Another speed of light question

[orgmark]

Say I'm in a spaceship traveling 0.999999999999999 c
I'm a bit curious as to how I got going that fast. I at this
point decide someone should be steering the ship. I
walk form the back of the ship to the front. What
happens when I attempt to do this?

 

[Integral]

You arrive at the back of the ship, turn around and walk to the front. Meanwhile you note that since the food is so terrible, not only is your mass not nearing infinite, you have actually lost weight.

 

[phja]

basically, everything would apear normal from your point of view (referance frame). you could walk around just like you can on earth. in fact the only way you can deduce you are moving at 99.99999% speed of light is to compare it to another referance frame but even then you don't know if your moving at this speed, or the comparitive referance frame is.

so, absolute motion cannot be detected without something to compare it to. eg- the only way to know your aeroplane is moving is to look down at the ground.

 

[Fredrik]

If you are concerned that your walking speed v should be added to the ship's speed u to get the total speed u+v, which may be >c, then the answer is that your speed in the frame where the ship is moving with speed v isn't u+v, it's (u+v)/(1+uv/c²) and that's always <c unless u=v=c.

 

[phja]

exactly, and from your perspective, your only moving at walking speed, the ship isn't even moving (well, you can't determine if it's moving without an outside referance frame, so you are completely valid in saying the ships not moving).

 

[DaveC426913]

The key points from all the above arguments are:
1] within that reference frame, nothing is out the ordinary, time passes as usual; there is no way to claim that the observer is doing any speed; he might as well be stopped and the planets are rushing past him
2] relativistic velocities do not simply add. In a very sloppy nutshell, 0.99999c+0.00001c does NOT equal 1.0c, it equals 0.999990000...01c.

 

[orgmark]

Doesn't an object's mass increase as it approaches the speed of
light? Would I be able walk to the front of the ship if my mass
was infinite? I have read enormous amounts of energy are required
to accelerate an object moving at these velocities.

 

[DaveC426913]

Doesn't an object's mass increase as it approaches the speed of
light? Would I be able walk to the front of the ship if my mass
was infinite? I have read enormous amounts of energy are required
to accelerate an object moving at these velocities.

Again, the observer will experience nothing untoward. It is only when compared to an external frame of reference that the changes will be apparent.

 

[MeJennifer]

You arrive at the back of the ship, turn around and walk to the front. Meanwhile you note that since the food is so terrible, not only is your mass not nearing infinite, you have actually lost weight.

 

[russ_watters]

Doesn't an object's mass increase as it approaches the speed of
light?

Your speed with respect to yourself is zero and is always zero. So you never notice any mass increase.

 

[MeJennifer]

Indeed the proper mass, an Lorentz invarant quantity by the way, does not depend on relative speed. Relativistic mass however does but this quantity is not Lorentz invariant.

 

[Nickelodeon]

I
walk form the back of the ship to the front. What
happens when I attempt to do this?

I would have thought that you would find it extremely difficult to walk to the front due to huge energy requirements to do so. If you happened to be at the front and walked to the back then you would find it easy.

 

[Dale]

It doesn't take a greater-than-normal amount of energy in your own frame.

 

[DaveC426913]

I would have thought that you would find it extremely difficult to walk to the front due to huge energy requirements to do so. If you happened to be at the front and walked to the back then you would find it easy.

You and I are on a spaceship called Earth, which is moving at .99c relative to something. This is identical to the siutation in the smaller spaceship. We don't find it harder to move West than East.

 

[Nickelodeon]

You and I are on a spaceship called Earth, which is moving at .99c relative to something. This is identical to the siutation in the smaller spaceship. We don't find it harder to move West than East.

Agreed, but we do find it more difficult to go up rather than down and that is the "something" that we are relative with in our reference frame

 

[Nickelodeon]

It doesn't take a greater-than-normal amount of energy in your own frame.

Could there be any chance that reference frames are specific to the region of space that you are in at the time? In this scenario, you are pushing your own frame through the natural regional specific frame which resists anything trying to go faster than 'c'

 

[Dale]

Could there be any chance that reference frames are specific to the region of space that you are in at the time? In this scenario, you are pushing your own frame through the natural regional specific frame which resists anything trying to go faster than 'c'

A reference frame is nothing more than a coordinate system, it is a useful mathematical tool, not a physical entity. There is no such thing as a "natural frame", and mathematical tools don't "resist" things.

The whole point of relativity is that the laws of physics are the same in any reference frame. In other words, you can choose whatever coordinate system you like, you will obtain all of the same experimental outcomes.

 

[matheinste]

Hello Nickllodeon.

Quote:-

----Agreed, but we do find it more difficult to go up rather than down and that is the "something" that we are relative with in our reference frame -----

Don't forget up and down are themselves relative. In the case of the earth, an upward pointing vector relative to the Earth's surface remains a downward pointing vector relative to the Earth but relative to te sun it will chang direction and points in another direction as the eargth moves relative to the sun. Up and down are relative to the Earth's surface in our normal use of the words. Roughly speaking, take a vector pointing at the sun at mid day, we call it upward pointing. Take the same vector at midnight, still pointing towards the now invisible sun, we would then call this same vector downwards, pointing in the Earth's frame. Of course a vector pointing directly towards the Earth's centre, downwards, remains so at all times. We find moving upwards along this upward pointing vector, with respect to the earth, more difficult because gravity is "acting" in our downward direction all the time. The wording may not be quite rigorous but i am sure will get the idea.

In the case of the spacecraft , movement within it forward and back, up or down has no relevance if there is no force acting upon it, which will be the case in an inertial frame.

Matheinste.

 

[Nickelodeon]

A reference frame is nothing more than a coordinate system, it is a useful mathematical tool, not a physical entity. There is no such thing as a "natural frame", and mathematical tools don't "resist" things.

The whole point of relativity is that the laws of physics are the same in any reference frame. In other words, you can choose whatever coordinate system you like, you will obtain all of the same experimental outcomes.

So what is stopping orgmark going faster than light as he walks to the front of the spaceship?

 

[Varnick]

The relativistic formula for velocity addition is different to Newtonian Mechanics, preventing a speed ever being equal to C.

v_1 + v_2 \neq v_3

 

[ZapperZ]

So what is stopping orgmark going faster than light as he walks to the front of the spaceship?

May I suggest you and the OP check the hyperphysics webpage first and see if you can understand the description given there.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html#c2

Note how, for v<<c (i.e. our "normal" situation), we get back our beloved rule for velocity addition. This shows that our regular velocity addition is only a "special case" for a more generalized description on how we add velocity.

Zz.

 

[Dale]

So what is stopping orgmark going faster than light as he walks to the front of the spaceship?

ZapperZ is correct. It is not that it would take the guy too much energy to walk to the front of the spaceship, it is simply a result of the Minkowski geometry of spacetime. In Minkowski geometry velocities add such that the velocity is always less than c in any frame, regardless of how fast the ship is going in that frame or how fast he is walking in the ship's frame.

 

[Nickelodeon]

May I suggest you and the OP check the hyperphysics webpage first and see if you can understand the description given there.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html#c2

Note how, for v<<c (i.e. our "normal" situation), we get back our beloved rule for velocity addition. This shows that our regular velocity addition is only a "special case" for a more generalized description on how we add velocity.

Zz.

The examples given talk about observed phenomena at high speeds. Velocity measurement is governed by the time information takes to reach us so no way will any object be observed going faster than light in any direction it happens to be moving.
I think the problem comes when switching from observed speeds to real speeds. Are you sure the two need necessarily be the same?

 

[Dale]

I think the problem comes when switching from observed speeds to real speeds. Are you sure the two need necessarily be the same?

You misunderstand relativity. All of the relativistic effects remain even after accounting for the finite travel time of light.

Relativity is not about optical illusions, and all observers are considered intelligent enough to realize that the time that they receive a distant light signal is not the same as the time that the signal was emitted, and correctly account for the delay.

 

[Nickelodeon]

You misunderstand relativity. All of the relativistic effects remain even after accounting for the finite travel time of light.

Relativity is not about optical illusions, and all observers are considered intelligent enough to realize that the time that they receive a distant light signal is not the same as the time that the signal was emitted, and correctly account for the delay.

So if relativistic effects remain, then the pilot's mass will be approaching infinity in reality. Presumably, the energy required to accelerate him and get him to the front of the spaceship will also be approaching infinity. This is not what you infered (or I interpreted) in one of your previous threads. eg.

ZapperZ is correct. It is not that it would take the guy too much energy to walk to the front of the spaceship, it is simply a result of the Minkowski geometry of spacetime.

 

[Dale]

This is one reason why I don't like the concept of "relativistic mass". I never use that concept myself and I do not recommend its use.

When most modern physicists speak of mass they mean the Minkowski norm of the http://en.wikipedia.org/wiki/Four-momentum" , which is a Lorentz invariant. The pilot's mass is most definitely not increasing in the pilot's frame and therefore, for the pilot it does not take any more effort to walk to the front than normal.

 

[lightarrow]

So if relativistic effects remain, then the pilot's mass will be approaching infinity in reality. Presumably, the energy required to accelerate him and get him to the front of the spaceship will also be approaching infinity.

I'm in the ref. frame of a beam of neutrinos close to the Earth; I'm seeing you, in this exactly moment, traveling past me at 0.999999999c. Let me have a precise look: ...hmm...no, no, your mass doesn't seem very different from usual (unless you ate too many ice creams in the last hours...).
What they wrote you is the reality, not theories. Re-read them and if it's not enough, do it again.

 

[DaveC426913]

So if relativistic effects remain, then the pilot's mass will be approaching infinity in reality.

Stop right there.

There is no such thing is an objective frame of reference. There is no "reality versus "less than reality" in the sense you mean it.

The whole point of relativity - the very core - is exactly this: no frame of reference is preferred over any other. i.e. the pilot's frame of reference is equally valid. As far as he's concerned, he is stationary and the rest of the universe is moving. If he looked out his window, he'd see the Earth whizzing past him at .99c. If he measured the mass of a guy walking around on Earth, he'd measure the guy's mass as very high and would wonder how the guy can walk around at all.

Neither of them is wrong. Neither of the is seeing an illusion. Neither of their experiences are any less real.

 

[DaveC426913]

Let me have a precise look: ...hmm...no, no, your mass doesn't seem very different from usual

Actually, it would.

 

[lightarrow]

Actually, it would.

Are you talking about invariant mass?