Here's a brief and simple explanation of something that is still expanding until today, the universe. I will be using the Big Bang theory as the cosmological blue print for this explanation. This theory has been widely accepted by scientists since the 1930's. It states that the universe started out from a very small, dense, and hot condition about 13.7 billion years ago. Think of it as a ball of energy ("a primeval atom" in Georges Lemaître's words) out to cause a great explosion that would set everything in motion. This caused everything to fly away from everything else with no center. One could only imagine what great destruction or beauty that might have been. As the point (primeval atom) got bigger, it caused space and time.
Studies and observations that scientists have made have confirmed the Big Bang model. Other models leave more questions than answers, like the idea of a fine tuned universe (who fine tunes it?).
To continue, there are various observations that support the Big Bang Theory. One of which is the amounts of chemical elements found in the universe. These are hydrogen, helium, and lithium.
Another important evidence is the red shift of very far away galaxies. The red shift is due to the Doppler effect, which is the change in the frequency of a wave that occurs when the source and observer are in motion relative to each other. The frequency increases when the source and observer approach each other and decreases when they move apart. Thus, an object moving towards the earth will look brighter compared to one moving away from it. Using this effect, scientists have measured the rate at which objects in space move and, as a result, have also estimated the age of the universe. According to their calculations, the age of the universe is 13.7 billion years old. This means that everything at that point in time was actually in the same place. The universe must have been extremely hot when it was in its early stage. This we know of because celestial bodies become colder as they expand.
Unfortunately, many people tend to incorporate the idea of the Big Bang Theory with their passed-down mystical nonsense. This is the case with cosmology, the study of the universe in its totality and humanity's place in it or, simply, the study of “all that is”. In the field of biology, Darwin's Theory of Evolution is also burdened with the same problem. Mystics and alike (religious fanatics for the most part) have misused these theories to support their claims when, in fact, they do the exact opposite of that: debunk them Oh, these nuts are a confused lot, all right, and they're out to drag along the misinformed and the gullible. Ambassadors of Intelligent Design, an assertion that the universe was caused by an intelligent designer, have maligned the credibility of the Big Bang Theory and the Theory of Evolution by paraphrasing them in support of their supernatural exploits. Religion, indeed, is pseudoscience at its finest.
The Big Bang model gives us a simple explanation that the universe began in an extremely small and hot space and has expanded henceforth. It gives measurements to show that the universe is still expanding today. The Big Bang Theory is scientific, meaning, that it stemmed from systematic research that involved experimentation and testing. Intelligent Design, on the other hand, is nothing like it. It is mystical. There is no way that it can be observed and tested as its claims goes beyond the senses.
Merging science with the supernatural smears the name of science and shrouds the truth from mankind. This is slander of no greater degree.