Space and Time Can Warp Your Mind Frank Summers Space Telescope Science Institute June 3, 2003

Fundamental Framework

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 One second since the demise of the dinosaurs Does time have a beginning? An end?

Motion Change of position in space over time Change in space Change in time Motion through space variable Motion through time constant Change within fixed framework

Motion is Relative Motion measured compared to fixed frame of reference Which frame is fixed? Which is moving? Why you can’t sit still Earth’s rotation – 800 mph Earth’s orbit – 65,000 mph Sun’s orbit – 450,000 mph Milky Way’s motion – 1,300,000 mph

Speed of Light

Finite 186,000 miles per second 670 million mph Light travel distances Earth-Sun distance is 93 million miles 500 seconds of light travel time 1 light-year = 186,000*60*60*24* light-year = 6 trillion miles

Time-Warped View Proxima Centauri – 4.2 ly Center of Milky Way – 27 thousand ly Andromeda galaxy – 2.5 million ly Fornax cluster – 65 million ly Most distant objects – 13 billion ly Looking out in space = back in time

Observable Universe Finite speed of light Finite age of the universe Finite volume observable Properties Spherical Centered on the observer Horizon, not edge

Special Theory of Relativity

Speed of light is an absolute - c Physics is the same to all observers Observer at rest Observer in motion Inertial reference frame Our 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 ( ) c ( *0.95)

Special Theory of Relativity Thought experiments Deduce relativistic behavior Observer at rest vs. observer in motion Speed of light is constant Change in space different Change in time different

Thought Experiment - rest light mirror Measure distance Measure time Calculate speed of light

Thought Experiment - motion mirror light Measure distance Measure time Calculate speed of light

Shrinking Space Length contraction The length of an object appears shorter when measured by a moving observer Spaceship pilot flying at 0.99c would measure football field as 14 yards long Crowd would measure spaceship to be 1/7 as long as pilot thinks Relativistic diet tip: If you move fast, other people think you’re thinner

Stretching Time Time dialation Time appears to slow down when measured by a moving observer Travel to Proxima Centauri at 0.99 c would take 4.25 years Pilot would only age (4.25/7) years, about 7 months One way time travel to the future

Light doesn’t exist? At speed of light, lengths go to zero At speed of light, time stands still Photon of light doesn’t experience space or time Emitted Instantaneously crosses any amount of space Absorbed 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

Matter warps space Re-interpret gravity as geometry Straight paths, but in curved space Geodesic Extends special relativity to handle non-inertial frames of reference

Warped Space

Matter tells space how to curve Curved space tells matter how to move

Gravitational Lenses More mass, more warp Warped space can act like a glass lens

Slowing Time Gravitational time dilation Clocks run slower in a larger gravitational field Tested by flying atomic clock in plane Slower due to special relativity Faster due to general relativity Today’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 unstable Einstein added an energy of space (cosmological constant) term to create stable solution Missed predicting the expansion of the universe Energy of motion Energy of matter Energy of space =+

Expansion of Space Hubble measured motions of galaxies All appear to move away from us Cosmic cooties? Expansion through space - WRONG Galaxies moving away from center No measurements show a center Copernican hypothesis underlies astronomy, and all science

Expansion of Space Expansion of space Galaxies at rest Space between galaxies expanding All galaxies see every other galaxy moving away No center Different kind of relative motion Observers at rest Reference frame in motion

Big Bang The Universe has expanded … from small to big from hot to cold from dense to rarified Standard framework of cosmology Only hypothesis that fits observations Scientific theory

Big Bang Observation Cosmic Microwave Background Remnant glow from hot early universe Seen in every direction on the sky\ Perfect thermal spectrum Time: half a million years after big bang Temperature: 3000 degrees Size: 1/1000 th 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

Cosmology

It’s Too Perfect Universe looks the same in all directions Cosmic Microwave Background Uniform across the entire sky to about one part in a hundred thousand Not enough time to achieve uniformity

Inflation Idea to create a smooth universe Hyper-expansion Regions previously in contact become widely separated Details Universe larger by factor of Occurs in of a second Universe degrees, supercools, reheats Knowledge of pre-inflation universe is lost

Inflation Physics Blame the particle physicists Energy is relative Cooling universe looks for energy minimum Briefly finds false energy minimum Energy of space drives inflation Release of energy from false minimum to true minimum provides reheating

Faster than Light Expansion? Inflation expands space much faster than the speed of light Doesn’t this violate relativity? No … Matter is not moving through space Space is growing, and carrying matter along for the ride Superluminal expansion is part of Big Bang

What’s the matter? Expansion – motion vs matter Measure motion Measure matter Too much motion or too little matter Dark Matter About 10 times more than ‘normal’ matter 90% of the matter is unobserved Conspiracy theory: Space and time controlled by unseen matter

Too Much Space Measure expansion rate of the universe Distant supernovae Amount of expansion between then and now Expansion is accelerating Cosmic concordance Other observations agree Age: 13.7 billion years Matter: 4.4% Dark Matter: 22% Dark Energy: 73%

The Fate of the Universe Dark Energy dominates universe Energy of space accelerates expansion Einstein’s “mistake” triumphs Universe expands ever faster Eventually faster than speed of light Objects disappear from observable universe Fabric of space-time stretched apart Energy of motion Energy of matter Energy of space =+

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

The Ultimate Free Lunch? Where does one get all this energy? Expansion  more space More space  more dark energy More dark energy  more expansion … What physics? Somewhat like inflation …

Cosmology Ultimately, one’s view of space and time doesn’t matter, because space and time are really in control

Nature of Space and Time Space can stretch, shrink, and warp Space expands, sometimes prodigiously Time can speed, slow down, or stop See the past, travel to the future Behavior depends on motion, matter, time, energy Not a background framework to the events of the universe, but a participant in those events