Today's lecture topic
- Thread starter ExCyber
- Start date
I remember studying this a long time ago... this demonstrates the problem with newtonian physics depending on who is observing the movement (or lack thereof).
Though, principally speaking, we're always constantly moving if we're sitting still, as the earth is rotating on it's axis and at the same time rotating around the sun. So philosophically, wouldn't it be easy enough to say 'regardless what you're doing, here on earth you're always moving at a uniform speed'?
Quite a cop out answer, I know.
Though, principally speaking, we're always constantly moving if we're sitting still, as the earth is rotating on it's axis and at the same time rotating around the sun. So philosophically, wouldn't it be easy enough to say 'regardless what you're doing, here on earth you're always moving at a uniform speed'?
Quite a cop out answer, I know.
Only somewhat a cop-out answer. I would have to agree with you I think.
Considering the question was about devising an experiment, I would have to agree that it is impossible simply because the experiment itself is also moving and that movement cannot be controlled for the reasons MTXBlau mentioned.
I added a cop-out to the cop-out, yay.
Considering the question was about devising an experiment, I would have to agree that it is impossible simply because the experiment itself is also moving and that movement cannot be controlled for the reasons MTXBlau mentioned.
I added a cop-out to the cop-out, yay.
This refers to "frames of reference". You and your experiment and everything you can see is part of a frame of reference, and the entire frame could be at rest or have constant velocity.
But what is at rest? At rest assumes that there is a central frame of reference, against which other frames can be measured, which contracts the theory of relativity. Nothing can be at rest, and nothing has inherent motion. Only relative measurements can be made.
That's the easy part to understand. The part I'm having trouble with seems to contradict it.
If frame B accelerates away from frame A at near the speed of light, and then stops, and accelerates back towards frame A, the calculations say frame B has experienced less time passage than frame A when they meet again.
But my question is, how do you know which frame is accelerating? You do you know that frame B is accelerating away from frame A, and not the other way around? Then you'd have a contradiction.
If a spaceship accelerates off of Earth, how do we know that the solar system isn't accelerating away from the spaceship? What defines that frame?
But what is at rest? At rest assumes that there is a central frame of reference, against which other frames can be measured, which contracts the theory of relativity. Nothing can be at rest, and nothing has inherent motion. Only relative measurements can be made.
That's the easy part to understand. The part I'm having trouble with seems to contradict it.
If frame B accelerates away from frame A at near the speed of light, and then stops, and accelerates back towards frame A, the calculations say frame B has experienced less time passage than frame A when they meet again.
But my question is, how do you know which frame is accelerating? You do you know that frame B is accelerating away from frame A, and not the other way around? Then you'd have a contradiction.
If a spaceship accelerates off of Earth, how do we know that the solar system isn't accelerating away from the spaceship? What defines that frame?
What you're describing is essentially the "twin paradox". I don't fully remember the explanation of it, but there is basically some kind of trick to it. There are several ways to explain it but IIRC the easiest example to understand and calculate is to suppose that each frame is sending light pulses to the other and calculate the relativistic Doppler shift on each leg of the trip.
The Twins Paradox is only a paradox if you assume that the earth brother and astronaut sister both see the travel as the same distance, but it isn't.
Since the sister is traveling at 0.6*c, space is compressed, and alpha centuri, 4-light-years away, appears to only be 3.2-light-years-away frm the sister's point of view. But it is still 4 light-years away from the brother's point of view. This is how the sister ages less.
The twins paradox assumes 3 points: a brother and a destination fixed at 4 light years away, and a sister that moves between them. However, here's how I think I create the contradiction, by adding a 3rd point to make the problem symmetrical.
Pretend instead there are two trains that a 4 light-years long, parallel to each other, facing in opposite directions. The sister train's engine starts next to brother train's engine:
CSSSE (sister train)
EBBBC (brother train)
Now, in the traditional twins paradox, Sister's engine (E) begins at brother's engine (E), and moves towards brother's caboose (C) 4 light years away. And then comes back.
From the solution to the twins paradox, sister's engine (E) ages 128 months, while brother's engine (E) ages 160 months. But now I've thrown in sister's caboose (C), which makes this symmetrical.
And this brings out the acceleration question. If sister's train was the one accelerating and deaccelerating, then the sister's train is not always in an inertial frame, while the brother's train always is, and the scenario is not symmetrical, and this is how the normal equation is played out. But how do you know which train is accelerating? Is acceleration symmetrical?
Since acceleration is caused by a force, and forces act in equal and opposite directions, shouldn't it be symmetrical?
Since the sister is traveling at 0.6*c, space is compressed, and alpha centuri, 4-light-years away, appears to only be 3.2-light-years-away frm the sister's point of view. But it is still 4 light-years away from the brother's point of view. This is how the sister ages less.
The twins paradox assumes 3 points: a brother and a destination fixed at 4 light years away, and a sister that moves between them. However, here's how I think I create the contradiction, by adding a 3rd point to make the problem symmetrical.
Pretend instead there are two trains that a 4 light-years long, parallel to each other, facing in opposite directions. The sister train's engine starts next to brother train's engine:
CSSSE (sister train)
EBBBC (brother train)
Now, in the traditional twins paradox, Sister's engine (E) begins at brother's engine (E), and moves towards brother's caboose (C) 4 light years away. And then comes back.
From the solution to the twins paradox, sister's engine (E) ages 128 months, while brother's engine (E) ages 160 months. But now I've thrown in sister's caboose (C), which makes this symmetrical.
And this brings out the acceleration question. If sister's train was the one accelerating and deaccelerating, then the sister's train is not always in an inertial frame, while the brother's train always is, and the scenario is not symmetrical, and this is how the normal equation is played out. But how do you know which train is accelerating? Is acceleration symmetrical?
Since acceleration is caused by a force, and forces act in equal and opposite directions, shouldn't it be symmetrical?
Kuta said:
To see what I mean, take a look at:
http://dictionary.reference.com/search?q=sound
You're both right.
It actually just depends on the definition of sound. For example, if you take the first meaning from the definition, MTXBlau is right. The sound doesn't exist because the definition of a "sound" is someone hearing something. If you take the second more technical meaning, it does exist as a sound as it isn't required to be heard.
MasterAkumaMatata
Established Member
ExCyber said:
True.
End of discussion.
Kuta said:
There's the very mechanical, mundane definition that dibz alluded to, and then there's the philosophical question - without someone to observe, does it exist?
Of course, science is based on verifiable, repeatable instances which lend credence to the notion that yes, there should be a sound. But this is based on the premise of what has been observed and a good faith belief while not observed, it will still make the same sound.
Though, much like the question that started all this, it's impossible to test.
