The Rocket Ship

[Motor Daddy]

It is not contingent on distance, but on relative velocities.

 

Velocity is what, d/t? What does another object have to do with my velocity?

 

It depends how fast he is traveling relative to you.

 

No, because I don't measure my second compared to HIS MOTION. I measure MY motion by measuring the distance and time traveled that I TRAVEL. It has nothing to do with his motion or position.

Edited June 19, 2008 by Motor Daddy
multiple post merged

[Sayonara]

Velocity is what d/t? What does another object have to do with my velocity?

Read around the links that have been posted. I am sure they explain it more concisely and effectively than I will; I will probably just make you more confused.

[Cap'n Refsmmat]

So when you measure the speed of light, since your second is different than mine, the light you measure actually travels a different distance in your second than when I measure the speed of light with my second?

No. Crazily enough, light always travels the same speed, regardless of how fast I'm moving. But if you were to fire a gun and measure the speed of its bullet, what you said may be true.

 

No, because I don't measure my second compared to HIS MOTION. I measure MY motion by measuring the distance and time traveled that I TRAVEL. It has nothing to do with his motion or position.

 

Correct. But you asked a question about how different our version of a "second" is, and DrP is also correct. Let me explain.

 

One common way of describing time is as a fourth dimension that we are constantly traveling through. Everyone moves "through" the time dimension. But whenever you begin to move through the other dimensions, you lose "speed" in the time dimension -- you essentially lose speed through time because you're speeding up in space. So you're going blazing fast through space but not quite as fast through time. Eventually, as you approach the speed of light through space, you're only inching through time.

 

Does that make a little more sense?

 

As Sayonara suggested, take a look at the links. Sisyphus' link covers some of this in better detail.

[Klaynos]

It depends how fast he is traveling relative to you.

 

And also on the frame that you measure it from...

[Motor Daddy]

No. Crazily enough, light always travels the same speed, regardless of how fast I'm moving. But if you were to fire a gun and measure the speed of its bullet, what you said may be true.

 

So when light travels at the same speed, that means it travels the same distance in the same time, correct? If you change the second does not light travel a different distance in that different second?

 

186,000 miles is a specific distance. If your second is different than mine, than light does not travel 186,000 miles in a second for you, which means your light travels at a different velocity, because your second is different.

 

 

 

Correct. But you asked a question about how different our version of a "second" is, and DrP is also correct. Let me explain.

 

One common way of describing time is as a fourth dimension that we are constantly traveling through. Everyone moves "through" the time dimension. But whenever you begin to move through the other dimensions, you lose "speed" in the time dimension -- you essentially lose speed through time because you're speeding up in space. So you're going blazing fast through space but not quite as fast through time. Eventually, as you approach the speed of light through space, you're only inching through time.

 

Does that make a little more sense?

 

As Sayonara suggested, take a look at the links. Sisyphus' link covers some of this in better detail.

 

We don't move through time, we move, and we measure the distance traveled against a standard of duration.

 

A velocity of 1 ft/sec for 1 second means a traveled distance of 1 ft. in the duration of 1 second.

 

A velocity of 10 ft/sec for 1 second means a traveled distance of 10 ft. in the duration of 1 second.

 

A velocity of 1,000 ft/sec for 1 second means a traveled distance of 1,000 ft. in the duration of 1 second.

 

A velocity of 1,000,000,000,000,000 miles/sec for 1 second means a traveled distance of 1,000,000,000,000,000 miles in the duration of 1 second.

[Klaynos]

Please, please read some of the links you've been provided on special relativity.

[Phi for All]

Thread closed temporarily to allow for some much needed link reading to take place.

 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

OK, thanks for the respite, I hope deep breaths were taken and links were thoroughly investigated. Please resume discussion.

Edited June 19, 2008 by Phi for All
multiple post merged

[Edtharan]

No, because I don't measure my second compared to HIS MOTION. I measure MY motion by measuring the distance and time traveled that I TRAVEL. It has nothing to do with his motion or position.

Ahh. Ok. I see this is where the source of your confusion lies.

 

Here is a question: Imagine that you are in empty space and nothing else exists. Can you tell me how fast you are travelling?

 

Against what can you measure how far you have moved?

 

Without something to compare your position with there is no way you can tell if you are moving (you can still tell if you are accelerating - but not if you are getting faster or getting slower).

 

Under constant velocity, without any point of reference, it is the same as if you are not moving at all.

 

Or think about this one: Sitting at your computer, how fast are you moving?

 

Well compared to the seat, you are not moving at all. Compared to the Moon you are moving at around 1.022 km/s.

 

Hang on. But you aren't moving compared to the Seat. How can you be simultaneously sitting (literally) still and also moving far faster than the speed of sound?

 

May be it is the Moon that is moving not us? But, what if there was someone on the Moon that was also sitting at a computer? Compared to the Moon they would not be moving, and compared to the Earth (you) they would be moving around 1.022 km/s.

 

How can you both be sitting still and both be moving?

 

Simple. All motion is Relative.

 

What does this mean? Well it means that there is no absolute measure of motion. There is nothing that all objects in the universe can compare their motion against and determine exactly how fast they are moving.

 

In relativity speak it is stated as: There is no preferred Frame of Reference.

 

Finally. Imagine you are in a space ship in empty space. Except now you see another space ship heading towards you. But wait, is it, or are you heading towards it? Which is it?

 

The other ship sees the same thing. Are you heading towards it or are they heading towards you?

 

Again, motion is relative so it means that both views are actually the same thing. Under the laws of Physics, it does not matter who is the one moving, only that there is motion relative to the other.

 

So, what does this mean?

 

In your statement I quoted: "I don't measure my second compared to HIS MOTION."

 

The reality is that you do. Remember all motion is relative, including motion through Time.

 

But why should that be?

 

Well, there is one thing about relativity: In all frames of reference the speed of light must remain constant. Now, as Velocity is Distance divided by Time, then these must change for it to be true. So either Distance, or Time or Both must change.

 

So if I was travelling at 99% of the speed of light (or around 297,000km/s), I must still see light travelling at 300,000km/s. But if you were sitting at your computer as I whizzed by you and made the same measurement of the speed of light at the same time, you would also conclude that light travels at 300,000km/s.

[Motor Daddy]

Ahh. Ok. I see this is where the source of your confusion lies.

Here is a question: Imagine that you are in empty space and nothing else exists. Can you tell me how fast you are travelling?

 

What is empty space?

Edited June 20, 2008 by Sayonara³
Cropped quote of entire post :rolleyes:

[swansont]

What is empty space?

 

Space with nothing else in it.

[nstansbury]

Here are some thought experiments that might help you begin to appreciate the ramifications of that fact:

 

Special Relativity Thought Experiments

 

That link provides some really interesting reading, Motor Daddy this is specifically relevant to this discussion:

 

"1. The Principle of Relativity: One cannot tell by any experiment whether one is at rest or moving uniformly (that is, moving in a straight line with constant velocity). In other words, there is no such thing as absolute rest. All motion or rest is only in relation to other observed objects (i.e. I can consider myself not to be moving with respect to the earth while at the same time I am moving very rapidly with respect to the sun)."

[Motor Daddy]

Space with nothing else in it.

 

 

Can you give an example of empty space, and how can it be empty space if I am there?

 

If I am the only object in empty space, where did I come from, and where did my space ship come from?

 

If I am traveling at a velocity, how did I get to that velocity? Did I accelerate to that velocity?

[nstansbury]

Can you give an example of empty space, and how can it be empty space if I am there?

 

A model spaceship in a vacuum chamber. There is still a vacuum - only it has a model spaceship in it.

 

MD - read experiments:

 

http://aether.lbl.gov/www/classes/p139/exp/experiment2.html

http://aether.lbl.gov/www/classes/p139/exp/experiment3.html

[Phi for All]

Can you give an example of empty space, and how can it be empty space if I am there?

 

If I am the only object in empty space, where did I come from, and where did my space ship come from?

 

If I am traveling at a velocity, how did I get to that velocity? Did I accelerate to that velocity?

I sense you are purposely missing the point of these examples.

[Edtharan]

What is empty space?

Exactly what it said: space that is empty.

 

If I am the only object in empty space, where did I come from, and where did my space ship come from?

It was a thought experiment. That is a simplified experiment done in your head to test or demonstrate a particular argument.

 

If I am traveling at a velocity, how did I get to that velocity? Did I accelerate to that velocity?

The bounds of the thought experiment did not include you getting to that speed. I was using the Thought Experiment to demonstrate relative motion at a constant speed. Acceleration is a completely different frame of reference and is not covered by special relativity (as in certain circumstances). For that you need General Relativity (as in it is applicable to a more situations that special relativity).

 

Actually, Einstein came up with Special Relativity first, but he knew that it didn't cover all situations. He released that theory knowing that it was incomplete and that he was going to work on a more General theory later. He them developed General Relativity to cover the holes in the Special Theory of Relativity.

 

You seem to be arguing that Special Relativity is incomplete. Well you are write. However General Relativity covers and explains all those holes.

 

You see, many people here have been getting frustrated because you point to a hole in Special relativity. However, they then say that that situation is not covered by Special relativity and that it is instead covered by General Relativity. You then ignore the fact that they situation is supposed to be covered in General Relativity and then keep pointing to the hole in the Special Theory.

 

It is a bit like how someone might point to the theory of gravity and claim that it doesn't explain how stars get their heat. Then someone responding to that by saying that stars don't get their heat from gravity, but get it instead by fusion. Then that first person jumping up and down saying that fusion is not part of the theory of gravity so it doesn't actually explain it.

 

So to reiterate: Acceleration is part of the General Theory of Relativity. I was talking about constant motion which is part of the Special Theory of Relativity.

 

Can you give an example of empty space,

Ok, Intergalactic space in the middle of one of the voids between galactic clusters. What is specifically meant was that there was no points of reference (as they would indicate relative motion) and you were far enough away from gravitational fields so that we didn't have to consider these into our reference frames (they complicated the situation a bit but they do act like an acceleration - and as we are not using General Relativity, these are unnecessary).

 

and how can it be empty space if I am there?

Ok, if you really wan to be pedantic...

 

Empty except for you. You were launched billions of billions of billions of years ago by linear acceleration with a counter weight sent in the opposite direction. You were in cryogenic sleep for the duration and you are wanting to determine where you came from or if you started here and everyone else left. Also if you are moving you want to know which direction you are moving in because then you will know how to get back.

 

There is no trace exhaust and no engines on the ship that might give you a hint at which direction you came from (you could always take a guess that the direction the ship came form is in the direction that the main engines are facing). The ship has no power to operate its sci-fi like sensors so you can only rely on you own eyes and simple sensors (like optical telescopes and computers).

 

Because it has been so long, all the stars have used up their fuel and have grown dim. So you can't use the light of the stars to determine you motion either. In fact the expansion of the universe has also accelerated and light beyond a few billion light years will never reach you. Also this expansion has reduced the the density of matter (other than you space ship) so that there would not be a single atom of any matter to be within that billion light years.

 

So, no matter, no light, no gravity, nothing except your ship (oh and mine, but you didn't see me at first as the window in you ship restricted your field of vision).

 

Is that clear enough for you?

[swansont]

Can you give an example of empty space, and how can it be empty space if I am there?

 

If I am the only object in empty space, where did I come from, and where did my space ship come from?

 

If I am traveling at a velocity, how did I get to that velocity? Did I accelerate to that velocity?

 

It's a thought experiment. You have meet us halfway on this.

[Sisyphus]

Can you give an example of empty space, and how can it be empty space if I am there?

 

If I am the only object in empty space, where did I come from, and where did my space ship come from?

 

If I am traveling at a velocity, how did I get to that velocity? Did I accelerate to that velocity?

 

You wake up in a spaceship. You have no idea how you got there. Looking out your windows, you see nothing whatsoever. As far as you can tell, you are in an infinitely large space with nothing in it except you and your spaceship.

[Motor Daddy]

OK, I'll play your imaginary, hypothetical, fairytale.

 

What is my initial velocity?

[ydoaPs]

OK, I'll play your imaginary, hypothetical, fairytale.

 

What is my initial velocity?

 

Relative to what?

[Motor Daddy]

Relative to what?

 

You set the rules, I am playing your game, remember?

[Cap'n Refsmmat]

I think the point of the game is that you have no idea what your initial velocity is, nor do you have any way of telling.

[swansont]

More train stuff moved to the other thread.

 

 

 

This is about the Rocket Ship