Global challenges Study Guide

Energy is fundamental to human society, powering everything from homes and transport to industries and communication. The primary energy sources available on Earth can be broadly categorised into two main types: renewable and non-renewable. Non-renewable energy sources are those that are used up much faster than they are naturally formed, meaning their supply is limited and will eventually run out. Examples include fossil fuels (coal, oil, and natural gas) and nuclear fuel (uranium). These sources are typically used for large-scale electricity generation, heating, and transportation. Renewable energy sources, in contrast, are naturally replenished or regenerated over a relatively short timescale, making their supply virtually inexhaustible. Examples include solar, wind, hydroelectric, geothermal, tidal, and biomass energy. These sources are increasingly used for electricity generation, and sometimes for heating or direct mechanical work. The choice of energy source often depends on factors such as availability, cost, environmental impact, and specific application. Understanding the characteristics and uses of each type is crucial for addressing global energy demands and sustainability challenges.

The Big Bang theory is the prevailing cosmological model explaining the early development of the Universe. One of the strongest pieces of evidence supporting this theory is the observation of 'red shift' in the light from distant galaxies. When we observe light from galaxies far away, the spectral lines within that light are shifted towards the red end of the electromagnetic spectrum. This phenomenon, known as red shift, indicates that the source of the light is moving away from the observer. The greater the red shift, the faster the galaxy is moving away from us.

This universal recession of galaxies implies that the entire Universe is expanding. If the Universe is currently expanding, then by extrapolating backwards in time, it must have been smaller in the past. This backward extrapolation leads to a point where all matter and energy in the Universe were concentrated in an extremely hot and dense state, which is the cornerstone of the Big Bang theory. The expansion is not just galaxies moving through a static space; rather, it is the space itself that is expanding, carrying the galaxies along with it. This is analogous to points on the surface of an inflating balloon, where all points move away from each other without a central point of expansion. Therefore, the observed red shift provides compelling evidence for an expanding universe, which in turn supports the Big Bang model of the Universe's origin.