o rly? [updated! Ack, need help in Quantum Physics]

[andylawcc]

Updated:
I have to do an simple analysis on Heisenberg's Uncertainty Principal. Basically, the professor wants us to understand the principal, not just memorizing the "Big words," technical terms, and equation; he just know to know if we really understand it or not in layman terms.

So, my conception is:

Not to be confused with the Observer Effect, Heisenberg's Uncertainty Principle is a mathematical equation that determines the uncertainty in measurement. Even with an infinitely precise instrument, Heisenberg argued that there is still a margin of error due to.... [i don't know how to go on from this point]


So far, does my intrepretation sound right?





Original Post:
i am taking an Astronomy class, here's some of the questions:

1) Suppose you drive your car at 50 mph, and I drive mine, in the same direction, at 60 mph. Relative to you I move with the speed of ...

answer: 10mph

easy, next.


2) Suppose you drive your jet plane away from me at half the speed of sound and I am playing on the ground by making some loud explosions. The sound of my explosions catches up with you with the speed equal to ...

answer: half the speed of sound

okay, not that hard neither, next


3) Suppose you drive your spaceship away from me at half the speed of light and I am playing on the ground by making some lightning. The flash of my lightning catches up with you with the speed equal to ...

answer: speed of light


and I thought it would be "half speed of light" as I used and apply the logic from the first 2 questions.

 

[Leros]

The 3rd one merely asks what the speed of the light is, not the relative speed to the spaceship.

 

[Cabages]

Im taking a complete shot in the dark, and I only know a little from a physics class in high school.

But I would say that the speed of light is the speed of light. It cant really be slowed down, but diverted. The reason the sound is slower is because it is a wave, and has to resonate through objects?

Again, complete shot in the dark, but I am interested in the answer.

 

[SVT Cobra]

The answer is in the two postulates of the theory of relativity:

In simple terms, everyone measures the speed of light to be the speed of light in any reference frame.

 

[2Xtreme21]

The speed of light is c in any and every reference frame. Learn that and accept that now or you're gonna have one hell of a time understanding the rest of the material that follows relativity in your physics cirriculum.

Edit: Responding to the sound is a wave but light isn't comment earlier:

Light is electromagnetic radiation. All EM radiation travels at a constant speed of 3.0x10^8 m/s.

OP the reason I say to accept this now is because likely the next thing you're going to cover is the Lorentz factor, which deals with contraction of length and time dilation. Essentially, the faster you go, the "slower" time moves (relative to everyone else), and the shorter lengths become (relative to you). This is a damn hard concept to understand and will go against the newtonian physics you've been taught ever since the beginning of your physics class. Thing is it's incredibly interesting and you'll get a new view of the world if you can make it through.

 

[andylawcc]

Originally posted by: 2Xtreme21
The speed of light is c in any and every reference frame. Learn that and accept that now or you're gonna have one hell of a time understanding the rest of the material that follows relativity in your physics cirriculum.

oh, it's just an intro Astro class. no quantum physics will follow after this

edit:

to 2Xtreme21:

again, this is just an intro class. that Lorentz dude/thing was mentioned somewhere later but only has one or two question in the midterm about it.

time dilation is a truely interesting concept: I am surprised ATOT hasn't talked about it before.

 

[2Xtreme21]

Hah in that case, pfft.

Yeah I took a class called Space, Time, Light, and Matter. It was damn hard but man I left that class with a new view of the world... it's just amazing how different things are in the reeeeeal big and the reeeeeal small.

 

[Jeff7]

If you're in something which moves, time slows down for you. Speed is a function of time, so if distance travelled per second changes, then the speed changes. However, if the rate at which time passes changes, this also affects speed.

Sound is so slow that the effects of relativity on objects at that speed is negligible.
Half the speed of light? Now that's more significant.

So, you're in the spaceship travelling at half the speed of light. To a bystander, a beam of light leaving your spaceship is travelling at the speed of light, c. To you, it also appears to be moving at the same speed, relative to you.
The thing to note though is, since your speed is so great, your perceptions are also slowed down. Let's say that light moves at 10 meters per second.
To the passerby, the light beam moved 10 meters in 1 second. But your perception of what "1 second" represents has been slowed down. The light still moves 10 meters relative to you, but since time for you is slowed down, the light has longer to travel that 10 meters.

Result: you see the light move away from you by 10 meters in one second, because your second is slower than a second for the stationary bystander.


At least, that's my understanding of it.

 

[andylawcc]

Originally posted by: Jeff7
If you're in something which moves, time slows down for you. Speed is a function of time, so if distance travelled per second changes, then the speed changes. However, if the rate at which time passes changes, this also affects speed.

Sound is so slow that the effects of relativity on objects at that speed is negligible.
Half the speed of light? Now that's more significant.

So, you're in the spaceship travelling at half the speed of light. To a bystander, a beam of light leaving your spaceship is travelling at the speed of light, c. To you, it also appears to be moving at the same speed, relative to you.
The thing to note though is, since your speed is so great, your perceptions are also slowed down. Let's say that light moves at 10 meters per second.
To the passerby, the light beam moved 10 meters in 1 second. But your perception of what "1 second" represents has been slowed down. The light still moves 10 meters relative to you, but since time for you is slowed down, the light has longer to travel that 10 meters.

Result: you see the light move away from you by 10 meters in one second, because your second is slower than a second for the stationary bystander.


At least, that's my understanding of it.

head explodes upon reading the 16th word

 

[NikolaeVarius]

Originally posted by: Jeff7
If you're in something which moves, time slows down for you. Speed is a function of time, so if distance travelled per second changes, then the speed changes. However, if the rate at which time passes changes, this also affects speed.

Sound is so slow that the effects of relativity on objects at that speed is negligible.
Half the speed of light? Now that's more significant.

So, you're in the spaceship travelling at half the speed of light. To a bystander, a beam of light leaving your spaceship is travelling at the speed of light, c. To you, it also appears to be moving at the same speed, relative to you.
The thing to note though is, since your speed is so great, your perceptions are also slowed down. Let's say that light moves at 10 meters per second.
To the passerby, the light beam moved 10 meters in 1 second. But your perception of what "1 second" represents has been slowed down. The light still moves 10 meters relative to you, but since time for you is slowed down, the light has longer to travel that 10 meters.

Result: you see the light move away from you by 10 meters in one second, because your second is slower than a second for the stationary bystander.


At least, that's my understanding of it.

Hit it right on the money

 

[Jeff7]

Originally posted by: andylawcc
head explodes upon reading the 16th word

Aw come on, that's simplified.


When you move really fast, what you call a second changes. You get slow in the head.
So a normal person standing still says that a second is really quick, and so light can't get very far in that time.

But you in the spaceship are now Mr. Deadhead, thinking so slow you wouldn't have time to interpret a Knock-knock joke. You watch that same beam of light moving from your ship. Several real-world-seconds may pass for you, but since you're now slow in the head, you think only one second passes. That gives that light plenty of time to get 10m away from your ship.

 

[2Xtreme21]

It's not an easy concept to explain. Because V = dx / dt, and your speed remains constant, one of the two (dx - length or dt - time) must change. If you're in a space ship travelling .5c and you're approaching an object that is 100m long, let's say, the length at which it's going to appear to you is significantly shorter:

? = 1.155 given from the fact that your ship is moving .5c (there's an equation that will get you this number). Your contracted length is given by L' = L0 / ? = 100m / 1.155 = 86.6m is how long the object would appear to you as.

Similarly if someone was orbiting the earth at the speed of .5c, the ticks of the second hand on his watch (if you could see them) would appear longer than the ticks on a normal watch "at rest." Example:

dt = ? * dt0 where dt0 is the normal, at rest time of a ticking second hand (i.e. 1 second). In this case, the ticks on his watch, according to YOU the observer, would take dt = 1.155 * 1 = 1.155 seconds.

As you can see it's not incredibly different, but fast speeds screw with time and length.

That being said, there is a lorentz factor for ANY speed above rest. Those on airplanes that travel at 500MPH theoretically have a longer second (again, as observed from someone at rest) than the person at rest himself. Granted, the difference is so miniscule (671,081 MPH is .1c and the time dilation (dt) for 1 second is 1.005 seconds), but it exists. Something to think about.

 

[BrownTown]

Originally posted by: 2Xtreme21
Light is electromagnetic radiation. All EM radiation travels at a constant speed of 3.0x10^8 m/s.

Nah, thats only the speed of light in free space, in reality C = 1/sqrt(e0*u0)

 

[andylawcc]

Originally posted by: Jeff7

Originally posted by: andylawcc
head explodes upon reading the 16th word

Aw come on, that's simplified.


When you move really fast, what you call a second changes. You get slow in the head.
So a normal person standing still says that a second is really quick, and so light can't get very far in that time.

But you in the spaceship are now Mr. Deadhead, thinking so slow you wouldn't have time to interpret a Knock-knock joke. You watch that same beam of light moving from your ship. Several real-world-seconds may pass for you, but since you're now slow in the head, you think only one second passes. That gives that light plenty of time to get 10m away from your ship.

okay, much better

 

[SVT Cobra]

For those that do not grasp the concept of time dialation just imagine a clock which measures the time it takes for light to bounce off of two horizontal mirrors. For the person standing still the light moves between the mirrors as you would imagine. At speeds close to the speed of light however, that light beam is not just moving up and down, it is traveling now sideways, giving a slanted path from t0 to tf. This exists everywhere at any speed, except at speeds that are not close to the speed of light, the difference in the time it takes for the beam to bounce back and forth is extrememely negligble.

 

[Cabages]

Originally posted by: 2Xtreme21
Hah in that case, pfft.

Yeah I took a class called Space, Time, Light, and Matter. It was damn hard but man I left that class with a new view of the world... it's just amazing how different things are in the reeeeeal big and the reeeeeal small.

Cool, ive always been interested in light and these kinds of things. So you would reccomend a class like that? And that was in college right?

 

[andylawcc]

updated!!!


Updated:
I have to do an simple analysis on Heisenberg's Uncertainty Principal. Basically, the professor wants us to understand the principal, not just memorizing the "Big words," technical terms, and equation; he just know to know if we really understand it or not in layman terms.

So, my conception is:

Not to be confused with the Observer Effect, Heisenberg's Uncertainty Principle is a mathematical equation that determines the uncertainty in measurement. Even with an infinitely precise instrument, Heisenberg argued that there is still a margin of error due to.... [i don't know how to go on from this point]


So far, does my intrepretation sound right?

 

[kedlav]

that'd probably work just fine as a summation for an intro course, yes

 

[andylawcc]

Originally posted by: kedlav
that'd probably work just fine as a summation for an intro course, yes

okay thanks. it is for an intro course so it doesn't require a lot of precision (no pun intended)


anyways, how do I end the last sentence though?
Even with an infinitely precise instrument, Heisenberg argued that there is still a margin of error due to....

should I just leave out the last 2 words?

 

[andylawcc]

okay Jeff7 it doesn't have to be that long ;P

 

[everman]

I killed Schroedinger's cat.

 

[Jeff7]

The reason behind the Uncertainty principle:

Let's say you want to observe an electron. Assume it is contained in a perfect vacuum, a container devoid of everything. Now if you wish to observe it, you need to hit it with energy to detect it. Problem: as soon as energy hits that electron, it will move.
So, you're left with a choice.
You can find out its position very precisely by hitting it with a bunch of photons from all over the place, but in doing so, you change its velocity to some unknown value. Sure you can use math to figure out what it might be, but that value isn't certain.

If you want to nail down its velocity, doing so will change the electron's position to some unknown value.

You can only have one or the other, but not both at the same time, as measuring one property changes the other.


Do you watch Futurama? There was an episode with a really close horse race.
Announcer: "And the winner is, 'Something-or-other in a quantum finish!'"
Professor Farnsworth: "No fair! You changed the outcome by measuring it!"



That brings up something else that is semi-relevant: a perpetual motion machine. Such a device could never be observed. Doing so would require that some matter or energy beam be reflected off of the device to allow observers a glimpse of the miraculous machine. But that would mean that it is no longer self-perpetuating, as it would then have an outside source of energy. Oops, you just effectively destroyed the perpetual motion machine by observing it!

Originally posted by: andylawcc
okay Jeff7 it doesn't have to be that long ;P

That's what she sa!!!!......aw nevermind.

 

[andylawcc]

Originally posted by: Jeff7
The reason behind the Uncertainty principle:

Let's say you want to observe an electron. Assume it is contained in a perfect vacuum, a container devoid of everything. Now if you wish to observe it, you need to hit it with energy to detect it. Problem: as soon as energy hits that electron, it will move.
So, you're left with a choice.
You can find out its position very precisely by hitting it with a bunch of photons from all over the place, but in doing so, you change its velocity to some unknown value. Sure you can use math to figure out what it might be, but that value isn't certain.

If you want to nail down its velocity, doing so will change the electron's position to some unknown value.

You can only have one or the other, but not both at the same time, as measuring one property changes the other.


Do you watch Futurama? There was an episode with a really close horse race.
Announcer: "And the winner is, 'Something-or-other in a quantum finish!'"
Professor Farnsworth: "No fair! You changed the outcome by measuring it!"



That brings up something else that is semi-relevant: a perpetual motion machine. Such a device could never be observed. Doing so would require that some matter or energy beam be reflected off of the device to allow observers a glimpse of the miraculous machine. But that would mean that it is no longer self-perpetuating, as it would then have an outside source of energy. Oops, you just effectively destroyed the perpetual motion machine by observing it!

head explodes for the second time.


hehe, no, this time i got it. But isn't what you stated in the first half the Observer Effect instead? Or, does Observer Effect = Uncertainty Principle.

what about this equation?
http://upload.wikimedia.org/math/a/8/a/a8a3469365ba9e28b216ecb0de43dff0.png

 

[Jeff7]

Originally posted by: andylawcc
hehe, no, this time i got it. But isn't what you stated in the first half the Observer Effect instead? Or, does Observer Effect = Uncertainty Principle.

what about this equation?
http://upload.wikimedia.org/math/a/8/a/a8a3469365ba9e28b216ecb0de43dff0.png

My turn for head explosion.
I never learned the math. I just know the conecpts.

To my knowledge, what I described is what the Uncertainty Principle is talking about.

 

[andylawcc]

what about this equation?
http://upload.wikimedia.org/math/a/8/a/a8a3469365ba9e28b216ecb0de43dff0.png

My turn for head explosion.
[/quote]


http://www.videosift.com/video/Monty-Python-Holy-Grail-The-Bridge-of-Death