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InvisibleDataM
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Re: General Science Thread [Re: figgurate]
    #824175 - 02/27/17 10:24 AM (7 years, 1 month ago)

Quote:

figgurate said:
Why you callin me an asshole?




Quote:

figgurate said:
Literally takes 2 seconds to find out yourself lol.



Quote:

figgurate said:
I helped you and answered your stupid question. You should be thanking me.




Quote:

Data said:
Please keep the dicussion polite




That's why...please feel free to start your own thread if you aren't satisfied with the level of vulgarity in this thread, otherwise keep it polite.

Thanks


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“The Universe is under no obligation to make sense to you” -NDT

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Offlinefiggurate
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Re: General Science Thread [Re: Data]
    #824176 - 02/27/17 10:44 AM (7 years, 1 month ago)

I absolutley agree, you should tell the guy calling people assholes to keep it polite though, not me.

Thanks!

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InvisibleSolar Nexus
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Re: General Science Thread [Re: figgurate] * 2
    #824185 - 02/27/17 04:50 PM (7 years, 30 days ago)

Science is serious business.

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InvisibleStonethM
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Re: General Science Thread [Re: Data]
    #824202 - 02/27/17 11:06 PM (7 years, 30 days ago)

Quote:

Data said:
Quote:

figgurate said:
Why you callin me an asshole?




Quote:

figgurate said:
Literally takes 2 seconds to find out yourself lol.



Quote:

figgurate said:
I helped you and answered your stupid question. You should be thanking me.




Quote:

Data said:
Please keep the dicussion polite




That's why...please feel free to start your own thread if you aren't satisfied with the level of vulgarity in this thread, otherwise keep it polite.

Thanks



QFT!


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:getstoned:

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Offlinefiggurate
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Re: General Science Thread [Re: Stoneth]
    #824215 - 02/28/17 10:52 AM (7 years, 30 days ago)

I still don't see how i'm such an asshole for telling someone it takes 2 seconds to find an answer. I even posted the answer. Where the fuck is my thank you??

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OfflineThebooedocksaint
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Re: General Science Thread [Re: figgurate]
    #824233 - 02/28/17 02:45 PM (7 years, 29 days ago)

I definitely think it would be beneficial if we designed reactors that used some of our excess nuclear waste.

I remember when we talked about nuclear power in my Environmental Chem course, when we talked about nuclear waste disposal, it came up that some countries use, the unstable isotopes we consider waste, for energy generation. (I think france?)


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"Je pense, donc je suis (I am thinking, therefore I am)." -Rene Descartes

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InvisibleDataM
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Re: General Science Thread [Re: Thebooedocksaint] * 1
    #824529 - 03/08/17 07:38 PM (7 years, 21 days ago)

That's true, they're called breeder reactors, or fast neutron reactors.

US fission reactors work by splitting fissile atoms like U-235, which can either spontaneously decay and give off a neutron, or can be actively split by collision with a neutron, releasing multiple neutrons in the process. If the U-235 atoms are packed together close enough such that for each fission event, one of the released neutrons impacts another U-235 atom and causes that atom to split, then the process can go on until the levels of U-235 start to dwindle off. This is called a chain reaction. The neutron population (neutron flux) can be controlled by changing the content of non-fissile neutron absorbers (control rods and boron salts in the water surrounding the nuclear fuel), and thus the reaction rate can be dialed in as designed.

The problem with this setup, is that the reactor core and fuel is designed for thermal neutrons, rather than fast neutrons. The only difference being how fast or how much energy the neutrons have. Fast neutrons are initially released during fission, but are slowed down (moderated) by the water surrounding the fuel. In the process of slowing down, the neutrons give energy (heat) to the water, ultimately producing steam, to drive a turbine/generator to make electricity. The slower moving (thermal) neutrons are also much more effective at only initiating fission, rather than monkeying around with the structure of an atom that it comes into contact with. This whole process is relatively simple, and in the current supply chain environment (cheap uranium ores, and effective methods of enrichment) is the preferred method of producing energy in the US. Its very similar to the obsolete dead dinosaur that we refuse to wean off of, despite the opportunities to develop alternative energy and energy storage solutions. :doublefacepalm:

Anyway, a very small percentage of the fast neutrons leaving the fission site will impact an adjacent U-238 atom (US nuclear fuel is regulated to less and 5% fissile U-235) or some of the steel support structure. Fast neutrons have enough energy to change the isotope of the adjacent material, and over time, these increasingly unstable isotopes will decay into other elements that are also radioactive and potentially fissile. In the US, we consider that too difficult to control with our current plants, and public relations has all but killed the drive to build any new reactors...thus the new radioactive and fissile material is labelled nuclear waste, and put into special storage to waste energy for years to come.

Nevertheless, this generation of "waste" is exactly what fast neutron reactors take advantage of. They sacrifice more of the available neutron flux to convert non-fissile material into fissile material, at a rate that is faster than the burning of pre-existing fissile material. While this may just seem like they are just moving energy around, what this actually does is to reposition existing energy in the non-fissile material.

Consider it like this, U-238 is non-fissile, and thus cannot be used for energy production. However, U-238 atoms have a ton of pre-existing energy bound up in their nucleus that just can't be accessed currently, because the atom is simply too stable. By adding a few neutrons, and letting a high-neutron uranium isotope decay into a higher proton atom like plutonium, the overly stable atom becomes a much less stable atom that is ready to pop. The input of energy from the neutrons is vastly outweighed by the energy output of the resulting fission event, and the breeder reactor can still produce some usable electricity while it is running. :awecid:

I agree with boondocks on this one, we need to start re-developing breeder reactors in place of our old clunky thermal neutron reactors. It would provide a method for utilizing a good portion of radioactive waste for energy, and whats left over is just a fraction of what you started out with.  The problem at this point is the general public's opinion on nuclear in general. There is a lot of misinformation about nuclear floating around, and its difficult for people to wrap their brains around the scientific background needed to understand the actual risks vs. the perceived risks.

Sorry for the delay on the answer, been super busy lately :shrug:


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“The Universe is under no obligation to make sense to you” -NDT

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Invisibledrawde
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Re: General Science Thread [Re: Data]
    #824555 - 03/09/17 06:14 PM (7 years, 20 days ago)

I've been reading about redshift and trying to understand what causes the increase in wavelength.
Most sources just describe how the position causes the Doppler effect, but I want to know why it is that EMR can increase λ and necessarily decrease in energy moving through space and where the energy goes.


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King Koopa said:
The amount of pot that Gask smokes is equivalent to a guy shooting heroin on weekends

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InvisibleDataM
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Re: General Science Thread [Re: drawde]
    #824560 - 03/10/17 09:15 AM (7 years, 20 days ago)

So, I'll try to explain the sources of redshift/blueshift in terms of how I understand it (simplified examples that make it easier to grasp, because my mind is small). When you get down to the quantum explanation, this may not be the complete story, because to be honest I don't understand the nature of subatomic particles completely. :shrug:

As you've stated, red shift can occur when the emitting source is moving away from the observer. The EMR waves can only propogate at the speed of light, and the emitting source is emitting waves at a fixed interval (the initial frequency), and so the waves peaks are spatially emitted further apart from each other, resulting in a longer wavelength (lower frequency) of the emitted EMR. Because they are spatially stretched out (the emitting source has moved further out from the observer at the end of the emission than it was when it began emitting), the observer will see a redshifted source of EMR whose duration is slightly longer than the duration of emission of the initial EMR as measured at the source. The total energy emitted is the same as the total energy observed, but its more spread out.

Same thing occurs with the redshift of light as it travels long distances across the universe. This redshift is the combined result of the redshift due to relative motion between the source and the observer, and the expansion of spacetime between the source and the observer. If one imagines the expansion of spacetime as the stretching of a rubber sheet, i.e. space is expanding in all locations at once, rather than from a particular source, then this means that an EMR wave will also spatially expand as it propagates through the vacuum of space. This will result in the stretching of the waveform, a lengthening of the wavelength, and a spreading out of the total energy of the wave, thus resulting in a wave that is "lower energy", but will strike the observer for a longer period of time. This is how the energy stays conserved, but has a "lower energy" wave. Blueshift works the same way, but just concentrates energy and shortens observed duration.

Now, if you want to, we can get into the relativity portion of this, where you have to take into account that light has to be travelling at the speed of light relative to any observer at all times, and thus time dilation plays the primary role in modifying the apparent waveform and duration. But I'll have to pull out some paper and draw some pictures, and it'll take me a hot minute to make sure I've got everything pinned down. :ancientaliens: I'll let you make the call on that bucket of worms.

So basically, redshift/blueshift is the process of diluting/concentrating EM wave energy across spacetime, and energy is conserved by increasing/decreasing the duration of the total emission (thus truly stretching/compressing the emission through all 4 dimensions of spacetime), respectively.

Feel free to ask questions about this, I'll try to explain it as best I can. Its definitely a confusing topic...I kept having to stop and re-read what I was typing to make sure it actually made sense  :awkwardconfusion:


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“The Universe is under no obligation to make sense to you” -NDT

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Invisibledrawde
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Re: General Science Thread [Re: Data]
    #824561 - 03/10/17 10:06 AM (7 years, 20 days ago)

That makes perfect sense. Idk why physics can't get some people who can explain shit in a coherent manner.
I'd love to hear more about how relativity plays a role if you care to get into it. Up2u.


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King Koopa said:
The amount of pot that Gask smokes is equivalent to a guy shooting heroin on weekends

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InvisibleDataM
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Re: General Science Thread [Re: drawde]
    #824721 - 03/14/17 07:03 PM (7 years, 15 days ago)

I promise I'll get around to answering the last question...I just need to find a spare hour or so to write up the explanation. I'll definitely have some time on Friday if I can't get to it earlier :gethigh:


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“The Universe is under no obligation to make sense to you” -NDT

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Invisibledrawde
Registered: 11/15/09
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Re: General Science Thread [Re: Data]
    #824722 - 03/14/17 07:49 PM (7 years, 15 days ago)

You have better shit to do my man. I'll just continue trying to decipher my cosmology book.


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King Koopa said:
The amount of pot that Gask smokes is equivalent to a guy shooting heroin on weekends

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OfflineTrueHerbCrystal
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Re: General Science Thread [Re: Data]
    #824758 - 03/15/17 09:49 AM (7 years, 15 days ago)

I got a question (for Data and not figgurate):

Why does metal glow red when its really hot?

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Invisibledrawde
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Re: General Science Thread [Re: TrueHerbCrystal] * 1
    #824762 - 03/15/17 11:04 AM (7 years, 15 days ago)

So red, or any other color we see is a wavelength of electromagnetic radiation. All bodies (objects, matter) above absolute zero emit electromagnetic radiation at all wavelengths. The higher the temperature of the body the greater the intensity of the EM radiation at certain wavelengths (depends on the material). So when metal is so hot that it is glowing red, there is enough heat energy to emit a significant portion of EM radiation in the visible region of the EM spectrum, and most of it is the wavelengths that correspond to the color our eye/brain system recognizes as red.


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King Koopa said:
The amount of pot that Gask smokes is equivalent to a guy shooting heroin on weekends

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InvisibleDataM
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Re: General Science Thread [Re: drawde] * 1
    #824767 - 03/15/17 02:14 PM (7 years, 14 days ago)

Drawde hit the nail on the head.

This radiation can be described by Planck's Law, which is broken up into the more practical Stefan-Boltzmann Law (total energy emitted by an object based on its absolute temperature), and both the Rayleigh-Jeans Law and Wien Approximation (peak-intensity frequency of the EM spectra emitted by the object as a function of absolute temperature, for low and high requencies, respectively).

For trivia purposes, the temperature at which all object visibly glow due to this EM radiation is called the Draper Point, and is established at 977 degrees F :awecid:


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“The Universe is under no obligation to make sense to you” -NDT

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OfflineThebooedocksaint
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Re: General Science Thread [Re: Data] * 1
    #824768 - 03/15/17 02:48 PM (7 years, 14 days ago)

On a related note, thin section petrographic microscopes are awesome and have some real light shenanigans going on. Are you familiar with them at all? If not I would be happy to explain some of the crazy things you do to identify what minerals you're looking at. If anyone is interested in hearing just speak up. Pics related.

I only really have used them in a mineralogy course though, so there could be some things I don't have any clue about what could be in a petrology course.







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"Je pense, donc je suis (I am thinking, therefore I am)." -Rene Descartes

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Invisibledrawde
Registered: 11/15/09
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Re: General Science Thread [Re: Thebooedocksaint]
    #824776 - 03/15/17 05:01 PM (7 years, 14 days ago)

:ohwow:

Quote:

Thebooedocksaint said:
If anyone is interested in hearing just speak up





Yes please!


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King Koopa said:
The amount of pot that Gask smokes is equivalent to a guy shooting heroin on weekends

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OfflineTrueHerbCrystal
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Re: General Science Thread [Re: Data]
    #824800 - 03/15/17 11:15 PM (7 years, 14 days ago)

Amazing!

Thanks guys :popcorn:

Another light question: todays movies are digital. How are digital movies projected so bright onto the screen?

I know the old way was film with a huge HPS bulb behind it.

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InvisibleDataM
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Re: General Science Thread [Re: TrueHerbCrystal] * 1
    #824874 - 03/17/17 08:24 PM (7 years, 12 days ago)

So I'm about to double-post, there is a whopper of a relativity post coming up.  :docbrown:

Most theatrical projectors use Digital Light Processing (DLP).

The heart of a DLP projector lies in its 1 or 3 (or more) Digital Micromirror Devices (DMDs) which are essentially semiconductor chips with large arrays of tiny (5 micrometers, or 0.0002 inches) mirrors mounted on a swivel, and individually controlled by incredibly fast-acting electrostatic actuators to toggle the path of an incoming light beam to either the screen (through a series of optics) and appear bright, or to a light absorber and heatsink (in order to not let the light onto the screen) and appear dark.

Each micromirror can function as a single pixel (or sometimes 2 pixels if the mirrors are designed to work fast in multiple directions), and by varying the amount of time that the mirror points toward the screen vs. away from the screen, can vary the apparent brighness of that pixel.

The color control comes from one of 2 schemes. The first involves the projector having 3 seperate DMDs, each controlling the pixel field for either reds, greens, or blues (the light color is provided by 3 seperate red, green, and blue light sources), and each of the 3 images formed is combined into the full color image through the optics of the projector. The second way to do this is by using a single extremely fast DMD, and using a single light source with a spinning color wheel between the light and the DMD, to quickly alternate between red, green, and blue source light while the DMD quickly switches through the respective red, green, and blue pixel fields. This switching occurs so fast on the projector screen that our eyes can't distinguish the individual color pixel fields...and so all three blur together to form a single full-color image.

This technology was used in big-screen TVs a while back, but has since been replaced as LCDs and OLEDs began to get cheaper to build on that scale. However, since it would still cost way to much to build an LCD or OLED display the size of a theater screen, and because DLPs provide a way to brightly project digital formats...they are still used in theaters today.


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“The Universe is under no obligation to make sense to you” -NDT

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InvisibleDataM
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Re: General Science Thread [Re: Data] * 1
    #824877 - 03/17/17 09:05 PM (7 years, 12 days ago)

Drawde, this is for you dawg :bobmarley:


So before we get started into any kind of time dilation discussion or relativity, I'm going to explain a little background on the subject that will make the explanation a little easier to understand. I realize that you may already know this stuff, so I'm going to label each topic or definition, and end the introduction section with a line of asterisks so that you can TL:DR the shit out of it if you so choose.

Vectors - Vectors are simply a mathematical way to describe something like a change in displacement, velocity (speed and direction), acceleration, jerk, jounce, etc. A vector can describe these characteristics in any number of dimensions, because its nothing more than a convenient way to describe something and do math with that something.
So for our discussion, we'll only need to know about 3-vectors and 4-vectors, with the number indicating the number of dimensions (or components) that make up the total vector. The 3-vector will make the most sense, as it describes properties of an object in terms of the 3-spatial dimensions (length, width, height...or x, y, and z).



In this picture, the 3-vector is named "a", and each component of the vector are labeled "ax", "ay", and "az", which you'll notice only describe the length, width, and height (respectively) of the vector as it projects out from the origin (or central corner) of the plot. In equation form, this vector can be written as:  a = ax + ay + az. Note that we just use this as a way to tell the reader how many dimensions the vector consists of, and what the individual values of the components of the vectors are. While it can be used for mathematical purposes, we won’t be doing anything with it. If you’d like a better explanation of this, please feel free to ask for a later post.

The reason we use these to describe physical qualities of an object is because in this configuration, the values of a, ax, ay, and az are all mathematically related, and one only needs to know basic trigonometry in order to calculate these values. For instance, if we know the general direction of the object (the ratios between ax, ay, and az), and we also know the actual value of ax, then we can compute the entirety of ax, ay, az, and a. In another example, if we know ax, ay, az (and thus a)...and any one of the x,y, or z components changes, but the length of a stays the same, then we can re-calculate what the new x and y components will have to be.

A 4-vector is no different, other than it has another component to it. When used in a real example, it describes characteristics of an object in the 3 spatial dimensions as well as through time, which is treated as the 4th dimension. This is impossible to draw, but can be represented by an extremely simplified drawing. We can take the 3 spatial dimensions and find the combined magnitude of them by using an extension of the Pythagorean theorem, or that for a right triangle seen below, C^2 = A^2 + B^2…which can be worked out to C = SQRT(A^2 + B^2)



Now, if we look back to the first figure, under the explanation of vectors, we can see that you can form right triangles that can be used to easily calculated the length of vector a from each of the components (see below).



Notice the first right triangle formed by ax, ay, and the purple hypotenuse (the longest side). The 2nd right triangle is formed by the purple hypotenuse of the first triangle, az, and vector a as the final hypotenuse. If we apply Pythagorean’s theorem to the first triangle we get

(Purple hyp)^2 = ax^2 + ay^2

And if we do the same thing for the 2nd triangle we get

A^2 = (purple hyp)^2 + az^2

And since the right side of the first equation can be substituted into the 2nd equation for (purple hyp)^2, we can finally get

A^2 = ax^2 + ay^2 + az^2
Or
A = SQRT ( ax^2 + ay^2 + az^2)

Using the last equation, we can calculate the total length of vector a from its individual components, which allows us to condense 3 dimensions into a single number, which will come in handy later.


Relative Velocity - Relative velocity is pretty simple, but requires an explanation of fact in order to appreciate the significance of its universal application.

Assuming that the universe, is filled with an apparently infinite (or boundless, as far as we can tell) expanse of nothing (vacuum), the 4 fundamental fields, and their perturbations (the wavy static in the fields that give rise to all of the matter and particles in the universe), and that all of these particles are all moving, it is plain to see that there is no eternally static reference point that we can use to determine an absolute velocity. Therefore, the only velocity information we can gain about an object must be a relative velocity, which is the velocity of an object relative to the observer. When determining the relative velocity of an object, we assume that the observer is not moving, even if they might be compared to another observer nearby. In reality, all observers may be moving relative to each other and everything else in the universe, but this gets hella confusing, so in order to simplify each observation, we assume that the observer is stationary, and determine the relative velocity of the observed object based on that assumption.

As an everyday example, we can think about ourselves driving on the freeway. If we are driving towards an overpass, we usually think of this situation in that we are the ones moving toward the overpass at the speed thats currently on the speedometer (lets just say 70mph in this example). In this case, we are actually describing the relative velocity of the car with respect to the overpass (and thus the surface of the earth, which the overpass is attached to, which we measure through the wheels). We could just as easily think of it as we are stationary, and the overpass is moving toward us at 70mph (and the earth's surface is moving under us at 70mph). If we consider another car that is passing us, and his speedometer measures 75mph relative to the earth and overpass, we could also consider ourselves stationary and his velocity as 5mph relative to us, or even as him being stationary and our velocity as -5mph relative to him. In fact, we are moving at 70mph relative to the earth's surface, which is moving at roughly 1000mph relative to the center of the planet, which is moving at about 70,000mph relative to the sun, which is moving at about 450,000mph relative to the center of the Milky Way galaxy, which is moving at about 250,000mph relative to our neighbor the Andromeda Galaxy...hence the need to set up a "stationary" reference point that makes sense when thinking about certain scenarios. This is why we use the term "relative velocity", and we'll get back to this concept later.


Frame of Reference - This is an extension from relative velocity. The frame of reference (aka the inertial reference frame) is just a fancy term that adequately describes the stationary observer we just talked about. Keep in mind that for the same example, the frame of reference can be changed multiple times, in order to look at the example from multiple viewpoints that are all relative to each other. You'll see this happen in the explanation quite a lot.


Relativity - Is just the general concept that all observations made of an object or event in our universe is relative to the observer (the frame of reference). This means that the same event or object may appear to occur slightly differently between two observers, which will ultimately mathematically and logically work out to being the same event. This is purely a consequence of the fixed speed limit of light, and the vast size of the universe, as the transmission of information (and thus perception of an event) is physically limited by the universal speed limit. It may not make sense now, but once the 4-vector is explained, it will start to make a lot more sense.

*************************************************************************

C, the universal speed limit – So the most important concept to get down when discussing the relativistic Doppler effect is that of time dilation, specifically time dilation that arises from the relative velocity between two objects. This is where the knowledge of vectors and trigonometry becomes handy.

So, the speed of light in a vacuum (usually denoted ‘c’), 3x10^8 meters per second is widely known as the universal speed limit, and we now know that all objects move through space-time at the speed of light.  While we usually think of this in terms of the 3 spatial dimensions, in reality this speed and its limit applies across the whole of space-time…meaning that the rate of passage of time is also tied to this speed and its limit.

Lets get into an example. Think of an object flying through empty space past us. We’ll use a 4-vector to describe its relative velocity to us, and we’ll call the vector A.

A = Ax + Ay + Az + At

Where Ax,y,z are the 3 spatial dimensions (what we normally think of as spatial velocity), and At is the velocity of the object through time (or how fast the object is traveling into the future).

Now, if we refer back to the method described in the introduction on how to condense the 3 spatial components into 1 single value (which we’ll call As for the speed of vector A), we can reduce the vector to the following:

A = As + At

Where:

As = SQRT (Ax + Ay+ Az)

So, now that we’ve simplified the 4-vector into something we can plot on a graph, we can get into the effect of time dilation.



The figure above shows us what we are now working with. We have calculated As, but we aren’t sure about At yet. So we need to know what the values are for both A and As in order to figure out what At is. Well, because the universal space-time speed limit is c, and all objects move through space-time at c, we now have a fixed value that we can plug into the final value of A:

A = SQRT (As^2 + At^2)

Becomes

C = SQRT (As^2 + At^2)

Or

C^2 = As^2 + At^2

And finally, by moving the As component to the same side as the C component:

At = SQRT (C^2 – As^2)

Now, as you can see, C is a fixed value, so At only varies as As varies, and you can also see that when As is small or zero, At is maximized towards the value of C. Also, as As gets large (approaches or equals C), At will get smaller and smaller, trending towards zero. What this ultimately means in the real world is that as relative speed through the 3 spatial dimensions increases, the relative passage of time of that object slows down. This effect is known as Time Dilation, and it’s important to remember that this effect is relative, as in its effect will depend on the frame of reference of the observer.

To explain, let’s go back to the example of the object flying past you in empty space. In this frame of reference, if you had a clock with you, and there was also a clock on the object flying past you…then you would see that the clock on the object would be moving slower than the clock you hold in your hand. If you rewind to the beginning of the example, but switch up the frame of reference so that you are riding on the object through space, and your original clock was left in your original frame of reference, then it would appear to you now that you are standing on a stationary object, and your original clock is flying past you in the opposite direction. Thus, your original clock would now be the one experiencing time dilation and would be running slower compared to the clock you are looking at on the object.


Light always moves at c, sorta – So now we have to discuss the rules of light, and their own relativity. The simple rule is that light (photons) travel at the speed of light C, relative to the frame of reference. What this means, is that from an observer’s frame of reference, all light coming/going to/from the observer are travelling at speed c.

As an example, consider 2 objects travelling away from each other with relative velocity ‘v’. If we are standing on object 1 (the current frame of reference), then to you, object 1 is stationary, and object 2 is moving away from you at velocity v. Let’s ignore time dilation for a minute, and focus purely on light. If we could see photons that are leaving us, and shine a laser towards object 2, then the photons leaving the laser would appear to us to leave object 1 at velocity c, and would travel towards object 2 at velocity (c – v), relative to object 2. However, if one were to rewind this example, and swap locations so that we are now standing on object 2, and left the laser beaming towards us from object 1, then it would appear to us that object 2 is stationary, and object 1 is moving away from us at velocity v, and the photons from the laser are arriving on object 2 at velocity c, but leaving object 1 at a velocity of (c + v), relative to object 1.


Now we put it all together – Now that we have the relative nature of light’s apparent relative velocity, and the relative nature of the passage of time as a relation of an objects relative velocity…we can put together an example of relativistic Doppler effect, or the redshift/blueshift phenomena.



Consider 2 objects in the following several cases, object 1 will be the emitter of light (designated by p for photon), and object 2 will be the receiver of light. This will remain constant throughout all cases. Also, one must assume that you can see photons in all cases, which doesn’t always happen in reality, because the only photons you see are the ones that hit your retina.


Case 1:
In this case, the frame of reference is from the surface of object 2, looking toward object 1. From our reference frame, object 1 is moving away from us with velocity v1. A beam of light leaves the surface of object 1. The initial frequency of the light at object 1 is 510 terahertz (THz), or 510 trillion waves of light generated per second, heading toward object 2 (yellow light, wavelength of about 588 nm).

So, from the reference point of object 2, the light waves must be travelling at c relative to object 2. We first see the time dilation effect on object 1 as a result of the relative velocity, so time appears to move more slowly on object 1, which reduces the frequency of the generated light (thus slightly redshifting the beam of light prior to it leaving the object to say something like 500 THz (which would require that the velocity be something on the order of 0.2c, or about 132 million mph).

But, at the same time, the waves of light also appear to the observer to be leaving object 1 with a velocity of c + v1, since that would be necessary in order for the waves to be arriving at the observer at velocity c. So, one wave has had a chance to travel 1.2 times the distance that it would normally travel at velocity c before another wave was emitted from the source, and so the wavelength increases by 1.2 times the already time-dilated wave leaving object 1. This further stretches the wavelength from 600nm @ 500 THz to 720nm, which works out to about 417 THz. Thus, the total redshift of the light coming from object 1 to the observer on object 2 is an increase in wavelength from 588nm (yellow light) to 720nm (deep red).


Case 2:
In this case, the frame of reference is still from the surface of object 2, looking toward object 1. The difference is that the velocity is reversed, and object 1 appears to be moving toward us at velocity v1, which we’ll keep at 0.2c just to see how it affects the relative blueshift.

So we get the same amount of time dilation on object 1, so our initial 510 THz (588nm) beam of light lengthens out to 500 THz (600nm). The difference now is that the apparent velocity of the beam of light from the surface of object one is c – v1 instead of c + v1. What this means is that each wave of light only travels 0.8 times the normal distance it would travel before another wave is emitted, effectively shortening the final wavelength to 0.8 times that of the already time-dilated beam. This results in a total change in wavelength from 588nm (yellow) to 480nm (light blue to teal).


Case 3 and 4:
It should now be apparent that if we reverse the frame of reference to object 1, and watch for the relative time dilation of object 2, and combine it with the apparent late and early arrival times for the light waves for the case of object 2 moving away and towards object 1, respectively….that the redshift/blueshift phenomena are in agreement between both the reference frame of the source and the reference frame of the receiver. However, to observers in either reference frame, the physics of their local area (their reference frame) never changes, but rather the far away objects in relative motion to the observer is the only thing changing or acting strange. It should also be noted that in the case of relativistic Doppler effects, the relativistic portion acts to both allow the normal Doppler Effect to happen while also maintaining the constant speed of light relative to the local reference frame. Additionally, relativistic time dilation acts to both accentuate the redshift of an observed object moving away from the observer, while conversely reducing the blueshift from an observed object moving towards the observer.

Thus, our funky journey through a small amount of relativity comes to a conclusion. Feel free to ask any questions you want…but I can’t necessarily guarantee that I will be able to answer them. :pipesmoke:


--------------------
“The Universe is under no obligation to make sense to you” -NDT

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