The expansion of space-time is a concept rooted in the theory of general relativity, which describes how matter and energy influence the fabric of space and time. According to the prevailing model of the universe, known as the Big Bang theory, space-time has been expanding since the early moments of the universe's existence.
Scientists have observed several phenomena that indicate the expansion of space-time:
Redshift of light: When light from distant galaxies or celestial objects reaches us, the wavelength of that light is stretched due to the expansion of space. This results in a phenomenon called redshift, where the light appears more shifted towards the red end of the electromagnetic spectrum. The degree of redshift corresponds to the distance and velocity of the objects, providing evidence for the expansion of space.
Hubble's Law: The American astronomer Edwin Hubble discovered a relationship between the distance of galaxies and their recessional velocities. This observation, known as Hubble's Law, demonstrates that galaxies are moving away from each other in an expanding universe.
Cosmic Microwave Background (CMB) radiation: The CMB is a faint radiation that permeates the entire universe, originating from a time shortly after the Big Bang. The uniformity and properties of the CMB provide further evidence for the expansion of space-time.
Large-scale structure of the universe: Observations of the distribution of galaxies on large scales reveal a pattern of clusters and voids, indicating the large-scale expansion and structure of the universe.
Gravitational waves: Gravitational waves are ripples in space-time caused by the acceleration of massive objects. The detection of gravitational waves from merging black holes or neutron stars indirectly supports the concept of an expanding universe.
These observations collectively provide strong evidence for the expansion of space-time. It is important to note that this expansion refers to the stretching of space itself, rather than objects moving through space. The exact nature and dynamics of this expansion are still active areas of research in cosmology.