Weird physics question - relativistic immobility

[KrazyHorse]

I find it interesting how Ali and KH managed to exchange 15 posts between each over before removing the other from their ignore lists.

"This user is on your ignore list. Click here yadda yadda yadda"

[KrazyHorse]

With the thread title I pretty much couldn't resist.

Also, for those who are interested I just found out that the COBE data isn't in HEALpix after all, but some bastard tesselation without HEALpix's nice qualities.

It's funny when you realize that all the elegant solutions you com upon in research level physics were NOT simply obvious to everybody from the start, but took many years to develop. Makes you feel less stupid.

[Blaupanzer]

Can an object (of whatever size) be "motionless" in the universe? Or does relativism dictate that we would imply motion as observers. I know the earth revolves around the sun at a certain speed compounded by the suns motion as a part of the galaxy and the galaxy's motion in the universe. This compounds to a seemingly high speed of motion. If we launch a ship with sufficient power to achieve escape velocity, it will be traveling at a speed near that of the earth initially. All the rocket jocks talk about speeding the ship up to near the speed of light to enable minimum time voyages out of the solar system. Couldn't the ship slow down as well? Could it slow to zero?

[Kuciwalker]

Can an object (of whatever size) be "motionless" in the universe?

No, you can only be motionless relative to a frame of reference. The entire point of relativity is that there is no absolute frame of reference that everything should be measured against.

[Blaupanzer]

Which was my second sentence. But what is the reference for the speeds we quote in our own motion? Relative to us, it is everyone else that's moving. However, that ship question arises. If it can "speed" up, then it can slow down. In that context, can it slow to zero? This is a guage question too, a how to calibrate question.

[KrazyHorse]

I have no idea what you're blathering about.

[Kuciwalker]

Which was my second sentence. But what is the reference for the speeds we quote in our own motion? Relative to us, it is everyone else that's moving. However, that ship question arises. If it can "speed" up, then it can slow down. In that context, can it slow to zero? This is a guage question too, a how to calibrate question.

What?

"Speeding up" and "slowing down" only make sense relative to a particular reference frame (e.g. the Earth). They are completely meaningless without one.

[Kuciwalker]

"Accelerate to near the speed of light" implicitly is "relative to the Earth".

[Blaupanzer]

We say a ship can speed up using various theoretical processes to approach speeds near the speed of light. (That sounds very much like a speedometer-type measure a speed inherent in the vehicle.) We are also provided with an explanation about how we cannot go faster than the speed of light (again making it sound like the measured speed is inherent in the object, not relative.)

If the first paragraph is not nonsense, then a ship that can speed up could also slow down. when slowing, could it approach a speed of zero in the same way it could approach the speed of light?

[Blaupanzer]

If we switch our object of relation, i.e., to the target planet, can we go faster than light when viewed from earth?

I am not unaware of the science guys. The speed of light is a constant. It is not as relative to the earth.

[KrazyHorse]

We say a ship can speed up using various theoretical processes to approach speeds near the speed of light. (That sounds very much like a speedometer-type measure a speed inherent in the vehicle.) We are also provided with an explanation about how we cannot go faster than the speed of light (again making it sound like the measured speed is inherent in the object, not relative.)

If the first paragraph is not nonsense, then a ship that can speed up could also slow down. when slowing, could it approach a speed of zero in the same way it could approach the speed of light?

The first paragraph is nonsense.

[Sirotnikov]

"Accelerate to near the speed of light" implicitly is "relative to the Earth".

I think you're wrong, or maybe you used the term accelerate improperly.

Movement at constant speed is indeed relative to your frame of reference. Acceleration requires a constant application of force. Acceleration is actual in all frames of reference, no matter how they measure your speed.

Especially when you move at the speed of light - you move at the speed of light period, regardless of frame of reference.

KH will soon show up to correct us both.

[Kuciwalker]

We say a ship can speed up using various theoretical processes to approach speeds near the speed of light. (That sounds very much like a speedometer-type measure a speed inherent in the vehicle.) We are also provided with an explanation about how we cannot go faster than the speed of light (again making it sound like the measured speed is inherent in the object, not relative.)

If the first paragraph is not nonsense, then a ship that can speed up could also slow down. when slowing, could it approach a speed of zero in the same way it could approach the speed of light?

All speeds are relative.

Your speed relative to any object can never exceed the speed of light.

The mathematics that resolves this [seeming, from a Newtonian POV] contradiction is called special relativity.

[Kuciwalker]

I think you're wrong, or maybe you used the term accelerate improperly.

Movement at constant speed is indeed relative to your frame of reference. Acceleration requires a constant application of force. Acceleration is actual in all frames of reference, no matter how they measure your speed.

I can accelerate at 1G forever and my velocity in my own reference frame remains 0. But if I say "accelerate to near the speed of light" then I must specify some other reference frame.

Especially when you move at the speed of light - you move at the speed of light period, regardless of frame of reference.

No, not 'regardless'. The key observation that leads to special relativity is that if you are moving at the speed of light relative to one reference frame, you are moving at the speed of light relative to all reference frames.

[KrazyHorse]

a) In special relativity, acceleration is not relative. In general relativity it is
b) Kuci's statement reads perfectly fine to me. The relative part is the part where you're going "near the speed of light". Also, colloquially acceleration implies that velocity is increasing. Which would make acceleration/deceleration relative. According to some other observer the spaceship starts out going near the speed of light and then slows to 0.