Distance and Time and Special Relativity - Freaky Fzx Friday

The experiment from our last installment of Freaky Fzx Friday was high precision.  Extremely high precision.  So good that we knew without a doubt that all observers in the universe measure light speed to be the same no matter what the source or observer are doing.

Imagine that my aging arm can put out some HEAT



and you're waiting for a PAT bus at the corner of Fifth.  I'm in a bus traveling past you at 50 mph and I throw my amazing fastball toward the front of the bus.  What speed do you measure for the ball?

It has to be greater than 50 mph since the bus is already moving so you just add the speeds and get 150 mph forward.

Now I'm at the front of the bus, distracting the driver, and I see a misbehaving student in the back seat.  I take my fastball and send it in her direction.  What speed does she measure?  100 mph.  What speed do you measure as you record the whole thing with your iPhone to forward to the authorities and the media?

50 mph backward.

It turns out that the same principle works with sound waves in my enclosed bus.  You would just add or subtract the velocities, depending on the situation.

Later, in another bus, with different bus driver and a laser gun, we perform the same experiment and you're still waiting for the bus.

Proper Gangsta Grip for Accuracy

I always measure that light to travel at 186,000 mph.

The new bus is moving 100,000 mph.  What speed do I measure for the light beam?  186,000 mph.  What speed do you measure as I pass on the corner at 100,000 mph?

Nope. You measure 186,000 mph.  It is NOT the sum of the speeds this time.

Now let's do it again but in a different direction.  I still measure 186,000 mph.  What speed do you measure?  (And how many style points do I get?)

Crap.  Still 186,000 mph!  What's going on?  

Light does not act like the baseball and we cannot just add or subtract velocities.  Lorentz had already proposed his transformations.  It was Einstein who put it all together and explained it after almost two decades of the best minds working on the problem.

1) while moving at different speeds we measure distance and time differently.  But everybody measures everybody else's distance and time to be different.

2) and everybody's correct.  There is no absolute time or space.  Time and distance ARE different depending on your relative speed.

Freaky.  Next time, Simultaneity and Twins.

Speed of Light - Freaky Fzx Friday Introduction

A normal Fzx course rarely deals with the wonderful aspects of science discovered after the American Civil War.

I instituted Freaky Fzx Friday two years ago to give a bit of modern physics on a regular basis.

Todays topic - the speed of light.  Light is fast and difficult to measure.  After Galileo observed the moons of Jupiter, Roemer measured the speed of light using the orbit of Io in 1676.

Light travels at 186,000 miles every SECOND.  Ridiculous and far faster than Earth at at 65,000 miles per HOUR around the sun.

But by 1887, Michelson and Morley had precise instruments capable of measuring tiny differences in the speed of light.  They tried to detect the stationary background of space by comparing the speed of light parallel to and perpendicular to the motion of Earth around our Sun.

There was ZERO DIFFERENCE between the two speeds.  They checked their instruments and repeated the experiment to no avail.  It seemed that light has the same speed no matter its direction or the speed of the source..

Next time - Einstein's interpretation of the results.