**Ask a monkey a physics question thread**

[MadMojoMonkey]

I don't promise to be right, but I will do my best to answer any physics related questions.

[bikes]

How does one accidentally a coca cola?

[Chelle]

Pretty sure I could find a video.

[bikes]

Also is there an alternate universe in which I am currently banging Alison Brie?

Also will the universe Big Crunch and then Big Bang the same way on to infinitude and as such have we lived this life an infinite amount of times and will live it again an infinite amount of times?

[MadMojoMonkey]

How does one accidentally a coca cola?

non physics answer:

coca cola means "biting the wax tadpole" in Mandarin Chinese.

Clearly you mistook the wax one for the real one.

[MadMojoMonkey]

Also is there an alternate universe in which I am currently banging Alison Brie?

Physics answer: Not my problem.
Physics deals with observables, and any alternate universe, by definition, is unobservable. As the universe is anything which has been observed, and an alternate to being observed is NOT being observed.
Non-physics answer: In an infinite multiverse, anything is possible.

Also will the universe Big Crunch and then Big Bang the same way on to infinitude and as such have we lived this life an infinite amount of times and will live it again an infinite amount of times?

Physics answer: still collecting data
The current evidence for the existences of dark matter and dark energy is astounding. These terms are blanket terms used to describe matter and energy which have a visible affect on the structure of the universe, but have not been directly detected yet. In short, we know that we don't know what 90% of the universe is made up of, so speculating on long term evolution involves a huge number of assumptions. It may become good science, but it's not good science yet.

Non-physics answer:
As for a repeating universe that keeps happening over and over... well I think I can safely speculate that the Heisenberg Uncertainty Principle will prevent duplications. Of course, I'm now speculating what happens when the laws of physics break down into a singularity and then reform in expansion... so no science there.

[a500lbgorilla]

Which tool has yielded the greatest amount of physics related discovery?

I mean physical tool like a straight edge, or a telescope not thinking tool like math, or the theory of electromagnetism.

[JKDS]

How would you describe what finding the Higgs Boson means to a 3rd grader?

[MadMojoMonkey]

Which tool has yielded the greatest amount of physics related discovery?

I mean physical tool like a straight edge, or a telescope not thinking tool like math, or the theory of electromagnetism.

One answer: pen/pencil/chalk/scribe

Basically, the tool which allows ideas to be written down. This opens up the door for longer, more developed ideas and the ability to share ideas with others.

Another answer: lens

It was the use of lenses that allowed Galileo to first observe the sky with a telescope. So many advances in medicine came from understanding the microscopic world.

Yet another answer: computer

Is a computer a single tool or many? Either way, we got all the way to Quantum Mechanics and Theory of Relativity without them. It must be noted that while computers have not been around for very long in the world of physics, they are an essential tool to every modern physicist.

My final answer: the human mind

Bazinga.

[Stacks]

How would you describe what finding the Higgs Boson means to a 3rd grader?

Fuck that. Explain it to me like I'm 5.

[MadMojoMonkey]

How would you describe what finding the Higgs Boson means to a 3rd grader?

First you find something, then you try to figure out what it is.

Don't put that in your mouth! OK.

So some scientists did a big experiment and they were looking for something and they found it.

No, they didn't find any trucks. Let go of my leg. Sit in your chair.
No, they didn't find any pizza or princess-footballs (???) either.
No, none of that stuff.

They don't even know. Well, they know it's not a truck or a pizza. Verdict's still out on the princess-football.

They found a tiny, tiny thing. It was so small, they weren't even sure they saw it at first. But they kept looking and looking and they found it.

Now they are going to try to figure out what it is they found.

Lets all go outside and look for something very tiny and then figure out what it is we found.


EDIT: *note: I haven't been exposed to 3rd graders in ages; this may be the kindergarten version.
RE-EDIT: So how'd I do, stacks?

[OngBonga]

What shape is the universe?

[MadMojoMonkey]

3rd grade version, 2nd attempt.

OK, so there's all these theories in physics and mostly they work together like a charm. Not everywhere, though. The current theories of electricity and what a layman would call "nuclear radiation processes" are our example. Both work well on their own, but when joined, the math says that particles should have no mass. The theories are compatible except in this respect and they work extremely well on their own. Something's missing.

If you try to manipulate the existing theories to "get" particles to have mass, something always gets broken. I mean, something that makes even less sense comes up in the theory, and it comes up all over the place.

The missing thing is called the Higgs Mechanism, the process by which particles acquire mass. It's a theory from the 1960's by a guy named Higgs. He wasn't the only one who came up with it. He was working with partners, but that's not what I mean. I mean 3 papers from 3 different countries were published at the same time with the same theory. It was there to be guessed.

So. the Higgs mechanism states there is a field (just like an electric field) that particles interact with. Let's call it the Higgs field. By interacting with the Higgs field, particles acquire mass.
How do the particles interact with the Higgs field? What particle in the Higgs field do they interact with?
Why, the Higgs boson is what we'll call the new particle.

The theory says there should be a particle that is extremely unstable (it decays into other particles in much less than 1 second), that can be detected in very high energy collisions, like the collisions in particle accelerators.

It took years of building a big enough particle accelerator to make a high enough energy collision to have any hope of detecting a Higgs boson. The LHC at CERN has accomplished this task. After more years of experimenting, scientists have found a particle with some of the properties that Higgs suggested the Higgs particle should have.

So there you have it. The Higgs boson has been found. Now we can study it in further experiments at higher energies and, hopefully, neatly tie 2 separate theories into 1.

[MadMojoMonkey]

What shape is the universe?

Definition: the universe is anything which has been observed by humanity, and anything which can be realistically observed by humanity in the future.

According to the information gathered by COBE, the cosmic microwave background radiation is (broadly) homogeneous in all directions, at a distance of ~13.7 billion light years in all directions. This was predicted to be the case by quantum theory and big bang cosmology. Theory motivated a search and the search yielded the prediction. This is sound science.

Our event horizon... the edge of humanity's observable universe is a sphere around us that is ~13.7 billion light years away

[wufwugy]

was nikola tesla legit

[MadMojoMonkey]

was nikola tesla legit

He was a brilliant scientist. He was no good at making friends. There is some speculation that he had Asperger Syndrome, due to his extremes in both of these.

His primary flaw was becoming overly obsessed with ideas that didn't yield anything. Great scientist, poor technologist.

[wufwugy]

some people think tesla was the greatest inventor of all time, and i have no idea how much of the stuff is just myth. what did he truly invent, and what, if anything, did he find that modern physics hasn't (im sure that's just part of the myth though)?

[jackvance]

Explain the theoretical basis for time travel.

[MadMojoMonkey]

Really?
Nicola Tesla's very well hidden web page

[rong]

Are we inside a black hole?
This seems to me to be the most obvious explanation of our universe.
Is there any evidence to suggest we aren't?

[MadMojoMonkey]

Explain the theoretical basis for time travel.

First thing in the morning. Otherwise I phone this one in, too.

[JKDS]

Neil Degrasse Tyson: Great scientist? Or Greatest Scientist?

[wufwugy]

Really?
Nicola Tesla's very well hidden web page

thats some colin powell shit

that i was going to eventually decide on reading

but you said you wanted some questions

[wufwugy]

Explain the theoretical basis for time travel.

answer

there is none

[JKDS]

Time isnt even a thing! There is no time! NO TIME FOR ANYONE

Dec 2012

[kiwiMark]

Which tool has yielded the greatest amount of physics related discovery?

Newton used to give people locks of his hair as gifts if that qualifies him.

[givememyleg]

is it possible for the seemingly stable laws of physics that guide our universe to change over time? do the laws that we observe today differ from the laws that existed 1 billion years ago? 10 billion? 1 hour after the big bang?

[OngBonga]

answer

there is none

Incorrect. In theory, it's pretty easy to travel into the future. Going back in time is quite probably impossible, but forwards... it's just a matter of moving very fast.

Let's put our science man to the test, since I absolutely can't argue with his response on the shape of the universe, even though I don't think humans are anywhere near knowing for sure...



If I'm travelling at half the speed of light, how much time does it take me to travel a light year?

[MadMojoMonkey]

Explain the theoretical basis for time travel.

The important thing to remember is that the flow of time is relative. If you start with 2 perfectly synchronized clocks and hold one of them still, while the other one is moved through some path, and then brought back together with the first clock, they will not necessarily be synchronized anymore. Clocks in different gravitational fields will tick at different rates. Clocks moving at different speeds will tick at different rates. This sounds like total BS to the uninitiated, but it is solid physics. In fact, GPS and many other technologies would not work if not for the implementation of this knowledge.

A train moving at a constant velocity passes a train station. A person at the station sees themselves standing still and the train moving away. A person on the train sees the train standing still and the platform moving away. Both descriptions are perfectly valid and do not contradict each other, because motion is relative to a reference frame, and any inertial reference frame is equally valid to any other (Newton's 1st).

But what you're really asking is can you time-travel like in science fiction? Short answer is: forward. You can alter the rate at which you travel forward through time by traveling near the speed of light, and to a smaller extent by spending time in a different gravitational field. People who live on mountains actually live ~0.003 seconds longer over their lives due to the slight decrease in gravity.

That's how it would look to the person on the coast, anyway. To you, your clock is in the same field as you, moving at the same rate as you, so as far as you're concerned, it's THEIR clocks that are ticking too slowly. Your clock will always look normal to you, as long as you are in the same reference frame.

Theoretically, when 2 black holes collide, there are closed orbits in which something could actually collide with itself, illustrating the extreme warping of space-time that occurs near intense gravitational fields.

[MadMojoMonkey]

Are we inside a black hole?
This seems to me to be the most obvious explanation of our universe.
Is there any evidence to suggest we aren't?

Physics answer: could be
Nothing can be observed beyond an event horizon, and therefore it is outside the purview of physics. We don't know what happens inside black holes, so it is impossible to rule out that the entire universe is, in fact, inside a black hole.

As stated, there can be no physical evidence for or against this claim.

[MadMojoMonkey]

Neil Degrasse Tyson: Great scientist? Or Greatest Scientist?

He's my favorite ambassador to science. I must confess that I haven't read any of his publications, so I can not judge his scientific credentials. My guess is that he's a great scientist.

The competition for Greatest Scientist is pretty damn tough, and I'd guess that Niel doesn't actually spend much time experimenting.

[jyms]

I want to know what the general belief is of what's on the other side of the universe as it expands out. I can't seem to picture nothing, as nothing like we have in space is something. So what is the something our universe is expanding into as it becomes the universe, what is the part that is shrinking?

[MadMojoMonkey]

thats some colin powell shit

that i was going to eventually decide on reading

but you said you wanted some questions

I'm sorry. I was fall-over tired and I'm coming down with a cold, so my patience was at it's thinnest. I did realize that I phoned that one in, as I stated in a later post. Sorry if I let you down.

There's a lot of mystique around Nicola Tesla. I don't know what his actual contributions to physics are, except that he was jointly nominated for a Nobel Prize along with Edison, that they did not win. I don't know what work they did that attracted the attention of the Nobel committee. The Nobel Prize is awarded for a specific experiment or publication, it's not a lifetime achievement award.

If there is anything that he discovered that is NOT a part of the Standard Model, it would have to be well hidden and secret to the point that you or I would never know about it. I find this unlikely, as he died in 1943, before the rise of computers and the huge advances in the Standard Model over the past 70 years.

[OngBonga]

Nothing can be observed beyond an event horizon

This interests me a great deal. I'm not convinced it's 100% true. For example, let's say you're inside a black hole, and it nearly collides with another. Can you know there is another black hole beyond your event horizon? Well, actually, yes, I think so, because each black hole effects the spin of the other. This is how black holes slowly lose their energy, according to my understanding (which may well be very flawed) of Hawkins' ideas. If you can see that your black hole is losing x amount of spin at x rate, you might be able to determine that your black hole is close to another black hole.

Of course, I have no idea if this is true. It's just my interpretation of Hawkins' ideas. But it demonstrates, to me, that the concept we cannot observe beyond an event horizon is perhaps flawed.

[MadMojoMonkey]

is it possible for the seemingly stable laws of physics that guide our universe to change over time?

Depends what you mean. If the laws of physics don't adequately describe the observed universe, then they are updated. Unlike some institutions, when a statement made by physics is disproved, it is discarded.

At this point in the quest of physics, not much gets discarded, a lot gets tweaked. The Standard Model works so well on so many levels that it's far more likely that the statements are nearly correct than completely wrong.

do the laws that we observe today differ from the laws that existed 1 billion years ago? 10 billion? 1 hour after the big bang?

No. No. and No. (Well, replace those with almost definitely no, as there are no certainties in science.)

The Standard Model describes the universe starting ~10^(-40) seconds after the big bang until now. That's
0.000 000 000 000 000 000 000 000 000 000 000 000 000 1 seconds.

[MadMojoMonkey]

Let's put our science man to the test, since I absolutely can't argue with his response on the shape of the universe, even though I don't think humans are anywhere near knowing for sure...

How'd I do?

If I'm traveling at half the speed of light, how much time does it take me to travel a light year?

ASSUMPTIONS:
1) you travel at a constant velocity throughout
2) you travel in a straight line
3) the path of travel is 1 ly (light year) in length to a stationary observer

The first thing we need is the relativistic gamma factor.
gamma = 1/SQRT(1-beta^2)
where beta is the fraction of the speed of light of the traveler (here 1/2)
gamma = 1/SQRT(1-(1/2)^2) = 1/SQRT(1-1/4) = 1/SQRT(3/4) = 2/SQRT(3)
gamma ~= 1.154

Now, we need to answer this in 2 meaningful reference frames: the traveler (you) and a stationary observer from the point of your journey's origin (me). We each have a reference sphere, just 'cause we're clever like that.

In your reference frame, your clock ticks normal and my clock ticks slow. Your sphere looks normal, but my sphere looks slightly pancaked. In my reference frame the exact opposite is true. My clock and sphere are normal, and yours are the ones that are distorted. Specifically, we see each others clocks are ticking 1.154 times too slow, and that each others spheres are 1.154 times shorter across the diameter parallel to the direction of your ship's travel.

In your reference frame, the distance you are traveling is LESS THAN 1 light year, since it's not just my sphere that's pancaked, it's the entire universe outside of your ship that's pancaked.
Your perceived distance to travel is 1 ly/1.154 = 0.866 ly.
Your perceived travel time is 0.866 ly/(1/2 ly/years) = 1.73 years

I see your pancaked ship travel a distance of 1 ly and it takes you 2 years to get there.

During your journey, you aged ~1 year and 9 months, while I aged 2 years. Does this count as time travel?

[MadMojoMonkey]

I want to know what the general belief is of what's on the other side of the universe as it expands out. I can't seem to picture nothing, as nothing like we have in space is something.

Anything which can not be observed is outside the purview of physics.

Time and again as a physics student I was reminded whether or not I can visualize a phenomenon does not correlate to the existence of said phenomenon. The math and (more importantly) the experimentation process have trumped my visualization abilities every time.

So what is the something our universe is expanding into as it becomes the universe, what is the part that is shrinking?

This is a question for a religious or philosophical discussion, as it concerns an unobservable.

[MadMojoMonkey]

This interests me a great deal. I'm not convinced it's 100% true. For example, let's say you're inside a black hole, and it nearly collides with another. Can you know there is another black hole beyond your event horizon? Well, actually, yes, I think so, because each black hole effects the spin of the other.

Again, I can not speculate on what might be inside a black hole, there is simply no data. There is strong reason to believe that no data will ever be available.

The event horizon is a boundary, inside which the gravitational pull is so vast that not even photons can escape. A photon experiences a red shift as it leaves a gravity well. Since it can not trade velocity to pay the energy toll of escaping the gravity well, it pays with it's frequency. The depth of the gravitational well at the event horizon is such that a photon would experience an infinite red shift, giving up ALL of it's energy in the form of added entropy to the system.

Photons, the fastest, least massive particles in the universe can not escape, so what can be "seen" inside it? Something must cross the boundary, in order to be observed, AND it must carry some information from the other side that is not lost in crossing the boundary.

This is how black holes slowly lose their energy, according to my understanding (which may well be very flawed) of Hawkins' ideas. If you can see that your black hole is losing x amount of spin at x rate, you might be able to determine that your black hole is close to another black hole.

Of course, I have no idea if this is true. It's just my interpretation of Hawkins' ideas. But it demonstrates, to me, that the concept we cannot observe beyond an event horizon is perhaps flawed.

Hawking radiation is a strange beast indeed. It is NOT the result of a particle crossing an event horizon from the inside, though. Hawking radiation is a result of space being not empty, but merely the ground state of the sum of all the probabilities of all the possible things that could be there. If enough energy is poured into a finite region of space, particle anti-particle pairs may erupt and annihilate spontaneously (provided all conservation laws are followed, and noting E^2 = p^2c^2 + m^2c^4). They may decay into other particles before they annihilate, and if something strange happens, they may become separated and never annihilate after all.

This final case is what Hawking radiation is. Near the event horizon (like within billionth's of an inch), there is an intense gravitational field. There is an immense amount of gravitational energy. If enough of it sloshes close together, there will be particle anti-particle pairs created. One member of the pair may fall into the event horizon, while the other escapes. In this way, the black hole ejects particles. However, none of the particles that are ejected actually came from inside the event horizon.

[OngBonga]

Yeah man you did good, you didn't fall into my trap, you considered time dilation. tbh I knew you would! I didn't know the answer, I just knew it was less than 2 years. It would take 2 years to an observer in Earth, though it would take an extra year for me to tell them I got there, so 3 years after I leave, they get a message telling them I got there in 1 year 9 months lol. Time is fucking weird, I really don't understand it but it deeply interests me!

Something must cross the boundary, in order to be observed,

Thanks for your reply. This statement alone has released a can of worms in my strange mind. Gonna roll a spliff and take your post in!

[wufwugy]

Incorrect. In theory, it's pretty easy to travel into the future. Going back in time is quite probably impossible, but forwards... it's just a matter of moving very fast.

Let's put our science man to the test, since I absolutely can't argue with his response on the shape of the universe, even though I don't think humans are anywhere near knowing for sure...



If I'm travelling at half the speed of light, how much time does it take me to travel a light year?

Nyet. When the "time travel" question remotely resembles the scifi version i.e non-quantum matter traveling through time outside of the speed of light rule, it is impossible.

If you want to travel forward or back in time the way Doc and Marty did, you need a wormhole. That wormhole requires more energy than is perhaps even possible to generate in the non-birth-stage Universe, and if you do generate it, you tear spacetime and create unbearable and unknown consequences. Even if you can successfully do that, you die as soon as you go through the wormhole. You also need a machine on the other side, which is impossible to build and communicate with

Scifi time travel is a million percent impossible

[MadMojoMonkey]

Is there a question in there?

Also, wormholes are an unobserved phenomenon. They have been predicted by certain solutions of Einstein's Relativistic Field Equations, which predicted black holes as well. So there is some hope that they may one day be found.

However, it is vital to realize that there is no union between Relativistic gravity and Quantum gravity as of yet. There are conflicts with wormholes and quantum gravity, so perhaps quantum gravity has a restriction that is unaccounted for in relativistic gravity. (pure speculation, but then anything about wormholes is pure speculation)

[OngBonga]

wuf, jack asked...

Explain the theoretical basis for time travel.

The theoretical basis is... travel very fast. It might be impossible for us right now, fair enough if that's what you're getting at, but the theoretical basis is there.

It's not theoretically impossible to travel far into the future. It might be to come back, fuck knows about that one.

[OngBonga]

Although another argument, of course, is that if you do indeed travel very fast, you're not travelling into the future, you're just experiencing your now at a different rate to everyone you left behind. When you arrive in the future, it's still your present, it's only the future from point of view of those you left behind.

[a500lbgorilla]

If diamonds are defined as carbons bonded in 3 space with other carbons in such a way that the structure carries stress and strain optimally, does that mean that the surface of a diamond is not diamond?

[MadMojoMonkey]

What? No. Why would it mean that? The surface atoms are still bonded in 3-space. I don't know if they carry stress optimally or not, though.

It's a poor way to define a crystal structure based on its material properties and not it's atomic spacing and bond structure.

[a500lbgorilla]

I just wanted you to describe diamond structure and cleavage planes.

[MadMojoMonkey]

I couldn't do so on either topic without spending a day doing research. Which you could just as easily do yourself. I spent very little time studying crystals and solids, except to shoot x-rays and other radiation at them and measure the angle of displacement of the beam and it's attenuation at various angles.

[givememyleg]

what did you think of the movie primer? i've been obsessing about it and it still mindfucks me trying to figure everything out. and if you haven't seen it, wtfbbq dl that shit now.

[MadMojoMonkey]

Haven't seen it. I just added it to my netflix queue, top slot. I'll get back to you.

[wufwugy]

wuf, jack asked...



The theoretical basis is... travel very fast. It might be impossible for us right now, fair enough if that's what you're getting at, but the theoretical basis is there.

It's not theoretically impossible to travel far into the future. It might be to come back, fuck knows about that one.

Every time I see the "time travel" phrase, it seems to be along the Doc and Marty lines, not the orbit the Earth really fast then come back and find people are old line.

Besides, I'm sure the limit to that sort of travel in time is super duper limited because space is dirty and any machine that gets close to light speed will explode

[MadMojoMonkey]

Besides, I'm sure the limit to that sort of travel in time is super duper limited because space is dirty and any machine that gets close to light speed will explode

What the... ?
Space is dirty?
Velocity is linked to explosion?

Where did you get this? This is not physics.

Do a google search for "Project Orion" if you want to see some real world, practical designs of a city-sized space ship that could easily approach significant speeds for interstellar travel.

[wufwugy]

As to how dirty space is, I don't know; as to how fast something with significant mass can get to the speed of light, I don't know; but at close enough speeds, the spaceship will hit something even small, and the amount of energy generated in the collision will destroy the ship

[MadMojoMonkey]

That would be one very poorly designed ship. It's like saying a car will explode if it drives over 30 mph because it could hit a tree.

[Renton]

Drunk History Nikola Tesla vol. 6 w/ John C. Reilly & Crispin Glover - YouTube

[MadMojoMonkey]

What would happen if a glass of water is suddenly, inexplicably, half-empty?

[chemist]

In your Time Travel answers you forgot to mention that if anyone did actually achieve the necessary speed and break through the light barrier,
they would be turned in to Higgs Bosons.

[MadMojoMonkey]

In your Time Travel answers you forgot to mention that if anyone did actually achieve the necessary speed and break through the light barrier,
they would be turned in to Higgs Bosons.

Um. No.
1) Never did I even slightly insinuate that anything can exceed the speed of light in vacuum.
2) Higgs Bosons do not travel faster than the speed of light in vacuum.

Just to be clear. I didn't mention relativistic mass in any previous discussion, but now it becomes pertinent. As something increases in speed, it also increases in mass by that gamma factor I calculated earlier. The result is that it takes more and more force to accelerate the object. As the speed of light is approached, the mass of the object approaches infinity, so that the following statement is true:

All of the energy in the universe is not enough to accelerate anything to the speed of light in vacuum.

[chemist]

Don't think it works in a vacuum.

[MadMojoMonkey]

The reason for saying "speed of light in vacuum" and not just "speed of light" is because light travels slower as it passes through materials based on the material's index of refraction, a material property. For example, light travels more slowly through glass than through empty space.

[Sasquach991]

If you are travelling at greater than the speed of light and you turn your headlights on, will they work?

[MadMojoMonkey]

I wish I could answer this, but as previously stated, any question which concerns something that has never been observed is fit for a philosophical or religious discussion. Physics can not add anything to those conversations.

Nothing has ever been observed that moves faster than the speed of light. Well, kind of.

If you point the beam of a flashlight at a wall, a slight rotation of the flashlight can cause a large move in the location the beam strikes the wall. The spot on the wall can move faster than the speed of light, if the wall is sufficiently far away. However, the signals (light beam) which produce the spot do not travel faster than the speed of light. Similarly, a shadow can move faster than the speed of light.

There are other examples in which some observed phenomenon appears to violate the cosmic speed limit. However, appropriate applications of the theory of relativity can always demonstrate that none of these phenomena are capable of carrying information faster than the speed of light.

*note the use of the word information in this context means ANY measurable connection between the prior and subsequent states in the apparent violator.

The spot on the wall does not carry the information from the flashlight, the beam carries the information, and the beam does not violate the speed of light.

[Renton]

If two light particles are on a direct colliding course, are they relatively (to each other) moving at 2x the speed of light?

[chemist]

I like the theoretical question about the headlights working,
I would suggest they would because the speed of light is not infinite, so you can have the speed of light +1, and as the headlights are 'in theory' traveling at the speed of light, the light emanating from them would still be relative to the headlight.
I'd also like to know whether light is a particle or a wave.

But anyway a similar but easier question regarding an observable speed.

If you are traveling at the speed of sound and you fart, can anyone hear you,
or smell you, (what speed do smells travel at)?

[chemist]

The reason for saying "speed of light in vacuum" and not just "speed of light" is because light travels slower as it passes through materials based on the material's index of refraction, a material property. For example, light travels more slowly through glass than through empty space.

A farmer is having problems with his chickens. They are all suddenly getting very sick and he doesn't know what is wrong with them.
After trying all conventional means, he calls a biologist, a chemist, and a physicist to see if they can figure out what is wrong.
The biologist looks at the chickens, examines them a bit, and says he has no clue what could be wrong with them.
Then the chemist takes some tests and makes some measurements, but he can't come to any conclusions either.
So the physicist tries. He stands there and looks at the chickens for a long time without touching them or anything. All of the sudden, he starts scribbling away in a notebook.
After several gruesome calculations, he exclaims, "I've got it! But it only works for spherical chickens in a vacuum."

[MadMojoMonkey]

If two light particles are on a direct colliding course, are they relatively (to each other) moving at 2x the speed of light?

This is dipping your toe into the realm beyond physics. I can only answer this in terms of taking a limit of 2 objects approaching each other at a velocity that approaches the speed of light (others may do better).

The relevant outcome is that they only appear to be approaching each other at 2x the speed of light in a stationary reference frame. They do not view each other as moving faster than the speed of light.

Example:
Ongie is approaching me from the left at 99% the speed of light and Renton is approaching me from the right at 99% the speed of light. (The equation is much simplified if they are approaching at the same speed, but this is a minor tweak to make a simplified example.)

In my reference frame, they are approaching each other at 1.98 the speed of light.

In either of their reference frame, I appear to be approaching them at 99% the speed of light, and beyond me they see the other approaching at:

2*beta/(1 + beta^2) = 2*0.99/(1 + 0.99^2) = 1.98/(1 - 0.9801) =

99.994 950 % the speed of light, which is still less than the speed of light.

To talk about photons, I take the limit as beta goes to 1, and the result of the equation is clearly
2*1/(1 + 1^2) = 2/2 = 1.

So 2 photons approaching each other see a photon traveling at the speed of light coming toward them... or do they?

This is where it gets really fun. As anything approaches the speed of light, the gamma factor approaches infinity. This means that they experience infinite space contraction, infinite time dilation, and infinite mass increase.

Good thing photons have no mass, that gets us cleanly out of that universe ending debacle. Whew.

Infinite space contraction: the entire universe appears as an infinitely thin disk, which photons pass through short ways.

Infinite time dilation: none of the clocks in the universe tick, in fact time is completely frozen from the photons' reference frames.

[Renton]

Can you explain, in simple terms, how orbit works and how it is stable?

As I understand it, the earth is in a constant state of falling toward the sun and "sling-shotting" around it, but my question is why is there a lateral force causing it to move transversally to the sun instead of falling perpendicularly straight down?

[MadMojoMonkey]

I like the theoretical question about the headlights working,
I would suggest they would because the speed of light is not infinite, so you can have the speed of light +1, and as the headlights are 'in theory' traveling at the speed of light, the light emanating from them would still be relative to the headlight.

If you are traveling under the speed of light (by even the slightest infinitesimal amount, then there is a clear answer. The speed of light in vacuum is constant in all inertial reference frames. Therefore, your headlights look normal to you.

I'd also like to know whether light is a particle or a wave.

Yes. There is no physical distinction between a particle and a wave in quantum mechanics.

In fact a man named J. J. Thompson won the Nobel prize in physics in 1906 for his work demonstrating that electrons are particles. Then in 1937, his son, G. P. Thompson received the Nobel prize in physics for his work demonstrating that electrons are waves.

I, personally, have recreated experiments that demonstrate both the wavelike and particle-like behavior of photons. I speak with firsthand knowledge that photons are BOTH waves AND particles.

But anyway a similar but easier question regarding an observable speed.

If you are traveling at the speed of sound and you fart, can anyone hear you,
or smell you, (what speed do smells travel at)?

Yes, anyone who is behind the shock wave will hear you (assuming your flatulence was released with a proud rapport that made you question the changing of your under-linens.)
Even those in front of the shock wave may hear evidence of your foul emanation after the wave front has passed them.

The speed of smell is a function of fluid dynamical factors such as ambient flow, turbulence, temperature, nearby surfaces, viscosity of the carrier fluid, etc.

[MadMojoMonkey]

As I understand it, the earth is in a constant state of falling toward the sun and "sling-shotting" around it, but my question is why is there a lateral force causing it to move transversally to the sun instead of falling perpendicularly straight down?

According to this view of gravitation (Newton's), it is the inertial force, or momentum of the Earth tending to move in a straight line, and leave orbit.

Can you explain, in simple terms, how orbit works and how it is stable?

There are at least 4 simple answers to this question. All of them are correct, but they hinge of very different fundamental principles.

Newtonian Mechanics: Massive bodies exert a force on each other that is proportional to the product of their masses and the inverse square of their distances.
F = G*Mm/r^2 ; where M and m are the masses of the bodies and r is the distance between them. G is Newton's gravitational constant; it is the ratio of proportionality. Additionally, the force is always attractive.
Good: We sent people to the moon with Newtonian theories of gravity. Also theorized the outer planets and later discovered them. This is the hallmark of good science. Is local in time
Bad: How does a planet calculate it's distance from the sun? Is non-local in space.

Local Potential: There is a gravitational field which exists everywhere in space. The force on any body is determined by the gravitational field in the immediate vicinity.
The motion of bodies is explained by taking the body's inertia into account and then observing the gravitational potential in the immediate vicinity. This is the equivalent of saying you don't need the entire topographical map of the Earth to know where a river will flow, you only need to know the velocity of the flow and the slope at the boundaries (banks) of the river.
Good: is local in space
Bad: is non-local in time

Path of least action: A body follows the path from A to B that minimizes the total energy required to get from A to B in some given time.
Good: is local in space and time
Bad: assumes a body can postulate multiple paths and pick the best one.

Relativity: All bodies follow straight paths through curved space-time. Gravitational forces are illusory. Bodies do not travel in curves, and are therefore not being accelerated laterally. The curvature of space-time is a function of all bodies in the universe, but "gravitational information" is limited to travel at the speed of light.
Good: Is amazingly accurate at describing "exotic" phenomena that Newton's Theory of Gravitation left unexplained. Has made many predictions, like black holes, which have later been verified.
Bad: Is needlessly complex for situations where space-time is "basically flat".

EDIT: I will get into how each of these theories explains a closed, stable orbit in a later edit. I had to dig up some old stuff to answer this much. Honestly, there is a whole course on orbital mechanics that I did NOT take, so I'm just a rookie at this type of stuff.

[Renton]

Thanks a lot for explaining this, I find it extremely interesting.

So according to Newton, in order for Earth to orbit the Sun, it must have been in a state of accelerating in a direction not toward the Sun, i.e. Newton's cannonball. But relativity explains this better?

[MadMojoMonkey]

I am going to speak of orbits in terms of the 2 body problem. The fundamental assumption is that the 2 bodies in question have masses that are "far greater" than any other masses "nearby". This is a simplifying assumption for the sake of example.

There are 3 possible interactions that can take place in the 2 body problem.
1) The bodies will orbit each other in elliptical paths.
2) The bodies will move past each other in parabola shaped paths.
3) The bodies will move past each other in hyperbola shaped paths.

Newtonian mechanics: There is a critical speed which determines which path is taken. This is the escape velocity (it should be named escape speed, since direction is irrelevant). If the bodies' relative speed (the speed of one body in the other body's reference frame) is less than their escape velocity, they will have closed, stable orbits about each other. If they are moving at escape velocity they will swing past each other once in a parabola. If they are moving above escape velocity, they will swing past each other once in a hyperbola.

Local potential: I don't know. I'm sure there is an answer, but I don't have it.

Path of least action: For a closed, stable orbit, there is some path from A to A over some period of time for which the change in energy is zero. This path is the orbit.

General Relativity: Space-time is curved by the presence of mass. The curvature of space-time contains certain paths, called geodesics, which are closed loops. Imagine contour lines on a topographical map, except in 3-D space. If a body is moving along one of these lines, it will continue to move along the line without deviation unless acted on by some outside force. (Echos of Newton's First).

Thanks a lot for explaining this, I find it extremely interesting.

The pleasure is all mine. With all I'm learning from reading and re-reading your many informative posts, it is nice to be able to give something back. The thanks are heartily returned.

So according to Newton, in order for Earth to orbit the Sun, it must have been in a state of accelerating in a direction not toward the Sun, i.e. Newton's cannonball. But relativity explains this better?

Short answer: not accelerating, moving is enough. The Earth had some momentum which was not toward the sun, which, in the lack of friction or some other dissipating force, is still present.

Relativity explains it differently, but "better" is subjective. From a strictly physics viewpoint, General Relativity is the most accurate model. From a "put an SUV on Mars" viewpoint, Newtonian mechanics is accurate enough without being needlessly complex. Except for the orbit of Mercury, Newtonian mechanics is adequate to describe the solar system.

Long answer:
The rotations in the solar system have been present from its earliest formation. When the sun's prior incarnation (our sun has gone supernova at least once before) was first formed in the collapse of a stellar nebula, there was rotation. The atoms in the nebula were not falling straight toward the gravitational center. The nebula collapsed in a swirling spiral, and created a spinning star. This star had no planets, as the nebula which formed it contained mostly Hydrogen and some Helium.

Eventually, this star exploded in a supernova and spewed its atoms back out into a new stellar nebula. This new nebula had exactly the same total rotation as the star that created it, which had exactly the same total rotation as the nebula from which it formed. However, now the atoms are different. There is an abundance of "heavy metals" that were created in the supernova, not to mention the Carbon, Nitrogen, and Oxygen that were created in vast quantities by "normal" fusion before the supernova.

Another collapse, another spinning star, we'll call this star the sun. Now, there are heavy elements causing local areas of high density, which act as minor gravitational centers. The collapse is less uniform, and planets, moons, comets, etc. are formed. Still, the total rotation in the system hasn't changed for billions of years, this is called the law of conservation of angular momentum.

Due to the law of conservation of angular momentum (one of the strongest conservation laws known), the solar system today still bears that rotation. Some of it is in the rotating of the sun, planets and moons. Some of that rotation is in the orbits of these bodies.

[a500lbgorilla]

An orbit is moving forward fast enough that you miss as you fall toward the Earth. If you're orbiting the earth at an altitude you would consider in space, you're in free fall like a skydiver; but you've got so much forward velocity and no air to hold you back that the Earth moves out of the way below you.

You fall to the Earth and perpetually miss. You just move forward so fast, the Earth seemingly moves out of the way.

[a500lbgorilla]

Also, the Sun didn't catch the Earth. The Earth and Sun formed together. A whole cloud of stuff started rotating a long time ago and it evolved under a set of known-ish laws to form what you see today. One of those laws is the conservation of rotational momentum. Your rotational momentum is your velocity, by your mass, by how far you are from the center of mass in 3-space. The total rotational momentum of the cloud of stray stuff way back which formed our solar system is equal to the total rotation momentum of the solar system today. That includes all comets, asteroids, planets, etc which originated with us, even if some of it had been flung off. This includes all the momentum being used to move those Voyager spacecraft out of our solar system.

So the Earth and Sun accreted from the same cloud of stuff already spinning, one seemingly around the other, each around their combined center of mass.

[CoccoBill]

An orbit is moving forward fast enough that you miss as you fall toward the Earth. If you're orbiting the earth at an altitude you would consider in space, you're in free fall like a skydiver; but you've got so much forward velocity and no air to hold you back that the Earth moves out of the way below you.

You fall to the Earth and perpetually miss. You just move forward so fast, the Earth seemingly moves out of the way.

That's all quite intuitive. What isn't however, is that wouldn't even a slight change in velocity, even the tiniest bit of acceleration or deceleration cause the planet to either get loose or crash? How come this doesn't happen? What creates this universal (ha!) tendency for all objects to just play nice and circle each other at exactly the right speed?

Well, it's a logical fallacy. The ones with the incorrect speed have indeed already left the orbits or will do so later. None of the orbits are stable, for example the moon is moving away from earth at 3.8cm/year, and will eventually break loose. More about it here: Curious About Astronomy: Is the Moon moving away from the Earth? When was this discovered?. Ok, some orbitses(? orbii? wtf) are quite stable, such as earth's orbit around the sun. There are tiny oscillations in the elliptical orbit, but none of them suggest we're moving neither towards nor away from the sun. There are, however, a couple other forces at play. One is the same tidal interaction as between the earth and the moon, just quite a bit weaker. It turns out that the yearly increase in the distance between the earth and the sun from this effect is about one micrometer (a millionth of a meter, or a ten thousandth of a centimeter). Another effect is that due to the sun being powered by nuclear fusion, it's continuously losing mass, causing earth's orbit to widen. However, over the lifetime of the sun, about 10 billion years, it will only lose about 0.1% of its mass, causing the earth to move out by a total of about 150,000km, that is, about 1.5cm/year. So, we're not breaking loose anytime soon.

[MadMojoMonkey]

You fall to the Earth and perpetually miss.

This whole post is a valid view of orbits. It falls into the realm of the "orbits are the result of forces" descriptions. This is NOT the only theory, or even the most accurate. It is adequate, but putting it out there like it is the stone cold nuts of explanations might be misleading for some.

If we were describing the orbit of Mercury, we would need General Relativity. So GR is, strictly speaking, the most "correct" model. It predicts and explains gravitational lensing, black holes, and other observed phenomena, which the other theories do not.

Also, the Sun didn't catch the Earth.

This is another good point. I didn't mean to imply anything other than what is stated here.

The sun probably did catch Mercury, but likely it was a body that got flung toward the sun from the outer solar system, then interacted with something else when it was near its current orbit, which it then settled into.

[MadMojoMonkey]

... wouldn't even a slight change in velocity, even the tiniest bit of acceleration or deceleration cause the planet to either get loose or crash?

Most accelerations would only result in a different shape of orbit (a change in the eccentricity of the ellipse), and a different orbital period. Only when 2 bodies are moving near their escape velocity and some interaction accelerates them to or above the escape velocity would they break orbit. Anything which reduces the relative speed would result in another "stable" orbit, or a collision.

Well, it's a logical fallacy. The ones with the incorrect speed have indeed already left the orbits or will do so later.

There is a lot of random motion is the early formation of a stellar system, and the localizing of the masses causes more and more instability in the surrounding areas. Planets "clear" their orbits, either by accretion, or by "swinging" smaller bodies away from the orbit. Most of these swings leave the smaller body moving out of the solar system.

None of the orbits are stable

The notion of stability is clear in the 2 body problem, but that's not the whole picture. There are thousands of bodies in the solar system. That's not really the issue here, as you've stated. The real issue is that we've been talking about stability without giving a time frame.

"In the long term Pluto's orbit is in fact chaotic. While computer simulations can be used to predict its position for several million years (both forward and backward in time), after intervals longer than 10–20 million years, calculations become speculative: Pluto's tiny size makes it sensitive to small details of the Solar System, hard-to-predict factors that will gradually disrupt its orbit." ... "This does not mean Pluto's orbit itself is unstable, but its position on that orbit is impossible to determine so far ahead."
- Wikipedia "Pluto"

Your info about the orbits of the moon and Earth are solid, to my knowledge.

Another effect is that due to the sun being powered by nuclear fusion, it's continuously losing mass.

The mass loss is not strictly due to fusion, merely that its temperature is above absolute zero is enough. Anything with a non-zero temperature is radiating heat (by way of releasing photons through blackbody radiation). Heat is a measure of energy. The object releases energy, therefore the object loses mass, QED.

The mass loss rate of the sun, based on E = mc^2 (m = E/c^2), and dividing both sides of the equation by time is:

Solar photon energy output at Earth: 1,368 W/m^2
Earth's mean orbital distance: 149.6 x 10^9 m
Surface area of a sphere with that radius: 4*pi*r^2 = 2.812 x 10^23 m^2
Total photon power output of the sun: 1,368 W/m^2 x 2.812 x 10^23 m^2 = 3.847 x 10^26 W
Speed of light: 2.998 x 10^8 m/s
Speed of light, squared: 8.988 x 10^16 m^2/s^2
Solar mass loss rate: 3.847 x 10^26 W / 8.988 x 10^16 m^2/s^2 = 4.281 x 10^9 [units]
W = J/s = kg m^2 / s^3 ; [units] = kg/s

Solar mass loss rate: 4.281 x 10^9 kg/s

That's over 4 billion kilograms per second in light alone! Oh yeah, the sun's mass is roughly 2 x 10^30 kg, so dropping 10^9 kg/s is nothing at all.

The fusion processes release veritable torrents of neutrinos, which also contribute to the mass loss rate. Neutrinos are incredibly abundant, but are nearly mass-less and interact so weakly that they are difficult to detect. In fact, billions of neutrinos have sped through your body at nearly the speed of light during the time it took you to read this sentence. If it's night time, those neutrinos passed through the planet before they passed through you. How cool is that!?!

Even still, as you've stated, the total mass loss rate is negligible when compared to the sun's mass. More relevant is the natural evolution of a star like our sun. While remaining constant in temperature, the sun's size and luminosity increase over time. In about 1 billion years, this increase will be enough to boil the earth's oceans.

... but what if global warming is a fraud, and we make the world a better place for nothing?