ELECTRONS CAN BE ENERGIZED 2 1 3 What

ELECTRONS CAN BE ENERGIZED 2 1 3 What happens when they are excited?

ENERGIZED E - EMIT LIGHT Energy absorbed e- is energized, moves to a more distant (higher) orbit Ground state e. Light nrg emitted Can’t sustain higher energy level, falls back to ground state V 1

2. Absorb energy and jump to excited state 3. Electrons in an elevated orbit/shell; higher energy but unstable E energize! 1. Ground State electrons in expected orbit; stable, low energy 4. Fall back and release energy as light! V 2

Λ’S VISIBLE VIA FLAME COLOR, SET OF SPECTRAL LINES • Emitted wavelengths include different colors of visible light • Combined wavelengths are visible in a flame test • Split the light using a spectroscope to see the individual wavelengths Mercury

ENERGIZED E - PRODUCE UNIQUE Λ’S ground state The • • • wave frequency emitted depends on the atom the electron its ground state how much energy it absorbed how far ‘back’ it falls.

Example: Hydrogen, with its single e. Produces this set of spectral lines

MORE ENERGY ABSORBED = FURTHER MOVEMENT FROM GROUND STATE THIS HIGHER ENERGY REFLECTED IN HIGHER FREQUENCY OF LIGHT EMITTED High energy Low energy transitions Line spectra; energized electrons

SPECTRA PATTERN IS AN ELEMENTS ATOMIC FINGERPRINT �Again reflects: § unique atom § unique electron set § e - ground state § energy absorbed § how far ‘back’ e falls He Hg Ne Wavelengths separated by a prism or diffraction grating

IDENTIFY THESE ELEMENTS! Hg H Ne He

ONCE KNOWN, SPECTRA ARE COMPARED TO STARS AND GALAXIES star HD 21619 Absorption spectra photograph Line profile digital light level graph: intensity v wavelength

Problem… Stars, galaxies spectral lines are out of place Ex: wavelengths longer than expected, or red-shifted

EXPLANATION: DOPPLER EFFECT The wavelengths only appear to change In fact, the emitting source is moving, relative to us Waves take longer to reach us, therefore seem ‘stretched’ Red-shift Moving towards you ‘shortens’ the waves Credit Edwin Hubble, 1929

The Doppler Effect is the perceived change in wave length and frequency due to the motion of the source or observer Change in sound wave frequency changes the pitch Interactive another

Sonar = sound waves radar = radio waves Bens echolocation episodes 1 & 2

When the wave is light, the frequency shift and wavelength change reflect a shift along the EM spectrum

THE DEGREE OF SHIFT VARIES What does this mean? Less shift More shift

V: D Measuring the red-shift allows us to determine distance, direction of motion, and velocity of a distant-sky object

HUBBLE’S CONCLUSIONS � Distant galaxies have a redshifted spectrum Galaxies are moving away from us* �The more distant the galaxy, the more red-shifted The universe is expanding �Velocity proportional to distance; Hubble’s Law The more distant galaxies are moving away faster**

*ARISTOTLE VINDICATED? So we ARE the center of the universe! Nope, sorry

**FASTER AND FASTER? �Gravity should slow the expansion § In fact, the expansion rate today is greater than in the past �What is ‘pushing’ the galaxies apart? § A misunderstanding of gravity? Dark energy? Dark matter? �What does this mean for the universe? § Cold, dark, empty “Einstein said we could never understand it all”

SO WHAT? � Can reasonably infer the universe was smaller earlier in time And smaller earlier than that, and … � Until the time when all matter, energy, light, space was contained in a single point: the Singularity �The expansion of the singularity is the Big Bang origin of the universe Minute physics (5) Annenberg (27)

MORE EVIDENCE Cosmic Microwave Background Radiation (CMBR) First & oldest, light in the universe 300, 000 yrs post-Big Bang (13. 7 bya) The most distant, most red-shifted light in the universe – microwave lengths TED: Sound of the Universe