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Space and Time Can Warp Your Mind
Space
What is space?Gridwork for
measuring distances
Everything – planets, stars, galaxies, and the universe
Is space infinite?
Time
What is time?The constant drumbeat of existence“Time is what happens when nothing else
does.”
Measured with atomic clocks to one part in 1015
One second since the demise of the dinosaurs
Does time have a beginning? An end?
Motion
Change of position in space over timeChange in spaceChange in time
Motion through space variableMotion through time constantChange within fixed framework
Motion is Relative
Motion measured compared to fixed frame of referenceWhich frame is fixed? Which is moving?Why you can’t sit stillEarth’s rotation – 800 mphEarth’s orbit – 65,000 mphSun’s orbit – 450,000 mphMilky Way’s motion – 1,300,000 mph
Speed of Light
Speed of Light
Finite186,000 miles per second670 million mph
Light travel distancesEarth-Sun distance is 93 million miles500 seconds of light travel time1 light-year = 6 trillion miles
Time-Warped View
Proxima Centauri – 4.2 lyCenter of Milky Way – 27 thousand lyAndromeda galaxy – 2.5 million lyFornax cluster – 65 million lyMost distant objects – 13 billion ly
Looking out in space = back in time
Observable Universe
Finite speed of lightFinite age of the universeFinite volume observablePropertiesSphericalCentered on the observerHorizon, not edge
Special Theory of Relativity
Special Theory of Relativity
Speed of light is an absolute - cPhysics is the same to all observersObserver at restObserver in motionInertial reference frameOur reference frame has considerable
motion
Non-relativistic Motion
Velocities add together
20 mph
2 mph
Total 22 mph
Relativistic Motion
Motions don’t add linearly
0.95 c
0.1 c
Total 1.05 c - WRONG
Relativistic sum = 0.96 c(0.1 + 0.95) c(1 + 0.1*0.95)
Special Theory of Relativity
Thought experimentsDeduce relativistic behaviorObserver at rest vs. observer in motion
Speed of light is constantChange in space differentChange in time different
Thought Experiment - rest
light
mirror
Measure distanceMeasure timeCalculate speed of light
Thought Experiment - motionmirror
light
Measure distanceMeasure timeCalculate speed of light
Shrinking Space
Length contractionThe length of an object appears shorter
when measured by a moving observerSpaceship pilot flying at 0.99c would measure football field as 14 yards longCrowd would measure spaceship to be 1/7 as long as pilot thinksRelativistic diet tip: If you move fast, other people think you’re thinner
Stretching Time
Time dialationTime appears to slow down when
measured by a moving observer
Travel to Proxima Centauri at 0.99 c would take 4.25 yearsPilot would only age (4.25/7) years, about 7 monthsOne way time travel to the future
Light doesn’t exist?
At speed of light, lengths go to zeroAt speed of light, time stands stillPhoton of light doesn’t experience space or time Emitted Instantaneously crosses any amount of spaceAbsorbed
In its own frame of reference, light doesn’t exist in space or time
Special Theory of Relativity
One’s view of space and time depends on one’s motion
General Theory of Relativity
General Theory of Relativity
Matter warps spaceRe-interpret gravity as geometryStraight paths, but in curved spaceGeodesic
Extends special relativity to handle non-inertial frames of reference
Warped Space
Warped Space
Matter tells space how to curve
Curved space tells matter how to move
Gravitational Lenses
More mass, more warpWarped space can act like a glass lens
Slowing Time
Gravitational time dilationClocks run slower in a larger gravitational
fieldTested by flying atomic clock in planeSlower due to special relativityFaster due to general relativityToday’s atomic clocks can measure altitude difference of 1 yard
General Theory of Relativity
One’s view of space and time depends on how much matter is around and how it is distributed
Expansion of Space
Einstein’s Greatest Mistake
Equations for the universe unstableEinstein added an energy of space (cosmological constant) term to create stable solutionMissed predicting the expansion of the universe
Energy of motion
Energy of matter
Energy of space
= +
Expansion of Space
Hubble measured motions of galaxiesAll appear to move away from usCosmic cooties?
Expansion through space - WRONGGalaxies moving away from centerNo measurements show a centerCopernican hypothesis underlies
astronomy, and all science
Expansion of Space
• Expansion of spaceGalaxies at restSpace between galaxies expandingAll galaxies see every other galaxy moving
awayNo centerDifferent kind of relative motionObservers at restReference frame in motion
Big Bang
The Universe has expanded …from small to bigfrom hot to coldfrom dense to rarified
Standard framework of cosmologyOnly hypothesis that fits observationsScientific theory
Big Bang Observation
Cosmic Microwave BackgroundRemnant glow from hot early universe Seen in every direction on the sky\ Perfect thermal spectrumTime: half a million years after big bangTemperature: 3000 degrees Size: 1/1000th present size
Observational evidence that the universe was smaller, denser, and hotter in the past
Expansion of Space
One’s view of space and time depends on when in the history of the universe one is observing
SOME say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To know that for destruction ice
Is also great
And would suffice.
Fire and Ice - Robert Frost
“Thank You”