The current state of the environment is referred to as the Present. The current state includes the position, velocities, and all other attributes that fully describe the current environment.
The environment evolves to the next state. For example suppose a sheet of paper is currently on a desk and falls to the floor, then the next state of the environment is identical to the current state except for the new location of the paper. This evolution of the environment is what we think of as time.
The Past is the progression of states that have evolved to the current state. Evidence of these past states is imprinted in the current state. This imprinted evidence of past states provides the knowledge that we have of the past.
Some examples of this imprinted evidence include:
- our memories
- photographs, paintings, written records
- data stored on the internet
The Future refers to the states that the current state will evolve to. The current state contains imprinted information which allows the future to be predicted.
For example weather forecasting is accomplished by utilizing information from the current state (including pressure & temperature measurements, satellite data, and computer algorithms), and storing the weather prediction in the next state. This prediction is kept in a safe place so it continues to be readily available in subsequent states. Finally, after evolving through many states, the prediction is checked by comparing it against the state for which the prediction was made.
Speed of Time
The rate at which states evolve is dependent on the environment. For example, the rate which food spoils is slower in colder environments. Einstein's Special Relativity Theory provides a better example, in which the rate states evolve is slower for objects which are moving at a large velocity; this is known as Time Dilation.
Time Travel to the Future
Recall that the future refers to states that will be evolved to. So, by definition, everything is traveling through time into the future. However, when we think of time travel to the future, we are expecting to be transported to the distant future. Travel to the distant future can be achieved by taking advantage of Time Dilation, that is by moving at a velocity near the speed of light to slow the rate of evolution of states for the person or object that is moving.
Time Travel to the Past
Time travel to the past may be possible, but not in the way that most people think of time travel to the past.
To travel to the past we first need to have an accurate imprint of the past saved in the current state. Next find an available location in the present and make an accurate rendition from this saved imprint of the past.
There are a couple of problems with this approach:
- making an identical copy of a past environment is probably impossible, a nearly identical copy would have to suffice
- this copy of the past is embedded in a different surrounding environment than it originally was.
Entropy is a measure of the amount of disorder in a system. Higher entropy means more disorder. The entropy of a closed system increases over time. A closed system is a system in which there are no external interactions.
Consider a quantity of blocks neatly arranged on a table (in a low entropy state), there is a barrier around the edge of the table so the blocks can't fall off. Now shake the table to create the next state, the blocks will have moved to a more disordered (higher entropy) state. Shake the table again, the blocks will move to yet an even higher entropy state.
Entropy can decrease in several ways.
- The most common way entropy is decreased is by application of Energy. In the above example, someone could push the blocks back into their original low entropy configuration.
- The second way entropy may decrease is through random chance. For example, shaking the table a third time could result in all of the blocks moving back to their original ordered position. Of course this is very unlikely.
- Finally, when a system has reached it's highest entropy, then the entropy of subsequent states will fluctuate between slightly lower and slightly higher entropy. This is the case after the table has been shaken many times to achieve the highest entropy.
Time and Entropy in the Universe
The Universe began in a state of very low entropy. The universe was very small at the beginning. A chronology of the universe assigns time equal 0 to this initial state. The current state of the universe contains imprinted evidence which supports this theory, such as the cosmic microwave background radiation, and the red shifted light arriving from distant galaxies.
There are many theories for what the universe will look like in the distant future. Currently, the most accepted theory is that the universe will expand at an ever increasing rate, black holes will evaporate, protons will decay, and the universe will become increasingly large, dark, and empty,
I have concerns about both the beginning and end of the universe, that is described above.
Regarding the beginning, I believe that states must have existed that evolved into what we currently call the initial state of the universe. If this is correct, then the entropy of the initial state would probably not have been exactly zero; and evidence for what evolved into the initial state may still be available.
Regarding the distant future, I believe there is more to the future than an increasingly large, dark, and empty universe. Recall the blocks on the shaking table reached a maximum entropy because they were confined to the table by a barrier around the edge of the table. Shake the table long enough and the barrier will fall apart, allowing the blocks to fall to the floor (higher entropy). I believe something similar is in store for the distant future of the universe, where as yet unknown avenues for entropy increase will occur.
Some of the mysteries of cosmology that will help us better understand the beginning and future of the universe are:
Scientists have speculated about baby universes, and the multiverse. Some have claimed to have observed evidence of the existence of other universes in the cosmic background radiation. If these speculations are correct then the interactions between universes will need to be included in theories of our universe. This could change our current theories of the beginning and future of the universe.
Astronomers have found that the universe is expanding at an increasing rate. This expansion is not consistent with the expansion that we expect if the force of gravity is the only factor. The term Dark Energy is used to describe this mystery repulsive force which is causing space to expand. The increase in volume of the universe seems to provide more possible states for the matter and energy that make up the universe; providing the possibility of higher entropy. It is also possible that space itself has entropy.