A few weeks ago, a friend asked me about the human voice and how far it could potentially travel without technological aid. There are many ways to interpret this question, and for each of those interpretations there are multiple answers. I gave the first answer that came into my head – it never stops. I realized immediately that the way I had answered was an answer to a different interpretation of the question than had been intended, but I thought it was fun, so I continued to explain.
When you speak, you set the molecules in the air around you in motion. Similar to waves in the ocean, each molecule affects the molecules around them, and these create a wave of sound that propagates forward through the air until it eventually seems to meet some kind of quiet end. Perhaps these waves are absorbed by the walls and furniture in the room. If you are outdoors, then maybe the wind can come along and disrupt the wave. The sound waves from other sources in the environment may come along and interfere with the ones you produced.
It’s kind of like throwing stones in a lake. If you throw just one stone, you can clearly see the ripples as they move outwards from where the stone dropped. If you then throw in other stones though, it soon becomes much more difficult to tell which ripples were caused by that first stone. If no additional stones are added, then the ripples will reach the edge of the water and possibly be reflected off in a new direction, but with ever decreasing energy. Eventually, all sign that a stone has been dropped seems to disappear. Your voice traveling through the air is very similar to dropping a stone in the water.
Of course, the whole process is much more complicated than that, but the details are not important for what I’m trying to explain. Whether it be waves in the water or waves in the air, it’s basically the same idea. There appears to be an end to the wave at some point, but this is not actually the case. The energy involved is gradually changed from one form into another until it is no longer recognizable as human speech, but it never actually disappears.
There are many possibilities that occur to me when I think about the fate of a sound wave. The energy in that wave may continue to bounce around for quite a while if it passes certain thresholds, but I’ll save the topic of thresholds for another blog. The energy may get transformed into heat energy, and the temperature of the environment may rise slightly, though you would never notice it. That heat energy may cause even more and smaller effects.
The point I’m trying to make is that through cause and effect, there is no end to the chain of events caused by any physical motion. The effect of any cause becomes the cause for the next effect and so on forever. At first macroscopic and few in number, the effects quickly become impossible to detect and quite possibly infinite in number over the course of time. Taken together though, at least where thresholds are involved, these countless effects may still be seen in the environment.
To me, this is a fascinating idea that I would like to talk about more in the future. I may not have explained it well here, but I’ll try again and again until I figure out how to explain it well. Everything you have ever said in your life is still out there somewhere, and possibly everywhere on Earth by now. Perhaps no human could ever gather your sayings back together again, but the universe keeps a record of them all. A record of every word you have ever spoken is kept in the walls and furniture of your home. It’s in the rocks and dirt outdoors, and in all of nature. It’s in the air around you and spreading out across the whole earth. It’s even making it’s way out into space, but I’ll discuss that at another time.