Relativity (Lecture 8) Eps Sci

gravity assist

• take advantage of gravity and the path of another planet around the sun to change heliocentric velocity

Speed of Light

• universal speed limit

• c = 3 × 10^8 m/s

Special Theory of Relativity (measurements)

• Measurements of time/space/motion only make sense when we specify what they are measured relative to

• Motion is relative

Frame of Reference

Place from which motion is measured

Postulates

• the laws of nature are the same for everyone

• the speed of light in free space is the same for everyone

thought experiment

hypothetical situation in which a hypothesis or principle is described and examined logically for the purpose of thinking about its consequences

time dilation

• moving clocks run slow

Lorentz Factor

• how much does time dilate if you observe a moving clock

  • proper time/relative time

length contraction

• space changes when objects move through spacetime

  • - moving sticks appear shorter

general theory of relatively (gravity/spacetime)

• gravity is a manifestation of the curvature of spacetime

• spacetime is a four dimentional space

Tests of General Relativity

• perihelion precession of mercury’s orbit

• deflection of light by the sun

• gravitational redshift of light

Shapiro Delay

• signal near massive body is delayed

gravitational waves

• generated by relative motion of gravitating masses

  • equivalent to electromagnetic waves

binary pulsar

the orbit decays as a function of time

• amount of orbital energy that is lost matches the gravitational relativity prediction

gravitational lensing

• any massive object can bend light

  • matter that bends light from a distant source (aka Einstein Ring)

Wormholes

• tunnels through space time

  • unstable, extreme levels of energy required

tides

result of gravitational forces that distort the shape of an object (sun/moon exert ___ on Earth)

• solar are ½ as strong as lunar

• particularly strong at new/full moon

strength of tides

depends on M/d³

• M = mass of tide raising vody

• d = distance between bodies

Tidal effects

• tidal friction slows earth’s spin

• moon recedes from earth

fallacy of insufficiency

insufficient evidence is provided in support of a claim

peer review

evaluation of work by one or more people with similar competencies as the producers of the work

Unidentified Flying Objects

Rebranded : unidentified aerial phenomena

• most are natural phenomena

astrobiology

• hypothesis about alien life is tested

conspiracy theories

• explanation that relies on the existence of a consipracy when other explanations are more probable

cognitive bias

tendency to thinkin certain ways that can lead to deviations form a standard of rationality/good judgement

• anchoring — rely too heavily on one trait when making decisions

• availability — overestimate the likelihood of events with availability in memory

• confirmation — focus on what confirms preconceptions

• egocentric — tendency to rely to heavily on one’s own perspective

fallacy

use of invalid or otherwise faulty reasoning in an argument

ad hominem

• theory is discarded because of the person who argues it, not because of the content

affirming the consequent

if p, then q — q does not imply p

begging the question (petito principii)

when arguing for something, the claim itself is already assumed in the premise

denying the antecedent

if P, Q — not P does not imply not Q

false dilemma

presenting limited set of alternatives when there are others worth considering in the context

red herring

within an argument soem irrelevant issue is raised that diverts attention

illusion of causality

aka post hoc ergo propter hoc fallacy

• about to give vaccine → seizure

• if gave vaccine earlier, would have thought vaccine → seizure (thought it is the cause)

critical thinking

ability to think clearly and rationally about what to do or what to believe

delusion

• holding on to incorrect beliefs despite conflicting evidence