted by /u/MmmmmmmmDonuts
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What really causes Hematite stones to crack or break?

Posted: 23 May 2016 06:30 PM PDT

When Googling the question, all that comes up is the new age answer, "that it absorbs negativity."

What really causes hematite to break after sitting around for a few years?

submitted by /u/geotagger
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Are there any math problems that even a computer could not solve?

Posted: 23 May 2016 03:10 PM PDT

Edit: To those wondering what I mean by "math problem," I simply mean any problem that involves math, or basic logic. Does that makes sense?

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Can sound frequencies break anything?

Posted: 23 May 2016 08:46 AM PDT

So when someone sings loud enough to break glass they're matching the frequency of the glass. And if everything in life has a frequency does that mean that if the specific frequency of any substance is matched it will break?

submitted by /u/relljr
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Why is such a large portion of our star systems mass concentrated at the Sun?

Posted: 23 May 2016 09:15 AM PDT

The Sun contains about 99.9% of all the mass in our star system, but in some other star systems the mass is spread enough to form orbiting brown dwarfs, binary stars and what not. What is it in a star systems formation that causes them to have such huge differences between each other on mass distribution?

submitted by /u/empire314
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Are there any pathogenic (to humans) archaea?

Posted: 23 May 2016 07:44 AM PDT

Monday, May 23, 2016

Are things like peanut butter, cream cheese, jellies etc. considered a liquid or a solid?

Are things like peanut butter, cream cheese, jellies etc. considered a liquid or a solid?


Are things like peanut butter, cream cheese, jellies etc. considered a liquid or a solid?

Posted: 22 May 2016 04:35 PM PDT

Do planetary orbits cause measurable "tides" on the surface of the sun?

Posted: 22 May 2016 02:39 PM PDT

Does this affect sunspots and solar storms when the planets line up?

submitted by /u/TheBlueCoyote
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When one stands on the moon, would the horizon appear to be closer, since the moon is so much smaller than earth?

Posted: 22 May 2016 11:40 PM PDT

Have we ever converted energy to mass?

Posted: 22 May 2016 11:17 PM PDT

If a disc was spun at 1 RPM, how large would this disc need to be in order for the edge of it to reach the speed of light?

Posted: 22 May 2016 09:53 PM PDT

Such a weird question, but I've been thinking about this for much longer than I'd like to admit.

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How can you have ohmic resistors if resistance causes heat increase and heat increase causes higher resistance?

Posted: 22 May 2016 12:44 PM PDT

So filament lamps are non-ohmic because if you increase the voltage across them then the charge carriers disipate more energy in the resistance of the lamp, causing it to heat up, increasing the resistance, and therefore reducing the increase in current with each increase in voltage. Therefore they are not proportional and therefore it is non-ohmic.

With an ohmic resistor, surely as current passes through the resistor, the resistor heats up and increases in resistance just like with the filament lamp and therefore not ohmic because the resistance is changing?

Or am I missing something?

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Could a fiber-optic cable be modified to work as a periscope?

Posted: 22 May 2016 10:52 PM PDT

We were learning about fiber optics in school and my mind started wandering and it got me wondering…normally in a fiber optic cable the light from the incoming image ends up horribly distorted before it comes out the other end because of the amount of times it reflects of the inside "walls" of the cable, but if you could have a cable made of say a million or so cables within a cable, each cable could carry a unique signal or point of light like a pixel on a tv screen. So, if you could take an image and focus it into a small area using a lens (or series of lenses), an area probably close to the point where all the rays of light converge, you could then transfer the image through the cable and then do the reverse process on the other side where the image could be projected on to a screen.

I don't see why this wouldn't work, besides the construction challenges. To create a 1MP image would require a million individual (optically insulated) cables which would have to be very small. If they were, say 9μm in diameter, you could fit 1,000,000 of them in a 3mm2 area

Maybe it has already been done, and i think there could be many applications for this if it was economical to produce, not to mention the novelty factor, but i get the feeling that the cost to produce something like this would not be worthwhile in a world where everything is digital.

submitted by /u/TheRealFalconFlurry
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The Earth is an oblate spheroid, but what about the atmosphere? Does it fit the shape of the Earth or is it more perfectly spherical?

Posted: 22 May 2016 08:23 AM PDT

I was reading about how Everest is the highest point above sea level, but Mount Chimborazo is the farthest point on Earth from the center. Does the atmosphere fit these bulges in the Earth's shape? Or does it fit as a sphere around Earth? If the atmosphere is perfectly spherical, the air at the top of Chimborazo would be thinner than at the top of Everest, right?

submitted by /u/agoyalwm
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Do gravitational waves/gravitons have angular momentum?

Posted: 22 May 2016 08:46 PM PDT

Why can there not be an n=0 mode on a waveguide?

Posted: 22 May 2016 01:04 PM PDT

Take an elastic membrane for example.

http://people.seas.harvard.edu/~jones/ap216/lectures/ls_1/ls1_u8/ls1_unit_8104.gif

My physics notes say there has to be at least one oscillation in the x direction: why can it not be flat in the x direction, and a wave travelling down the z direction like normal?

submitted by /u/eebootwo
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What is the origin of the stellar types classification letters?

Posted: 23 May 2016 12:44 AM PDT

Hi everybody!

Does anybody know why the spectral types are called like that, i.e. O, B, A, F etc?

submitted by /u/ivanmarvin
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How did scientist succeed to create an acoustic black hole ?

Posted: 22 May 2016 08:34 PM PDT

Is it possible to know what color a material will be without actually seeing it?

Posted: 22 May 2016 11:58 AM PDT

If so, what details would you need to know?

submitted by /u/BLACKAP3RTURE
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How does the body cope with the presence of heavy metals in the circulation?

Posted: 22 May 2016 07:42 AM PDT

When I did my Osteopathy undergraduate degree many years ago, I recall learning that molecules with a molecular mass greater than six kilo-Daltons could not pass through the basement membrane of the kidney, which meant that heavy metals such as mercury and lead (and other nasties such as DDT) could not be excreted, and were consequently stored in the liver until death. Yet, in the 19th century, hatters were driven mad by mercury. (Hence, the behaviour of the Mad Hatter in 'Alice in Wonderland.'). For this to happen, I assume at least some of the mercury must have not been stored but have been free-floating in the circulation and made its way to the brain. Can anyone throw some light on this?

submitted by /u/Vincent_Black_Shadow
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Why are frozen-then-thawed bananas so sweet?

Posted: 22 May 2016 07:41 AM PDT

We peel and freeze bananas for smoothies. I accidentally let one thaw. It's predictably mushy, but also unbelievably sweet. Where does all that sugar come from?

submitted by /u/daveberzack
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