Register to reply

Can you determine absolute motion?

by Physicist1231
Tags: absolute, determine, motion
Share this thread:
harrylin
#127
May15-11, 06:14 AM
P: 3,187
Quote Quote by Physicist1231 View Post
[..] I am still trying to find out how (and what) experiments were done that prove that Light approaches any reference point at C instead of C-V. [..]
Hi Physicist1231,
Was your first post of this thread sufficiently answered?

Assuming that relativity is correct, "The Omnipotent Point of view" cannot be disproved by experiments - as JesseM also mentioned. Perhaps because it has no practical use (how could we use a view that we can't determine!), it's less well known from the peer reviewed literature.

Relativity jargon is positivistic: only operational definitions are used, based on phenomena (appearances). Now, "Light approaches any reference point at C" is poorly stated, and therefore true or false depending on your references. The approaching speed of light is "relative" to the used reference system: it is set by definition equal to the receding speed in special relativity. You can read the definition here, in section 1:
http://www.fourmilab.ch/etexts/einstein/specrel/www/

As a result, the (apparent) "closing" or "approaching" speed has been made c wrt a reference point that is at rest in the reference system that you use, by appropriately regulating the clocks (see also Einstein 1907, Jahrbuch Radioelectr. Electr.4, 414).
It seems that you correctly understood that it is not c relative to a point that is "moving" in your reference system - indeed, that would be paradoxical, as the vector subtraction (c-v) with c=constant and v=/=0 cannot equal c.

The impossibility to determine absolute motion (in the original, Newtonian sense) is directly related to the impossibility to determine the absolute one-way closing speed of light, which in turn is directly related to relativity of simultaneity.

Harald
xxxx0xxxx
#128
May16-11, 12:04 PM
P: 68
Quote Quote by rede96 View Post
I was thinking that if I was to use lateral thrusters, the amount of thrust I would need to turn the ship 90 degrees would depend on the speed I was travelling. The faster I was going the more thrust I need.

Something like it takes more force to change the direction of moving object then a static one, as a moving object’s mass increases. (E= mc2) the faster it goes. So if it took more force to change direction then I must have gathered more than my rest mass and thus must be ‘moving’
The force required to change direction is applied in your rest frame, and is independent of relative motion. For you, your mass is always your rest mass. For others not at rest with you, you have additional energy/mass in the form of momentum.

Your thrusters do not change your net momentum, since they only produce angular acceleration (you do lose rest mass however).
chingel
#129
May17-11, 07:49 AM
P: 261
But can you determine absolute rotation? The further away you go on a merry-go-around the harder it tries to throw you out. If the universe is spinning around a center, can we absolutely determine by how much?
DaleSpam
#130
May17-11, 12:30 PM
Mentor
P: 17,308
Quote Quote by chingel View Post
But can you determine absolute rotation?
Yes. Rotation is a non-inertial motion.
xxxx0xxxx
#131
May17-11, 12:37 PM
P: 68
Quote Quote by chingel View Post
But can you determine absolute rotation? The further away you go on a merry-go-around the harder it tries to throw you out. If the universe is spinning around a center, can we absolutely determine by how much?
Well, from the point of view of the moon, earth rotates around it, and I would say the universe rotates around us every 24 hours :)

If you are within some sort of rotating structure, you will experience centripetal force if you appear to be stationary with the structure, and you will observe coriolis motion of objects moving relative to the structure; otherwise the interior structure will be moving with respect to you in a circle ... and yes these would be measurable absolute effects.


Register to reply

Related Discussions
Detecting absolute motion? Special & General Relativity 52
Determine the angular frequency w where the absolute value of the input impedance is Engineering, Comp Sci, & Technology Homework 5
Detecting absolute motion Special & General Relativity 94
Absolute Motion? Special & General Relativity 14
Orbit and absolute motion General Physics 3