Eps Sci 3 Lecture 3. A Universe of Matter and Energy

**Everything in the universe is made of matter**

Mass (kg)

how much matter an object contains

Volume (m³)

how much space an object occupies

Density (kg/m³)

how tightly matter is packed

• help infer planet’s composition

  • high = rock and metal

  • low = gas/ice

Relationship between mass, volume, and density:

p = m/V

Mass vs weight

mass: amount of matter you have

weight: the gravitational force acting on that matter

W = mg

Organic molecules

contain carbon and usually hydrogen

• carbon can form many different stable chemical structures (including complex molecules essential for living organisms)

Phases of matter

• solid

• liquid

• gas

• plasma

How is temperature related to kinetic energy?

temperature reflects the average random KE of particles

Why do some substances require higher temp to melt?

1. temp influences particle motion

2. strength of chemical bonds affect how much energy is needed to disrupt a structure

Temperature alone doesn’t determine how matter behaves, bonding and molecular structure also matter

Celcius to kelvin conversion

K = C +273.15

Pressure

F/A

What does phase of water depend on?

temperature and pressure

How do we know the composition of the sun and the planets? why do objects look the way they do?

light

• provides info on distant objects that are too far away to routinely visit (or visit at all)

What does light reveal about a star’s properties

• chemical composition

• temperature

• motion

• physical conditions

Speed of light ( c)

3×10^8 m/s (300,000 km/s)

wavelength (λ)

distance between successive wave peaks

frequency (v)

number of wave peaks passing a point each second

speed in relation to wavelength and frequency

c = λv

• short wavelength = high frequency

• long wavelength = low frequency

Each photon carries an amount of energy determined by its frequency

E = hv = hc/λ

• h = planck’s constant: 6.63×10^-34 J*s

• shorter wavelength = higher frequency = higher proton energy

How can light behave as both a wave and particle?

→ double-slit experiment:

• imagine shining a light through 2 narrow slits

• observe pattern of alternating bright and dark regions

= wave-particle duality

Niels Bohr electron model

electrons could occupy only certain allowed energy levels: n = 1, n = 2, n = 3

• absorption: an e- absorbs energy and moves to a higher energy level

• emission: an e- drops to a lower energy and releases energy as a photon (∆E = hv)

Bohr Model

• Ground state = e- is in its lowest available energy state

• Excited state = e- has absorbed energy and moved to a higher state

• Ionized state = enough energy has been supplied to remove an e-

Electromagnetic spectrum

1. gamma

2. x-ray

3. uv

4. visible

5. infrared

6. microwave

7. radio

(increasing wavelength, decreasing photon energy and frequency)

How do objects produce light in the first place?

• fluorescence: matter absorbs energy and then emits light as it relaxes

• thermal emission: matter emits electromagnetic radiation because of its temp

• stimulated emission

f

fluorescence

matter absorbs energy and then emits light as it relaxes

thermal emission

matter emits electromagnetic radiation because of its temp

stimulated emission

an incoming photon triggers an excited system to emit another photon

more about thermal radiation

all objects with temperatures above absolute zero emit electromagnetic radiation, BUT don’t emit the same amount/wavelength distributino

Stefan-Boltzmann Law

F = σT^4

• Stefan-Boltzmann constant = 5.67×10^-8 W/(m²*K^4)

Wien’s Law

λmax = 3000 / T

How the Stefan-Boltzmann and Wien’s Laws work together

• Wien’s law: hotter = shorter peak wavelength

• Stefan-Boltzmann law: hotter = greater total energy emitted

What happened after the Big Bang

• in early universe, temps were extremely high BUT cooled down as it expanded

• matter existed as hot mixture of particles

• light could not travel freely

what happened after the universe cooled down

after 380,000 years, the temp decreased to around 3000K

• e- could combine with nuclei → nuclei atoms

• universe became transparent

• light could travel through space

Cosmic microwave background (CMB) radiation

= ancient radiation

as space expands, the wavelength of freely traveling photons are stretched = cosmological redshift: T(CMB) = 2.7 K

What did the evidence from Penzias and Wilson (1965) show?

persistent microwave signal = cosmic microwave background (powerful evidence that shows that the early universe was extremely hot and dense)

What does the CMB map show?

• colors indicate very small differences in temp'

  • red/orange: slightly warmer areas

  • blue: slightly cooler areas

• reflect differences in conditions of teh early universe (including density fluctuations)

CMB connection

early temp and density fluctuation → gravitational growth → galaxies → stars → planets → environments where life might emerge

Composition of the universe

ordinary matter = 5%

dark matter = 27%

dark energy = 68%

Evidence for dark matter

• galaxy rotation curves: materials in outer parts of galaxies often move much faster than expected from visible matter alone

• gravitational lensing: gravity bends path of light and when light from distant galaxy passes near massive object, its path can be deflected → distort or magnify the galaxy’s apparent image → estimate how much mass is present (including matter that cannot be seen)

Dark matter vs Dark energy — dark matter

• has gravitational effects that help explain galaxy dynamics and structure

• helps matter clump togehter

• about 27% of cosmic mass-energy

Dark matter vs dark energy — dark energy

• associated with accelerated cosmic expansion

• drives the observed acceleration of expansion

• about 68% of cosmic mass energy

The history of the universe

1. big bang and early expansino

2. first particles

3. first nuclei: light nuclei (such as hydrogen and helium) form

4. first atoms and freely traveling light: around 380,000 years later

5. first stars

6. galaxies and large-scale structure

7. accelerated expansion

8. present universe: approx 13.8 billion years after

what happens when light interacts with matter?

• reflection: light changes direction when it encounters a surface

• absorption: matter takes in light energy

• transmission: light passes through a material

→ light traveling through a planetary atmosphere can be absorbed at specific wavelengths, potentially revealing the gases present