What Motions am I experiencing?

[Poimandres]

According to Einstein, the sum total of all of my motion equals the speed of light. With that in mind, I would like to know what types of motion I am experiencing as I sit here at my desk. I know that I am traveling through time, that the Earth is spinning on its axis, that the Earth is orbiting the Sun, that the sun is orbiting the Galactic Centre, that the Milky Way Galaxy is in some form of motion, and that the Universe is expanding. Is that all correct? Have I missed anything? Does the expansion of the Universe count as a type of motion that I am experiencing?

[mathematic]

"According to Einstein, the sum total of all of my motion equals the speed of light."

 

Where did you get that idea?????

[Poimandres]

Where did you get that idea?????

 

It's a tenet of Special Relativity.

[swansont]

It's a tenet of Special Relativity.

 

The postulates of relativity are that c is a constant and that physics is the same in all inertial reference frames.

 

One ramification is that the length of your velocity four-vector is invariant, and has a value of c. That's not quite the same as saying the sum of your motions is c; the four vector includes a time component. But another ramification is that if you aren't accelerating, you can always assume you are at rest.

[Poimandres]

The postulates of relativity are that c is a constant and that physics is the same in all inertial reference frames.

 

One ramification is that the length of your velocity four-vector is invariant, and has a value of c. That's not quite the same as saying the sum of your motions is c; the four vector includes a time component. But another ramification is that if you aren't accelerating, you can always assume you are at rest.

 

Thanks, swansont. But can you please explain that in layman terms? Please remember that I have no background in physics.

 

Isn't the sum of all of my motions c? And what's a four-vector?

[swansont]

Thanks, swansont. But can you please explain that in layman terms? Please remember that I have no background in physics.

 

Isn't the sum of all of my motions c? And what's a four-vector?

A vector has a magnitude and direction, or can be viewed as the orthogonal (mutually perpendicular) components. A four-vector is a vector that has three spatial components along with a fourth component which depends on time; in this case it tells you how much your time is being dilated in that frame of reference. They are useful in relativity because the lengths of the vectors contain pertinent information http://en.wikipedia.org/wiki/Four-vector

 

The length of the velocity four-vector is always c. Colloquially, your speed through spacetime is always c, where you've included how fast time is passing as a fraction of c.