26.5 The Expanding Universe
3 min read•june 12, 2024
The revolutionized our cosmic understanding. 's groundbreaking discovery, using the , revealed a correlation between galaxy distances and redshifts. This led to , now known as the , providing evidence for cosmic expansion.
Hubble's law helps calculate galaxy distances and defines the , representing the universe's expansion rate. Different models explain this expansion, from critical density to accelerating expansion. Variations in the arise from measurement techniques, errors, and local variations, shaping our evolving cosmic perspective.
Discovery and Implications of the Expanding Universe
Hubble's universe expansion discovery
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Top images from around the web for Hubble's universe expansion discovery
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- Used 100-inch Hooker telescope at observed distant galaxies
- Measured distances using as standard candles (consistent brightness allows distance calculation)
- Measured redshifts of galaxies by analyzing spectra
- is shift of spectral lines towards longer wavelengths due to (similar to pitch change of passing ambulance siren)
- Discovered correlation between distances to galaxies and redshifts
- More distant galaxies exhibited greater redshifts indicating faster recession velocities (, )
- Relationship known as Hubble's law provided evidence for expansion of universe
- This relationship is now referred to as the Hubble- law, acknowledging Georges Lemaître's earlier work
Application of Hubble's law
- Hubble's law states galaxy's proportional to distance
- , where is recession velocity, is distance, is Hubble constant
- Hubble constant represents current expansion rate of universe
- Value approximately 70 km/s/Mpc (kilometers per second per ) (3.26 million light-years)
- Calculating distance to galaxy using Hubble's law:
- Measure galaxy's from spectrum
- Convert redshift to recession velocity using Doppler shift formula
- Divide recession velocity by Hubble constant to obtain distance
- The observed redshift in this context is known as , distinct from other types of redshift
Models of expanding universe
- :
- Universe has just enough matter to eventually halt expansion
- Spatially flat and will expand forever but expansion rate will approach zero (like ball rolled uphill)
- :
- Universe has less than critical density of matter
- Spatially open (negatively curved) and will expand forever (like saddle shape)
- :
- Universe has more than critical density of matter
- Spatially closed (positively curved) and will eventually collapse in "" (like surface of sphere)
- :
- Supported by observations of distant supernovae suggesting accelerating expansion
- Attributed to , mysterious form of energy permeating space
- Implies universe will continue expanding at increasing rate leading to "" (like expanding balloon)
Variations in Hubble constant
- Different measurement techniques:
- Cepheid variable stars and as standard candles (consistent brightness)
- and (CMB) radiation (leftover heat from Big Bang)
- Systematic errors in distance measurements:
- Calibration uncertainties in (errors compound at large distances)
- Difficulties accurately determining distances to distant galaxies
- Local variations in expansion rate:
- Presence of large-scale structures like galaxy clusters can affect local measurements (gravitational attraction)
- Hubble constant may vary depending on direction and scale of observations
- Differences in assumed cosmological model:
- Choice of cosmological parameters such as matter density and can influence derived value of Hubble constant (assumptions built into calculations)
Fundamental concepts in cosmology
- : The universe is homogeneous and isotropic on large scales
- : Describe the expansion of space in homogeneous and isotropic models of the universe
- : A parameter that represents the relative expansion of the universe
- : A theory proposing that the early universe underwent a period of rapid exponential expansion
Key Terms to Review (42)
Accelerating Expansion Model: The accelerating expansion model, also known as the Lambda-CDM model, is the prevailing cosmological model that describes the expansion of the universe. It proposes that the universe is undergoing an accelerated expansion, driven by a mysterious dark energy that counteracts the gravitational attraction of matter.
Andromeda Galaxy: The Andromeda Galaxy, also known as Messier 31 or NGC 224, is a spiral galaxy located approximately 2.5 million light-years from Earth. It is the largest and most massive galaxy in the Local Group, which includes our own Milky Way Galaxy. The Andromeda Galaxy's vast size, distance, and relationship to the Milky Way make it a crucial object of study in understanding the large-scale structure and evolution of the universe.
Big crunch: The Big Crunch is a theoretical scenario in which the expansion of the universe eventually reverses, causing it to collapse back into a singularity. This hypothesis contrasts with the idea of an ever-expanding universe and suggests a cyclic model of cosmic evolution.
Big Crunch: The Big Crunch is a hypothetical scenario in which the current expansion of the universe reverses, leading to an eventual collapse of all matter back into an extremely hot and dense state, similar to the initial conditions of the Big Bang. This concept is closely tied to the overall model and evolution of the universe.
Big Freeze: The Big Freeze, also known as the 'Big Chill' or the 'Big Rip,' is a hypothetical scenario in cosmology where the continued expansion of the universe leads to a state of ever-decreasing temperatures, eventually resulting in the complete freezing of all matter in the universe. This term is closely related to the concept of the Expanding Universe, as the ongoing expansion is the driving force behind this eventual fate of the cosmos.
Cepheid Variable Stars: Cepheid variable stars are a type of pulsating variable star that exhibit a regular pattern of brightness changes over time. These stars are important in the study of galaxies and the expansion of the universe due to their unique properties.
Closed Model: A closed model, in the context of cosmology, refers to a model of the universe that is finite in size and closed in on itself, with the total mass and energy of the universe being finite and contained within a closed spatial geometry. This model suggests that the universe has a beginning and an end, and that its overall structure and evolution can be described by a specific set of physical laws and parameters.
Cosmic Distance Ladder: The cosmic distance ladder is a series of techniques used by astronomers to measure the distances to celestial objects, ranging from the nearest stars to the most distant galaxies. This step-by-step approach allows for the accurate determination of the scale of the universe.
Cosmic Inflation: Cosmic inflation is a theory that describes an extremely rapid exponential expansion of the universe in the first fraction of a second after the Big Bang. This rapid expansion is thought to have smoothed out irregularities and set the stage for the universe we observe today.
Cosmic Microwave Background: The cosmic microwave background (CMB) is the oldest light in the universe, a faint glow that permeates all of space and is a remnant of the early stages of the universe's formation. It provides crucial information about the origins and evolution of the universe, as well as its large-scale structure and composition.
Cosmological principle: The cosmological principle states that the universe is homogeneous and isotropic when viewed on a large enough scale. This means that the distribution of matter and energy is uniform, and the universe looks the same in all directions.
Cosmological Principle: The cosmological principle is a fundamental assumption in cosmology that states the universe is homogeneous and isotropic on large scales. This means that the properties of the universe are the same everywhere (homogeneous) and look the same in all directions (isotropic), regardless of one's location or orientation.
Cosmological Redshift: Cosmological redshift is the shift in the wavelength of light from distant galaxies or other celestial objects, caused by the expansion of the universe. This phenomenon is a crucial piece of evidence supporting the Big Bang theory and the concept of an expanding universe.
Critical Density Model: The critical density model is a cosmological model that describes the expansion of the universe based on the concept of a critical density. It suggests that the overall density of the universe determines the ultimate fate of its expansion, with the critical density acting as a threshold between a universe that will expand forever and one that will eventually collapse back on itself.
Dark energy: Dark energy is a mysterious form of energy that makes up about 68% of the universe and is responsible for its accelerated expansion. Its exact nature remains unknown, but it is a crucial component in cosmological models.
Dark Energy: Dark energy is a mysterious and pervasive form of energy that appears to be driving the accelerated expansion of the universe. It is a fundamental component of the universe that makes up approximately 68% of the total energy content of the cosmos.
The discovery of dark energy has revolutionized our understanding of the universe, as it challenges the traditional models of cosmology and the evolution of the universe. Dark energy is a crucial concept that helps explain the large-scale structure and dynamics of the universe, as well as its past, present, and future.
Doppler effect: The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer moving relative to the wave source. It is commonly observed in sound waves but also applies to light waves, making it crucial for astronomical observations.
Doppler Effect: The Doppler effect is the change in the observed frequency or wavelength of a wave (such as sound or light) due to the relative motion between the source and the observer. It is a fundamental concept in astronomy that has numerous applications across various topics.
Edwin Hubble: Edwin Hubble was an American astronomer who made groundbreaking contributions to our understanding of the universe. He is best known for his observations and discoveries that led to the realization that the universe is expanding, and that galaxies beyond our own Milky Way exist.
Expanding universe: The expanding universe is the concept that the universe has been growing continuously since the Big Bang. This expansion is evidenced by the observation that galaxies are moving away from each other.
Friedmann Equations: The Friedmann equations are a set of fundamental equations in cosmology that describe the expansion and evolution of the universe. They were derived by the Russian mathematician and physicist Alexander Friedmann in 1922, based on Einstein's theory of general relativity and the cosmological principle.
Gravitational Lensing: Gravitational lensing is the bending of light by the gravitational field of a massive object, such as a galaxy or a black hole. This phenomenon occurs because the presence of matter distorts the fabric of spacetime, causing light to follow a curved path as it travels through this warped spacetime.
Hooker Telescope: The Hooker Telescope is a historic reflecting telescope that played a significant role in the discovery of galaxies and the expansion of the universe. It was the largest telescope in the world from 1917 to 1948, and its powerful observations helped astronomers make groundbreaking discoveries about the nature of the cosmos.
Hubble: "Hubble" refers to the Hubble Space Telescope, a powerful observatory launched into low Earth orbit in 1990. It has provided invaluable data on celestial objects and phenomena, significantly advancing our understanding of the universe.
Hubble constant: The Hubble constant is the rate of expansion of the universe, measured in kilometers per second per megaparsec (km/s/Mpc). It provides a relationship between the distance of galaxies and their recessional velocity due to cosmic expansion.
Hubble Constant: The Hubble constant is a fundamental parameter in cosmology that describes the rate of expansion of the universe. It represents the relationship between the distance to a galaxy and its recessional velocity, providing a measure of the expansion rate of the observable universe.
Hubble-Lemaître law: The Hubble-Lemaître law is a fundamental principle in cosmology that describes the relationship between the recessional velocity of galaxies and their distance from the observer. It states that the recessional velocity of a galaxy is proportional to its distance from the observer, indicating that the universe is expanding.
Hubble’s law: Hubble's law states that the velocity at which a galaxy moves away from us is directly proportional to its distance from us. This relationship supports the concept of an expanding universe.
Hubble's Law: Hubble's Law is a fundamental principle in cosmology that describes the relationship between the distance of a galaxy from the Milky Way and its recessional velocity. It states that the farther a galaxy is from our own, the faster it is moving away from us, indicating an expanding universe.
Humason: Milton Humason was an American astronomer who played a crucial role in providing observational evidence for the expanding universe. Working with Edwin Hubble, he measured the redshifts of galaxies, establishing the relationship between redshift and distance.
Lemaître: Lemaître was a Belgian priest, astronomer, and physicist who proposed the idea of an expanding universe. He is widely credited with formulating what would later become known as the Big Bang Theory.
Megaparsec: A megaparsec (Mpc) is a fundamental unit of distance used in astronomy, equivalent to one million parsecs or approximately 3.26 million light-years. This unit is commonly employed when describing the vast scales of the Universe, particularly in the context of measuring distances to galaxies and other celestial objects beyond our Milky Way galaxy.
Mount Wilson Observatory: The Mount Wilson Observatory is a renowned astronomical observatory located on Mount Wilson in California. It has played a pivotal role in the discovery of galaxies and our understanding of the expanding universe, making it a crucial institution in the field of astronomy.
Open Model: An open model, in the context of cosmology, refers to a universe that has a density parameter (Ω) less than 1, indicating that the universe will eventually expand forever. This model contrasts with a closed universe, which has a density parameter greater than 1 and will eventually recollapse.
Recession Velocity: Recession velocity refers to the speed at which a galaxy is moving away from the Milky Way galaxy due to the expansion of the universe. It is a key concept in understanding the Expanding Universe, one of the fundamental theories of modern cosmology.
Redshift: Redshift is the phenomenon where the wavelength of light from an object increases, making it appear more red. It is often observed in light from galaxies moving away from us, indicating the expansion of the universe.
Redshift: Redshift is the phenomenon where the wavelength of light emitted from a distant object is shifted towards longer, or redder, wavelengths compared to the original wavelength. This shift in the observed wavelength is caused by the relative motion between the object and the observer, as well as the expansion of the universe.
Scale Factor: The scale factor is a numerical value that represents the ratio between the size of an object or image and its actual or original size. It is a fundamental concept in the study of the expanding universe, as it describes the relationship between the current size of the universe and its size at earlier stages of cosmic evolution.
Slipher: Vesto Melvin Slipher was an American astronomer known for his pioneering work on galaxy redshifts. His observations laid the foundation for the discovery of the expanding universe.
Triangulum Galaxy: The Triangulum Galaxy, also known as Messier 33 or NGC 598, is a spiral galaxy located in the constellation Triangulum. It is the third-largest member of the Local Group of galaxies, after the Andromeda Galaxy and the Milky Way.
Type Ia supernovae: A Type Ia supernova is a powerful and luminous stellar explosion resulting from the thermonuclear disruption of a white dwarf in a binary system. It occurs when the white dwarf accretes matter from its companion star, reaching the Chandrasekhar limit and igniting carbon fusion uncontrollably.
Type Ia Supernovae: Type Ia supernovae are a specific class of supernovae that occur when a white dwarf star in a binary system accretes enough material from its companion to exceed the Chandrasekhar limit, causing the white dwarf to undergo a thermonuclear explosion. These events are remarkably consistent in their intrinsic brightness, making them valuable standard candles for measuring extragalactic distances and studying the expansion of the universe.