astrophysics-unleashed

[astrophysics-unleashed]

Hi followers!

dahlek here. Obviously there hasn’t been a lot of activity on this blog recently, mostly due to the three of us being busy with school and other pursuits. I’ve decided to make my own way in the world and create my own blog that I hope to post to relatively frequently (I think I waste a lot more time on tumblr than my two colleagues). It’ll follow the same format as Astrophysics Unleashed but it’ll be just me running it and posting stuff more often.

So if you’d like to give me a follow, click here!

Feel free to send me questions on topics you’re curious about, current events, life as a grad student, whatever. I love answering questions so definitely don’t be shy.

Thanks everyone,

Emma

[astrophysics-unleashed]

Anyone have any questions?

Greetings tumblr!! First off, thank you all for following us and showing interest in the Universe. We here at AU appreciate your curiosity and are honored to answer your questions.

At the request of our followers, we’d like to be more active with our blog. I am currently working on a “review”-- more appropriately an analysis--of Christopher Nolan’s Interstellar (2014) which I think will be interesting and which I think y’all will enjoy. However, the quickest, sure-fire way to get this party started is to take in as many questions as possible! 

So, with that in mind I would like to ask you all to do this one task: ask us questions! Whether it’s one that’s been bugging you for a long time, or it has something to do with a movie, ask us! Don’t really have a question? No problem! If you come across any (science-y) thing on Tumblr or whatever that you want to explore, attach a link to a message and ask us about it!! Maybe we’ll have an answer, maybe we won’t, but at least we’ll think about it together!

-Orion

astrophysics-unleashed

[astrophysics-unleashed]

love the blog! would like to see more activity if possible!

Yes, agreed! We’ve all recently earned our Bachelor’s degrees and are all busy with life, so our activity has dwindled. Thank you all for your continued interest in our blog and in science! Also, remember to ask us any questions about the great void. We’ll do our best our best to answer them.

Much love,

The Astrophysics-Unleashed Team

[astrophysics-unleashed]

Hi! . . Why does light sometimes behave as a wave, and sometimes as a particle? And what is a "light wave" anyways? I guess photons are the "particle" aspect of light? So many questions! Thanks! :)

Hello there! Excellent question!! Light is a very strange thing, when you really stop and think about it. The wave-particle duality of light (of all matter, really) is really interesting and rather difficult to explain, but here goes. The really short answer is probably, “Quantum Mechanics” or something, but that would be a rather boring and unsatisfying answer. DKS wrote a bit about explaining what light is in an earlier post and I wrote another bit explaining what it is that waves when we talk about light waves.

Let’s first look at your first question, “Why does light sometimes behave as a wave, and sometimes as a particle?” I first have to correct the question–light doesn’t “sometimes behave as a wave” nor does it “sometimes [behave] as a particle.” Light always behaves as a wave and as a particle, both at the same time; it’s not as if sometimes we’re running an experiment and light suddenly acts like a particle instead of a wave. Instead what happens is that when we treat light as a wave and run experiments as such, the results of such experiments can best be explained if light were a wave. The same is true if we treat light as a particle. Sounds a little like tautological/circular logic, but let me explain it a bit more.

Light As a Wave:

There are a whole bunch of awesome experiments that show that light is a wave; these experiments are called the Multi-Slit Experiments. They are set up with a light source (nowadays, the light source is usually a L.A.S.E.R.), an obstacle (usually a screen, like a wall, with one or more small openings in a line to allow light to pass through), and then a plain and boring wall where we can see the light of the LASER (you can replace the wall with an array of photodetectors to measure the strength of incident light). Something like this: 

or like this: 

What happens is that when you shine light at the hole in the obstacle (the thing labeled “slit partition” in the top image, and the unlabeled wall in the second image), you get a series of bright and dim spots on your wall (labeled “Interference Light and Dark Fringes” in the top image) that look like this. These are called interference patterns, and they occur because light behaves like a wave (really, light interferes with itself just like water waves do. Here’s a cool video). This interference occurs when the slit(s) is/are tiny: usually they are about the size of the wavelength of light you’re using. For red light (λ ≈ 600nm = 0.6μm) you want the slit to be at around that width for best diffraction. If light only behaved as a particle (photons), then you would expect the photons to simply pass through the opening, hit the wall at that one spot, and create a single point of light. However, this is demonstrably no the case! It doesn’t make sense to treat light as a particle when doing the multi-slit experiments because that model is unable to predict interference patterns.

Light As a Particle:

Treating light as a wave means that there are an infinite number of energies that light can carry: it would be a smooth spectrum. There is nothing in those experiments that contradict that possibility. However, Albert Einstein’s Nobel-prize winning 1905 explanation for the photoelectric effect proved that the energies of light are not infinitely smooth, but are actually quantized energy levels. These “quantized energy levels” are called photons.

Light As Both a Wave and Particle, A Quantum Mechanical Approach:

Basically, whatever light is (we’re not really sure exactly WHAT light is, but we have some pretty cool ideas) sometimes it’s best to think of it as a particle, other times it’s more helpful to think about it as a wave. We know that light follows the Electromagnetic wave equation, and the Planck relation, E=h*ƒ. The wave equation explains light’s wave-like properties, the Planck relation explains light’s particle-like properties. Interestingly enough, applying Einstein’s famous energy equation, E=m*c^2, for objects with mass we can see that 

E = m*c^2      and       E = h*ƒ.

Energy is energy, doesn’t matter what form it’s in, so by combining the two, we get,

mc^2 = hƒ.

Now, a thing to note is that the speed of light, c, the wavelength of light, λ, and the frequency of light, ƒ, are related by the following equation,

c = λƒ.

Thus,       ƒ = c/λ.

Plugging that into mc^2 = hƒ we get,

mc^2 = h (c/λ) = hc/λ.

Dividing everything by the speed of light, c, we get,

m*c = h/λ.

Interestingly enough, the momentum p of a particle of mass m and speed v is simply the product of the two, p = mv. What this means is that the product m*c is the momentum of a photon, which has a value of h/λ; massless object carries momentum!! Likewise, this equation means that the (de Broglie) wavelength of a particle (e.g., an electron, proton, neutron, baseball, etc.) is h/(m*c); a seemingly solid object is also a wave!! This gets us into the realm of quantum mechanics, wave functions, Schrodinger’s equation, and the thought experiment known as Schrodinger’s Cat.

Yea, OK, Nice Story But is Any of That Real?!

Whether a thing is real or not is not really what’s at debate here. The real question is whether this stuff helps us understand strange phenomena. The math predicts that solid objects will behave like waves under specific conditions; it predicts that a massive object (relatively speaking with respect to massless photons) can experience the same interference patterns from the multi-slit experiment that photons experience. So scientists tested this hypothesis and guess what happened: 

molecules exhibited the exact same interference patterns!! Crazy!!

If you’re still reading after that wall of text, thank you for time!! I’m sure you have many more questions so please, please, please feel free to ask them all!! We’ll do our best to answer them!

-Orion

astrophysics-unleashed

[astrophysics-unleashed]

What is the weight of the particle 2 4 He in kg?

Assuming you’re talking about the mass of a single helium-4 atom:

Then it’s mass is tiny: wolframalpha.com says that the mass of a helium atom is ≈ 6.64648e-27 kg (http://www.wolframalpha.com/input/?i=mass+of+helium+atom).

Helium-4 has 2 protons and 2 neutrons. The mass of a proton ≈ 1.67e-27 kg, the mass of a neutron ≈ 1.67e-27 kg. At only 3 significant figures (just going to the hundredths place and no further) the proton and neutron have the same mass (in reality, the values differ by the mass of an electron and neutrino) so all you do multiply 1.67e-27 * 4 = 6.68e-27 kg, which is approximately the value wolframalpha gave us. If we cared to be more accurate about the mass of the proton and the neutron then we’d get a value close to wolframalpha. 

Thanks for asking!

-Orion

astrophysics-unleashed

[astrophysics-unleashed]

Hey! Hear your plug on stuff you should know. You dudes have some cool stuff here

this is a super late reply but hey, thanks!

-dahlek

astrophysics-unleashed

[astrophysics-unleashed]

Informative video from NASA on what to look for in the night sky this month.

-dahlek

astrophysics-unleashed

[astrophysics-unleashed]

An incredible photo taken by Italian astronaut Sam Cristoforetti aboard the ISS. Posted with the subtitle "Good night from space! Buona notte dallo spazio!"

-dahlek

astrophysics-unleashed

[astrophysics-unleashed]

There's nothing like a little perspective.

-DKS

astrophysics-unleashed

[astrophysics-unleashed]

-DKS

astrophysics-unleashed

[astrophysics-unleashed]

A quick addition: Orion talked about gravitational waves as waves that vibrate through space-time itself. Here’s a cool link to a TED talk that describes this predicted phenomenon and presents some of the computer models that have simulated what these waves would ‘sound’ like.

https://www.ted.com/talks/janna_levin_the_sound_the_universe_makes

-DKS

astrophysics-unleashed

Me again :) thank you for answering my question before. It was really helpful. I have another question, if it's okay. Okay, so light and radio waves are waves, but what /is/ waves? Is it waves in the fabric of spacetime? And how does radioes work? :) again, thank you so much for explaining this :)

Hi again myfantasticdoctor,

For a quick reference, I would like to point you to DKS’s earlier post on what light is, “What is Light?” I think he answers this question rather elegantly, but I’ll take a stab at it, too, just in case I make a good point. The short answer to your questions are in «this kind of format» and the long answer is everything else.

For Radios:

«Radios work like this: radio receivers (like a boombox, or car radio) usually have some kind of antenna that’s made out of metal and these antennae detect the radio signals coming from a radio broadcasting station (basically a bigger and stronger “reverse antenna”). The radio signals from the station make the electrons in the receiver’s antenna move up and down along the length of the antenna; moving electrons = current so those radio waves induce a current along the length of the antenna. This signal passes through circuits that clean up (remove noise) and boost the signal. The processed signal is then fed into a speaker and it causes the drum of the speaker to vibrate. That is what we hear on the other end of the radio!»

For light:

I’m gonna start kinda at the beginning and define a few things so that we don’t have any confusion or miscommunication, so bear with me.

Let’s define “light” to mean anything that is part of the Electromagnetic Spectrum; by this definition Gamma Rays, X-Rays (like the ones dentists use), Ultraviolet (the stuff for which you use sunblock), all colors in the rainbow (remember ROY G BIV?), Infrared (the heat we feel coming from a fire), Microwaves, and Radio waves are all light, since they are part of the Electromagnetic Spectrum.

Each different name (e.g., Gamma Ray, Infrared, or Radio) corresponds to a different section of the Electromagnetic Spectrum and is defined by a range of “wavelengths” or by a range of “frequencies.” These terms, “wavelength” and “frequency,” are also used to describe things that travel in waves (e.g., water waves, sound waves) and they make a sort of sense when we actually see the waves.

Now here is where we get to your question: if sound waves are carried through the air (sound waves can also travel through rock, and even the whole Earth!) and water waves are carried through water, what carries light waves? «The answer is that /nothing/ carries light waves. Light is a self-propagating wave!

Light is an oscillating electromagnetic field; an electric field changes with time, which changes a magnetic field with time, which changes the electric field, and so on and so forth. Naturally, you want to ask  about what caused the electric field to change in the first place? The answer is that electric charges (e.g., electrons or protons) create electric fields and when the charges move, their electric fields change and thus they produce oscillating electromagnetic fields as described above. /That/ is what light is and /that/ is what is waving. Here’s a neat visualization: (http://www.srh.noaa.gov/jetstream/remote/images/emwave.gif)» The “wavelengths” are still measurements of peak-to-peak distances, and the “frequencies” are still measurements of how many peaks pass over time. That’s why we think of them as waves.

Extra credit:

You brought up a really interesting phenomenon: waves of spacetime fabric. That is an actual thing; spacetime is actually really squishy when you have mass, and the more mass you have the more squishy spacetime becomes. When you have something really dense, such as a neutron star or a black hole, in orbit around some other thing that is also really dense (so a neutron binary system, or black hole binary, or neutron-black hole binary) you stretch the fabric of spacetime in a very periodic way and that distortion of spacetime actually propagates outwards and travels away from the system. These kind of spacetime waves are called Gravitational Waves and, although we have yet to directly detect them, we have really excellent mathematical and physical models that predict their existence. So maybe I should’t say that they are actual things yet, but I would be surprised i they don’t actually exist.

-Orion

As always, thank you for your questions! I want to make sure you and all our followers continue asking us cool questions like this! Even if you don’t think it’s a “cool” question (please don’t ever think anything is a “stupid” question) ask it! The reality of our universe is pretty bizarre sometimes and you never know which question might lead to bizarro world!

[astrophysics-unleashed]

Me again :) thank you for answering my question before. It was really helpful. I have another question, if it's okay. Okay, so light and radio waves are waves, but what /is/ waves? Is it waves in the fabric of spacetime? And how does radioes work? :) again, thank you so much for explaining this :)

Hi again myfantasticdoctor,

For a quick reference, I would like to point you to DKS’s earlier post on what light is, “What is Light?” I think he answers this question rather elegantly, but I’ll take a stab at it, too, just in case I make a good point. The short answer to your questions are in «this kind of format» and the long answer is everything else.

For Radios:

«Radios work like this: radio receivers (like a boombox, or car radio) usually have some kind of antenna that’s made out of metal and these antennae detect the radio signals coming from a radio broadcasting station (basically a bigger and stronger “reverse antenna”). The radio signals from the station make the electrons in the receiver’s antenna move up and down along the length of the antenna; moving electrons = current so those radio waves induce a current along the length of the antenna. This signal passes through circuits that clean up (remove noise) and boost the signal. The processed signal is then fed into a speaker and it causes the drum of the speaker to vibrate. That is what we hear on the other end of the radio!»

For light:

I’m gonna start kinda at the beginning and define a few things so that we don’t have any confusion or miscommunication, so bear with me.

Let’s define “light” to mean anything that is part of the Electromagnetic Spectrum; by this definition Gamma Rays, X-Rays (like the ones dentists use), Ultraviolet (the stuff for which you use sunblock), all colors in the rainbow (remember ROY G BIV?), Infrared (the heat we feel coming from a fire), Microwaves, and Radio waves are all light, since they are part of the Electromagnetic Spectrum.

Each different name (e.g., Gamma Ray, Infrared, or Radio) corresponds to a different section of the Electromagnetic Spectrum and is defined by a range of “wavelengths” or by a range of “frequencies.” These terms, “wavelength” and “frequency,” are also used to describe things that travel in waves (e.g., water waves, sound waves) and they make a sort of sense when we actually see the waves.

Now here is where we get to your question: if sound waves are carried through the air (sound waves can also travel through rock, and even the whole Earth!) and water waves are carried through water, what carries light waves? «The answer is that /nothing/ carries light waves. Light is a self-propagating wave!

Light is an oscillating electromagnetic field; an electric field changes with time, which changes a magnetic field with time, which changes the electric field, and so on and so forth. Naturally, you want to ask  about what caused the electric field to change in the first place? The answer is that electric charges (e.g., electrons or protons) create electric fields and when the charges move, their electric fields change and thus they produce oscillating electromagnetic fields as described above. /That/ is what light is and /that/ is what is waving. Here’s a neat visualization: (http://www.srh.noaa.gov/jetstream/remote/images/emwave.gif)» The “wavelengths” are still measurements of peak-to-peak distances, and the “frequencies” are still measurements of how many peaks pass over time. That’s why we think of them as waves.

Extra credit:

You brought up a really interesting phenomenon: waves of spacetime fabric. That is an actual thing; spacetime is actually really squishy when you have mass, and the more mass you have the more squishy spacetime becomes. When you have something really dense, such as a neutron star or a black hole, in orbit around some other thing that is also really dense (so a neutron binary system, or black hole binary, or neutron-black hole binary) you stretch the fabric of spacetime in a very periodic way and that distortion of spacetime actually propagates outwards and travels away from the system. These kind of spacetime waves are called Gravitational Waves and, although we have yet to directly detect them, we have really excellent mathematical and physical models that predict their existence. So maybe I should’t say that they are actual things yet, but I would be surprised i they don’t actually exist.

-Orion

As always, thank you for your questions! I want to make sure you and all our followers continue asking us cool questions like this! Even if you don’t think it’s a “cool” question (please don’t ever think anything is a “stupid” question) ask it! The reality of our universe is pretty bizarre sometimes and you never know which question might lead to bizarro world!

astrophysics-unleashed

[astrophysics-unleashed]

Well, ilovedrinkingbathwater, keep asking us questions! We’ll do our best to answer them! The three of us really enjoy talking about all the crazy aspects of the universe. We don’t have all the answers, but we can all work towards a greater understanding if we discuss the problems! :D

-Orion

astrophysics-unleashed

Can you help me understand time? Is it a what or a where or when or a combination thereof? I sometimes think I have it and then my brain is like nope and then I don't have it. Could you help me please?

I think the best way to think of time is as a dimension, an addition to the three spatial dimensions we’re so familiar with. Think of it as a sort of sequence of x-y-z coordinate systems, as a continuous march of 3D sequences. So in that sense, it’s a what. You’ve probably heard of the word spacetime; it’s a combination of the three spatial dimensions and the fourth dimension of time into a single continuum. This 4D coordinate system makes it easy to describe where an event takes place: all you need are it’s x, y, and z coordinates, and also the time t at which the event takes place in the continuum. So in the case of spacetime, time is a where. And I guess it’s a when if you consider the way humans perceive it; we can see all three spatial dimensions simultaneously, but only the instantaneous moment of time is available for us to access. But yeah, time is a weird thing.

Another cool thing about time is that it’s relative. That is, people moving at different speeds experience time differently. Before Einstein’s revolutionary theory of special relativity, it was generally accepted that an event recorded by someone sitting on Earth and someone flying by at the speed of light would produce the same results. But it doesn’t; this is called time dilation. Say you’re sitting on the Earth, holding a clock, so it’s not moving in your reference frame. Someone zips by at half the speed of light with their own clock on board. You read the clocks and compare the two, and after your clock has ticked once, the spaceship’s hasn’t yet. To you, the observer, time appears to slow down on the spaceship. But to the people on the spaceship, time is moving by normally. Time dilation happens all the time, but since we as humans are moving so slowly relative to each other, we can’t notice it. But once you start moving closer to the speed of light, its effects become more prominent. For example, GPS devices that use satellites that are orbiting the Earth so quickly need to account for relativistic effects so you can get accurate maps on your phone.

But yeah, time is weird. Thanks so much for your question! Hope this helps.dahlek

[astrophysics-unleashed]

How difficult is photometry? Do you just point a telescope at a star, hook it up to your laptop, and get data points? What are some of the labs you do in your classes? What are the professors like? - Zafar

Photometry is actually fairly complex when you get into the nitty gritty of it. I’ll try to sum it up in a concise and oversimplified way here. If you want more depth just ask about a specific part of this answer.

The idea is to turn a picture into something that’s scientifically significant. We don’t want to just take pretty pictures, we want to know how much energy hit our detector in each image so we can do real science. That’s where photometry comes in. Let’s start at the beginning.

When you take an image of a star, the nature of the detector that you’re using ensures that your data will be polluted. The heat within your detector will add to your signal (thermal noise),  and your detector will not be completely uniform (maybe there’s some dust on a few pixels that makes them absorb light more slowly). There are also other forms of noise that apply here but I’ve decided not to include them. The first step into extracting data from your image is to negate this noise.

Concerning the thermal noise, standard practice is to take an image of the same exposure time as the image of your star, but with the camera shutter closed. Theoretically all the light in this ‘calibration image’ will be from thermal noise. Once you have this image, simply subtract it from your star image.

To fix the nonuniform detector we generally take exposures of a uniform light source. In theory, every pixel in this image should have the same number of counts. The differences detected between the counts, then, exactly map the non-uniformity of the detector. Normalize this image to the mean and then divide your star image by it, and you’ve corrected the non-uniformity problem.

As I write this I’m realizing that it’s not very concise… there’s just too much to cover… oops. Sorry for the length.

Next problem: the atmosphere. In theory, the light received from a point source should have a Gaussian distribution. Turbulent atmospheres like the Earths cause the light to bend constantly in unpredictable ways, and the light will spread out across your detector. This isn’t always a problem, but often some sort of Gaussian fitting routine is required. This is a process by which you take all the counts on your detector that are spread out by the atmosphere and shove them back into a Gaussian shape, essentially recreating what the star would have looked like if the atmosphere didn’t mess with it. 

If you’re still reading this that means that this way-too-long explanation is somehow interesting to you (which means that you’re awesome). Unfortunately we’re not at the end. We want the energy from the star and there will always be some form of background noise in your image (often called the sky level) contributing to your signal. In its simplest form, this can be corrected by simply taking an average of the background of the image and subtracting it. 

Ok, we can finally count up the energy given to us by the star! But… the units are meaningless. While the units you’re counting are pure energy units, they’re just pixel counts… they’re not Joules or electron volts or magnitudes or anything. If your application requires you to have the energy of the star in standard scientific units you have one more step: standard fields. Take an image of a star that has a known energy (called a standard star). Do the same above steps for this star. Since you know this stars energy and you know the amount of pixel counts that this star gave you, you now have a conversion factor.

Aaaaand breath.

Moving on to the other parts of your question. We do all sorts of intro labs at Whitman involving observations, computer simulations, and using ancient methods to re-create major astronomical discoveries in an authentic way. The upper-level labs are much more open-ended. Orion and I collaborated our Junior year to do photometry on all of the stars in the Big Dipper. We then used our results and the distance modulus to plot the stars of the Big Dipper in 3 dimensions. Then we could move our point of view and see what the constellation (Asterism technically I guess) looks like from other parts of the galaxy. A couple of my friends’ upper-level labs were to observationally determine the radii of the Jovian moons and to determine the rotation period of the Sun by tracking sunspots (I think). 

Since this post is already way too long I’ll just say that we have 2 professors and they are both incredible.

-DKS

astrophysics-unleashed

[astrophysics-unleashed]

The Planetary Science books we used was Fundamental Planetary Science by Lissauer and de Pater

I agree with DKS’s choices, but would like to add Introductory Astronomy and Astrophysics, 4e by Zeilik and Gregory. This was THE reference book for me throughout my studies. I always went back to it when I forgot some detail. It’s pretty math intensive and pretty comprehensive. The only downside to it is that the 4e is from 1998, so some information is out of date.

If you’re into bind-bending books (or as dahlek and I like say, cerebral), pick up a copy of Black Holes and Other Cosmic Quandaries by Neil deGrasse Tyson. Pretty cool stuff.

-Orion

Never apologize for asking us these kinds of questions, consciousness-arose! Just don’t ask inappropriate questions, and we’re all happy.

astrophysics-unleashed

Hi another question! (sorry). What textbooks did you use for your planetary science classes? Are there any astrophysics textbooks that you particularly liked? - Zafar

I wasn’t in Planetary so I can’t give you the book we used there (Orion or Dahlek…) 

For me, there’s no one textbook that encompasses the entire subject of astronomy. Instead, there are a bunch of great textbooks that focus on specific branches of the subject. Here are some that stood out for me through college.

Astronomy:

Introduction to Cosmology by Ryden was great. All the other texts I used for astro specifically were alright, but I don’t feel like they were good enough to mention here.

Physics:

Quantum Physics by Townsend.

Anything by Griffiths (he has an E&M book, a particle physics book, and a quantum book).

Thermal Physics by Schroeder (I loved this, I expect my fellow bloggers may disagree).

If you’re looking for some interesting reading that takes you on a journey through the universe I’d also recommend a Brief History of Time by Stephen Hawking.

-DKS

[astrophysics-unleashed]

Can I ask something about physics? Since light is waves and sound also is waves, would it be possible (not for humans, just generally) to hear light and see radio waves. If so, how would it sound, and how would it look? Thanks :)

Hello myfantasticdoctor, thank you for asking this. This is an interesting question and the answer isn’t too bizarre. The short answer is in «italicized bold face», the long answer is everything else.

Let’s first address seeing radio waves:

This one is fairly easy: «if you could see radio waves, it would look like any other form of light»; a radio broadcasting station would appear to be a bright light that pulses (the pulsing comes from amplitude modulated, or AM, waves) and shifts colors (frequency modulated, or FM, waves). This is because Radio Waves are part of the electromagnetic spectrum, which means that it IS light. See DKS’s earlier post on what light is, What Is Light? If you want to know how radios work, we can answer that question, too! :)

«Buildings would appear transparent, but not totally invisible, and would look ever-so-slightly hazy». That’s because radio waves can penetrate through a lot of materials, but not without losing some of it’s power. Transparency and opacity are both measure of how much light passes through a material, and it changes depending the wavelength of light. «So if we could see radio waves, it would look like any other form of light, just with a color we can’t even conceive. Here’s a cool visualization of what we’re talking about, except that the source of radio waves is a celestial body» 

(Source: http://apod.nasa.gov/apod/ap110413.html)

The link provides a great explanation, but the gist is that the purple stuff is all emitting radio waves only we’ve just given it the color purple. In reality, that cloud would /not/ look purple, because purple light is a well defined color (meaning that it has a very specific range of wavelengths that are not in the radio). Each dot that appears in the sky in this image is not actually a star, but a galaxy that is enormously bright in the radio. Pretty cool!

Now let’s talk about hearing light:

That one is a little bit complicated. Hearing as we know it requires pressure waves, aka, sound waves. The pressure waves in the air collide with the tympanic membrane (http://img.medscape.com/pi/emed/ckb/otolaryngology/834279-858557-858684-1755980.jpg) in our ears and that vibrates some bones, which then stimulates something or other (some physiological process occurs) and that gets converted into electrical signals that are sent into our brain and we interpret it as sound. Light, however, doesn’t travel via pressure waves. Sound needs to travel through some material; light doesn’t have that restriction.

So light cannot create a pressure wave, so we have to think of a mechanism that converts light into “sound”. I can think of two ways to do this: either we convert light into pressure waves, or we convert light into electrical signals. Converting into pressure waves would create what we humans would call sound and that’s easy: car radios, TVs, cellphones, tablets all receive information as light (usually microwave, sometimes radio wave) via an antenna, convert the light into electrical signals, which then drive speakers, which create pressure waves, which we interpret as sound. That’s how radio astronomy /used/ to be done: radio astronomers would point their radios at the sky and listen to the radio waves coming from the sky. You get to hear really cool things like pulsars (http://www.jb.man.ac.uk/pulsar/Education/Sounds/), or if you convert wifi signals (usually operate in the microwave-radio wave range) into sound, you get this (http://www.wired.com/2014/12/guys-hacked-hearing-aids-let-listen-wi-fi-networks/)

But that’s kind of boring and only works for humans because we can only hear via pressure waves (Joking. That is not at all boring, but effing awesome!); let’s try to imagine what light could sound like to an organism that /evolved/ to hear light. In order to do that, it (evolution) would probably have taken advantage of the fact that light can behave as a particle and carry momentum like a particle. We’ve all heard about Einstein’s E=mc^2, but have you ever thought about the fact that this means that ‘mass’ and ‘energy’ are equivalent quantities? They’re the same thing, just viewed from a different angle? Since light carries energy, it carries momentum. This momentum can be used to kick electrons out of a metal plate, a process known as the Photoelectric Effect. In this way, a photon can be converted directly into an electric signal and you don’t need humans to create it. «As to what it would sound like, your host star would be constant noise (it’s not emitting any coherent light) and there are enough stars that you’d probably here a constant static coming from them. You’d probably also hear a really loud static coming from everywhere in the universe caused by the Big Bang. If your hearing was really acute, you might be able to pick out the constant sounds coming from pulsars.»

-Orion

As always, we’d like to encourage everyone and anyone to ask us about this stuff. We enjoy it!

astrophysics-unleashed

[astrophysics-unleashed]

Hi another question! (sorry). What textbooks did you use for your planetary science classes? Are there any astrophysics textbooks that you particularly liked? - Zafar

I wasn’t in Planetary so I can’t give you the book we used there (Orion or Dahlek…) 

For me, there’s no one textbook that encompasses the entire subject of astronomy. Instead, there are a bunch of great textbooks that focus on specific branches of the subject. Here are some that stood out for me through college.

Astronomy:

Introduction to Cosmology by Ryden was great. All the other texts I used for astro specifically were alright, but I don’t feel like they were good enough to mention here.

Physics:

Quantum Physics by Townsend.

Anything by Griffiths (he has an E&M book, a particle physics book, and a quantum book).

Thermal Physics by Schroeder (I loved this, I expect my fellow bloggers may disagree).

If you’re looking for some interesting reading that takes you on a journey through the universe I’d also recommend a Brief History of Time by Stephen Hawking.

-DKS

astrophysics-unleashed