From: mk_thisisit
Professor Brian Cox, a renowned physicist, discusses the nature of the universe, focusing on its expansion and the Big Bang theory [01:36:00]. He emphasizes the importance of understanding the origin and evolution of the cosmos [01:36:00].
Age and Scale of the Universe
The universe is estimated to be 13.8 billion years old [02:56:00]. Within the observable universe, there are approximately two trillion galaxies [03:01:00]. A fundamental question in cosmology is how this age is determined [03:15:00]. Measuring the age of something, even a stone, requires extensive nuclear physics research and specialized equipment [03:29:00]. Similarly, determining the age of the universe relies on complex measurements [03:50:00].
The Big Bang and Universal Expansion
Our universe is characterized by its expansion and cooling [07:03:00], a phenomenon discovered in the 1920s by American astronomer Edwin Hubble [17:39:00]. Hubble proved that distant galaxies are moving away from each other and from us [17:44:00]. This concept of space stretching or contracting was theoretically noted shortly after Einstein’s theory of gravity was published [17:20:00]. Measurements of this expansion and its rate of change over time allow scientists to calculate the age of the universe [17:51:00].
The universe’s age is defined as the time measured by a freely falling clock that began its measurement during the Big Bang [10:44:00]. The Big Bang describes the universe’s initial state as hot and dense [13:59:00]. Current theories, such as inflation, suggest that space and time existed before the universe entered this hot, dense “hot Big Bang” phase [14:07:00].
Light from Before the Big Bang
The oldest light observable in the universe is cosmic microwave radiation, which was emitted approximately 350 million years after the Big Bang [15:51:00]. Before this period, the universe was in a plasma state, too hot for atoms to form [16:09:00]. In this thick soup of hydrogen and helium nuclei and electrons, light could not pass through [16:30:00]. Therefore, light cannot be used to observe events from earlier than 350 million years after the Big Bang [16:37:00]. To look further back in time, other methods, such as studying neutrons or gravitational waves, would be necessary [16:57:00].
The Concept of Time and the Universe’s Beginning
Understanding the concept of time is crucial for comprehending the universe’s beginning [14:21:00]. In Einstein’s theory of relativity, space and time are woven together into spacetime, often called the “fabric of the universe” [09:53:00]. However, what time “really is” remains an active area of research [09:47:00].
The perceived asymmetry of time, where the future is ahead and the past has happened, is linked to the Big Bang being an extremely orderly, low-entropy phenomenon [11:56:00]. The second law of thermodynamics states that entropy always increases, meaning the future moves in the direction of increasing disorder [12:10:00]. This concept of time is known as thermodynamic time [12:23:00].
Modern research, particularly concerning black holes, suggests that space and time themselves may emerge from a deeper theory of quantum gravity that does not inherently include space and time [14:32:00]. Until the fundamental nature of space and time is understood, questions about the universe’s true beginning remain speculative [14:50:00].