Research Question 2

Research Question 2research Question

Why do astronomers believe that the world is continuously expanding? How did they come to this conclusion? Explanation When scientist talk of expanding Universe, they mean that since the beginning of the Universe with the Big Bang, it has been growing ever since. In other words, galaxies found outside the world tend to move away from us, while the galaxies farthest away are moving the fastest. Based on the scientist's reasoning, then regardless of the galaxy that one might be in, the rest of the galaxies are moving away from you. According to Conlon et al. (2017), galaxies move in space and not through space. The Universe lacks a centre, and everything tends to move away from everything else found in the Universe. The first idea about the expanding Universe was formulated by Edwin Hubble in 1925.in his work, "He proved that there is a direct relationship between the speeds of distant galaxies and their distances from Earth." The concept was later named the Hubble's Law. Hubble telescope used in making observations was also named after him. Hubble constant which is the "the single number that describes the rate of the cosmic expansion, relating the apparent recession velocities of external galaxies to their distance" ("What does it mean when they say the universe is expanding?", 2020) was equally named after him.

Paper For Above instruction

The evidence supporting the idea that the universe is continuously expanding is rooted in observational astronomy, primarily through the work of Edwin Hubble and subsequent cosmological research. Hubble's observations in the early 20th century revolutionized our understanding of the cosmos. By analyzing the spectra of distant galaxies, Hubble identified a relationship—now known as Hubble's Law—demonstrating that the velocity at which galaxies recede from us correlates directly with their distance. This observation provided strong evidence that the universe is not static but expanding uniformly in all directions.

Hubble’s Law posits that the velocity of a galaxy moving away from us is proportional to its distance from Earth. Mathematically, this relationship is expressed as v = H₀ × d, where v is the recessional velocity, d is the distance, and H₀ is the Hubble Constant. This discovery implied that the universe was once concentrated in a single point—a groundbreaking realization that led to the Big Bang theory. The expansion of the universe was further confirmed by the discovery of redshift phenomena in the spectra of galaxies. Redshift occurs because the wavelength of light stretches as galaxies move away, shifting the light towards the red part of the spectrum (Hubble, 1929).

Moreover, modern cosmology has supported this model through observations of the Cosmic Microwave Background (CMB) radiation, which is considered the afterglow of the Big Bang. Measurements of the CMB by satellites such as COBE, WMAP, and Planck show a universe that originated from a hot, dense state and has been expanding ever since. Additionally, Type Ia supernovae observations have revealed that the expansion of the universe is accelerating, leading to the introduction of dark energy into cosmological models (Riess et al., 1998; Perlmutter et al., 1999). These findings refine our understanding of the universe's expansion rate and its dynamical evolution.

The conceptual shift from a static to an expanding universe was deeply influenced by Einstein's theory of General Relativity, which provided the framework for modern cosmological models. Einstein initially introduced the cosmological constant to maintain a static universe but later acknowledged that his equations predicted an expanding cosmos. The development of the Friedmann-Lemaître-Robertson-Walker (FLRW) models formalized the mathematics of an expanding universe compatible with observations (Friedmann, 1922; Lemaître, 1927).

In essence, the convergence of observational evidence—redshifts, the cosmic microwave background, and supernova data—alongside the theoretical framework of general relativity, form the core reasons why astronomers believe the universe is continuously expanding. This understanding underpins much of modern cosmology and leads to ongoing inquiries into the nature of cosmic acceleration, dark energy, and the ultimate fate of the universe.

References

• Conlon, M., Coble, K., Bailey, J. M., & Cominsky, L. R. (2017). Investigating undergraduate students' ideas about the fate of the Universe. Physical Review Physics Education Research, 13(2), 020128.
• Hubble, E. (1929). A relation between distance and radial velocity among extra-galactic nebulae. Proceedings of the National Academy of Sciences, 15(3), 168–173.
• Perlmutter, S., Aldering, G., Goldhaber, G., et al. (1999). Measurements of Ω and Λ from 42 high-redshift supernovae. The Astrophysical Journal, 517(2), 565–586.
• Riess, A. G., Filippenko, A. V., Challis, P., et al. (1998). Observational evidence from supernovae for an accelerating universe and a cosmological constant. The Astronomical Journal, 116(3), 1009–1038.
• Friedmann, A. (1922). On the curvature of the universe. Zeitschrift für Physik, 10(1), 377–386.
• Lemaître, G. (1927). A homogeneous universe of constant mass and increasing radius accounting for the radial velocity of extra-galactic nebulae. Monthly Notices of the Royal Astronomical Society, 91, 483–490.
• Penoyre, Z., Belokurov, V., Wyn Evans, N., Everall, A., & Koposov, S. E. (2020). Binary deviations from single object astrometry. Monthly Notices of the Royal Astronomical Society, 495(1), 324–333.
• Deller, A. T., Goss, W. M., Brisken, W. F., et al. (2019). Microarcsecond VLBI pulsar astrometry with PSRπ II. Parallax distances for 57 pulsars. The Astrophysical Journal, 875(2), 100.
• “What does it mean when they say the universe is expanding?” (2020). Retrieved from [URL]