How Can Rockets Travel To The Moon, If MoonTravels at 6mKPM

[Zelio]

Currently, the "fastest" object created is Voyager 1, it runs at 61333 km/h (speed relative to sun) and it leaved solar system...

[Sjc1000]

Aahh this just reminds me of the question.

If you are ( somehow. If someone figures out how PLEASE TELL ME ) traveling in a car at the speed of light, and you turn on the headlights. What would happen?

A) They beam out in front, like normal. Regardless of your speed.
B) The light goes nowhere because it cannot move faster than you are.

[tomoe_uehara]

I think it will be like walking along with your dog, it will stay beside you if your speed is the same.
But since you're on a car, then the light stays inside of your headlights.

[xZomBie]

Do you have the correct answer? I choose B.

[jethrow]

From what perspective - you in the car, or someone standing still outside the car? If you look look at yourself in the mirror, you will still see your reflection, and you will still see your headlights as normal. But then, how do we measure what we see - what medium is it relative to?

[Zelio]

I extrapolate if the traveler is a human with eye, I think you will have a frozen image if you look at your back but not in other directions, it will be like a distortion (warp) because it is relative, you will catch photon reflected at different time, it will be like old thing and new thing in the same image and that will depends of what direction you look at (eyes angle, relative to your move)... to imagine that light are just flux, and you catch them during your travel.

At your back, it will be always the same image that you saw at the moment just before you reach the speed of light, it will be always the same photons that they are now stuck in your eye and stimulus your photoreceptor cell (rod cell and cone cell). But I dunno maybe they are a quantum mecanism or state on/off needed for your human camera (eye), also there is the problem of the retina persistance because the cell will regenerate with still a photon inside, and how information eye to brain can travel more faster than light.

Edit: http://www.youtube.com/watch?v=JQnHTKZBTI4

[kon]

http://www.theguardian.com/science/2014 ... d-of-light

http://www.physicsforums.com/showthread.php?t=369481

[Sjc1000]

From what perspective - you in the car, or someone standing still outside the car? If you look look at yourself in the mirror, you will still see your reflection, and you will still see your headlights as normal. But then, how do we measure what we see - what medium is it relative to?

The perspective is whoever can see the headlights. But if you really want one, from the car.

Do you have the correct answer? I choose B.

I chose B since light physically cannot move master than the speed of light ( that we know of ).
And if you're travelling at that speed, the lights cannot move faster than you.

[Zelio]

Oh if we need to select an anwser then I say "A" (just to be different of others...)
So, They beam out in front, like normal. Regardless of your speed ? If it is relative, time and space will have distortion, it will depends of the observator, external spectator will not see same thing than the car driver (not 2*C)...

[xZomBie]

I chose B since light physically cannot move master than the speed of light ( that we know of ).
And if you're travelling at that speed, the lights cannot move faster than you.

[trismarck]

Hello,

I don't understand one of the drawings. It looks like there is a distortion of time-space caused by some unidentified object (perhaps an alien ship) which (the object) prevents the rocket from following its projected trajectory.

but I'm not sure if I interpret this correctly. I'll be thankful for any input.

[LinearSpoon]

It's supposed to be a smooth curve. It was a quick drawing done with paint and isn't meant to be a perfect representation of what's going on.

[trismarck]

LinearSpoon, are you sure? I've zoomed the picture and I think I can see a spaceship there:

From the shape of the hull, it's probably a Marklarian one.

[LinearSpoon]

@trismarck, I'm afraid I don't understand your reference, but I do realize there is a joke there.

@Sjc1000, regarding the car & headlights question: If you believe Einstein's theory of special relativity, the answer is A. There's no reason you shouldn't believe the theory, it has been experimentally verified multiple times and even has practical uses, for example in GPS calculations.

The velocity vector addition that we typically use is a simplification of the true formula which works because we tend to deal with speeds that are a small fraction of the speed of light.

Here is Einstein's formula for adding relative velocities a and b to find their total velocity, v relative to the observer. c is the speed of light, which is constant for all observers.

You can see that if a and b are small numbers, the denominator of this formula may as well be 1+0.

Lets analyze this situation. Let a be the velocity of the car, and b the velocity of the light from the headlights. We will choose the driver of the car as the observer.
Relative to the driver, the car is moving 0 m/s. Relative to the driver, the light will exit the headlights at c m/s.
So:

Code: Select all

a = 0
b = c

           0 + c
v =  -----------------
      1 + (0*c / c^2)

       c
v = ------- = c
     1 + 0

The driver will observe the light travelling forward from his car at c, or 299792458 m/s, a number which is exact because the meter is defined based on the speed of light.

As an interesting side point, you can also perform the same calculation as a stationary observer.
The car is moving at c m/s relative to the stationary observer, and the light comes out of the car headlight at c m/s.

Code: Select all

a = c
b = c

           c + c
v =  -----------------
      1 + (c*c / c^2)

      2*c
v = ------- = c
     1 + 1

So the stationary observer also sees the headlight moving at 299792458 m/s relative to himself.

The reason this works out to the same speed is because time passes differently for each observer, and space "shrinks" when observing objects that have a different velocity than your own. This is where people are getting that it is possible to time travel by moving near the speed of light. It should also be noted that this is purely theoretical, it's impossible for any object with mass to reach the speed of light. This is because as you reach higher velocities, your mass will increase, which will end up requiring an infinite amount of force to continue accelerating towards the speed of light.

Some relevant Wikipedia links:
http://en.wikipedia.org/wiki/Velocity-addition_formula
http://en.wikipedia.org/wiki/Length_contraction
http://en.wikipedia.org/wiki/Time_dilation
http://en.wikipedia.org/wiki/Hafele%E2% ... experiment

And a simple calculator. a and b are velocities relative to an observer, Classic Physics returns the common velocity addition, Special Theory returns Einstein's velocity addition. All units are m/s.

Code: Select all

Gui, Add, Text, x12 y9 w100 h30 , a (m/s)
Gui, Add, Text, x12 y39 w100 h30 , b (m/s)
Gui, Add, Text, x12 y69 w100 h30 , Classic Physics`n  a+b
Gui, Add, Text, x12 y99 w100 h30 , Special Theory`n  (a+b)/(1+(ab/c^2))
Gui, Add, Edit, x122 y9 w150 h20 va gUpdate, 0
Gui, Add, Edit, x122 y39 w150 h20 vb gUpdate, 0
Gui, Add, Edit, x122 y69 w150 h20 ReadOnly vClassic
Gui, Add, Edit, x122 y99 w150 h20 ReadOnly vSpecial
Gui, Show

c := 299792458  ;speed of light in m/s

Update:
  Gui, Submit, NoHide
  GuiControl,, Classic, % a+b
  GuiControl,, Special, % (a+b)/(1+(a*b/c**2))
return

GuiClose:
  ExitApp
return

Some interesting things to try:
1. Very low values for a and b.

Spoiler

Notice that both calculations are approximately the same (or even exactly the same, due to the imprecise nature of floating point numbers in computers). This is why we used the original calculation, because humans rarely if ever measured or dealt with high enough speeds for the difference to matter. This is also why the simpler formula is still widely used and taught in schools, because the difference won't matter for the average person.

2. Values of 500,000 for each.

Spoiler

Here you should start to see the results for Classic vs Special drift apart. Even still, the difference is so small it could easily be mistaken for a measurement error...This is why we didn't really notice a problem until the late 1800s when Maxwell's equations were found to conflict with classical motion mechanics.

3. The speed of light (299792458) for a and any other value for b.

Spoiler

This is where people are getting that the speed of light is the "speed limit" of the universe...This is also where the Classic formula is most lacking - in prediction of very high speed objects.

I hope that explanation wasn't too detailed. I think I got carried away researching it..fascinating stuff though.

[trismarck]

LinearSpoon, you seem to be mad at me that I doodled on your drawing.

Initially I've thought that those doodles would just be funny, but I can see they could also be interpreted as offensive depending on how serious one treats the topic. It wasn't my intention to look at it this way.

[Morpheus]

FWIW I thought it was funny.

[smorgasbord]

Code: Select all

Gui, Add, Text, x12 y9 w100 h30 , a (m/s)
Gui, Add, Text, x12 y39 w100 h30 , b (m/s)
Gui, Add, Text, x12 y69 w100 h30 , Classic Physics`n  a+b
Gui, Add, Text, x12 y99 w100 h30 , Special Theory`n  (a+b)/(1+(ab/c^2))
Gui, Add, Edit, x122 y9 w150 h20 va gUpdate, 0
Gui, Add, Edit, x122 y39 w150 h20 vb gUpdate, 0
Gui, Add, Edit, x122 y69 w150 h20 ReadOnly vClassic
Gui, Add, Edit, x122 y99 w150 h20 ReadOnly vSpecial
Gui, Show

c := 299792458  ;speed of light in m/s

Update:
  Gui, Submit, NoHide
  GuiControl,, Classic, % a+b
  GuiControl,, Special, % (a+b)/(1+(a*b/c**2))
return

GuiClose:
  ExitApp
return
 

Thanks for this example @LinearSpoon