Space and Time Can Warp Your Mind

Frank SummersSpace Telescope Science InstituteJune 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 1015

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 variableMotion through time constantChange 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

Speed of Light

Finite186,000 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*365.25 1 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 observableProperties Spherical Centered on the observer Horizon, not edge

Special Theory of Relativity

Special Theory of Relativity

Speed of light is an absolute - cPhysics 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(0.1 + 0.95) c(1 + 0.1*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 distanceMeasure timeCalculate speed of light

Thought Experiment - motion

mirror

light

Measure distanceMeasure timeCalculate 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 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 dialation Time 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

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

General Theory of Relativity

Matter warps spaceRe-interpret gravity as geometry Straight paths, but in curved space Geodesic

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 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 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 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: 1/1000th 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

Cosmology

It’s Too Perfect

Universe looks the same in all directionsCosmic 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 1043

Occurs in 10-32 of a second Universe 1026 degrees, supercools,

reheats Knowledge of pre-inflation universe is lost

Inflation Physics

Blame the particle physicistsEnergy is relativeCooling universe looks for energy minimumBriefly finds false energy minimumEnergy of space drives inflationRelease 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 apartEnergy

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 warpSpace expands, sometimes prodigiouslyTime can speed, slow down, or stopSee the past, travel to the futureBehavior depends on motion, matter, time, energy

Not a background framework to the events of the universe, but a participant

in those events