Chapter 1: Scientific Theory and the Big Bang — Vocabulary Flashcards

Vocabulary flashcards covering key terms and concepts from Chapter 1: Scientific Theory and the Big Bang.

Scientific theory

A well-supported explanation of a set of observations, based on evidence from repeated testing; explains the 'why' of phenomena and is the best current explanation, though not guaranteed to be true.

Hypothesis

An educated guess based on observation; can be supported or rejected by experimentation or further observation and cannot be proven true.

Law (scientific law)

A concise statement that predicts how a phenomenon will occur; describes what happens but does not explain why.

Observation

Careful noting of phenomena used to test a hypothesis; a fundamental step in the scientific method.

Big Bang Theory

The theory that explains the origin of the Universe as a beginning from a singularity with a rapid expansion that created space and time.

Singularity

A point in space-time where gravitational forces are so extreme that known laws of physics break down.

Gigantic expansion

The rapid early expansion of the Universe from the Big Bang, during which space and time were created.

Hubble’s Law

v = H0 d; the speed of a galaxy is proportional to its distance from Earth, indicating the Universe is expanding.

Redshift

The apparent lengthening of wavelengths (toward the red end of the spectrum) as objects move away from the observer.

Blue shift

The shortening of wavelengths (toward the blue end of the spectrum) as objects move toward the observer.

Doppler shift (Doppler effect)

Change in observed wavelength or frequency due to relative motion between source and observer.

Cosmic Microwave Background (CMB)

Remnant radiation from the early hot Universe, detected from all directions with nearly uniform intensity.

CMB temperature

The current average temperature of the cosmic microwave background, about 2.726 kelvin.

Abundance of light elements

Primordial proportions of hydrogen (~75%), helium (~25%), and trace lithium, explained by Big Bang nucleosynthesis.

Shape of the Universe

Possible geometries: closed (positive curvature), open (negative curvature), flat (zero curvature).

Closed Universe

Finite with positive curvature; may eventually recollapse in a Big Crunch.

Open Universe

Infinite with negative curvature; expands forever; parallel lines diverge.

Flat Universe

Infinite with zero curvature; parallel lines stay parallel; expansion slows but continues.

Density parameter (Omega0)

Critical density ratio determining curvature: Omega0

Dark matter

Matter that does not emit light but exerts gravity; inferred from gravitational effects; a significant portion of the Universe’s matter.

Dark energy

Mysterious energy driving the accelerated expansion of the Universe; makes up about 70% of the Universe.

Age of the Universe

Estimated age ranging from about 11.5 to 17.5 billion years; modern estimates around 13.8 billion years.

Radioactivity

Decay of radioactive isotopes; used to date rocks and estimate the ages of stars and the Universe.

White dwarfs

Old stellar remnants used to constrain the age of the Universe; dating yields roughly 12–13 billion years.

Hubble Space Telescope

NASA/ESA space telescope launched in 1990; provided many key astronomical observations.

Edwin Hubble

Astronomer who demonstrated the existence of other galaxies and that the Universe is expanding.

What Banged? (Neil Turok cyclic model)

Idea that the Big Bang may be one event in a cycle of repeated expansions and contractions of the Universe.

Big Bang vs explosion

The Big Bang did not occur in preexisting space; it created space and time themselves, akin to space expanding like a balloon.

Three Pillars of Proof

Three main observational evidences for the Big Bang: galaxy recession (Hubble’s Law), cosmic microwave background, and the abundance of light elements.