 Special Relativity
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 Podcast
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Intro
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For centuries, development of science was both fairly simple & intuitive. Classical ("Newtonian") physics developed on basis of everyday experience, observations of the world around us.
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In some situations (only available to humanity recently), classical physics breaks down -- situations that deal with the very small, or very big, or very fast.
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Turns out that classical physics is a special case -- take the equations of physics that have been derived more recently, drop out terms related to high speed / high acceleration, and classical physics drops out. Classical physics is essentially an approximation to a larger sense of reality.
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Modern physics is more accurate than the old way of seeing things, but it isn't exactly intuitive -- specifically since it deals with situations outside of our everyday experience.
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This episode is the first in a series on the topic of modern physics. This week -- special relativity. In subsequent episodes I'll talk about other facets of modern physics -- particularly, general relativity and quantum mechanics.
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Concepts we'll be messing with
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Space -- three dimensions that we're aware of (at least in our daily lives).
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Time -- in everyday experience, time separates events that occur in space.
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Mass & weight -- easy to use these interchangeably in daily life, but there's a difference, and they'll both show up in these discussions.
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Energy -- lots of forms in common experience: kinetic, thermal, electric, potential, etc. We'll be adding to this shortly.
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Light -- acts somewhat like a particle ("corpuscular" model), somewhat like a wave
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History -- briefly touched on in episode 4, let's go a bit deeper now...
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Aristotle (384 - 322 BC) -- absolute view of reference frames
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Galileo (1564-1642) -- introduced principle of relativity; held that uniform motion in a straight line only had meaning relative to something else. Also said there was no absolute reference frame by which all things could be measured.
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Newton (1643-1727) -- improved on Galileo in many ways, but still liked absolute reference frames, an "absolute space." Believed that light was corpuscular.
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Later physicists -- wave model of light more useful than corpuscular model. Since mechanical waves travel in a medium, was assumed that light did as well. "Luminiferous aether" -- implied existence of an absolute frame of reference.
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 1800's -- light, electricity, magnetism now understood as aspects of electric & magnetic fields.
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1900's -- a flurry of work early in the century breaks things open
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Two postulates -- principle of relativity, invariance of speed of light
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It's tough to separate time from space -- are symbiotic. Events occur in space & time -- thus a new concept: spacetime (a.k.a. spacetime continuum). In this view of things, time is essentially a 4th dimension, scaled (w.r.t. spacial dimensions) via the speed of light.
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Consequences -- Lorentz' transformations, and with them Special Relativity, lead to different physical predictions than Newtonian mechanics when relative velocities become comparable to the speed of light. The speed of light is so much larger than anything humans encounter that some of the effects predicted by relativity are initially counter-intuitive:
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Time dilation
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Lack of absolute simultaneity
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Lorentz contraction
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Addition of velocities
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Mass and momentum
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Wrapup
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Special relativity is mathematically self-consistent, and is also compatible with all modern physical theories, However special relativity is incompatible with several earlier theories, most notably Newtonian mechanics -- at least in certain regimes.
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A number of experiments have been conducted to test special relativity against rival theories. Has survived everything we've thrown at it so far
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In addition, particle accelerators run almost every day somewhere in the world, and routinely accelerate and measure the properties of particles moving at near lightspeed. Many effects seen in particle accelerators are absolutely consistent with relativity theory and are grossly inconsistent with the earlier Newtonian mechanics.
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Impacts of SR not entirely absent from regular life
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Sources and other links
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Relativity in general
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Special Relativity
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Keywords -- special relativity physics Einstein time dilation Lorentz contraction
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License The use of these shownotes is governed by a Creative Commons (Attribution-NonCommercial-ShareAlike 2.5) license
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