When talking about time travel, we must first understand there are different versions of time travel.
We can either travel forward or backward in time and can either view it or be able to participate in it. These options give us four types of time travel.
The four types of time travel:
Viewing the past
Participating in the past
Viewing the future
Participating in the future
Each of these versions has their own specific answer, so we will go over them separately. The concept of whether we return to our original time after the travel is irrelevant, as we'll discuss later on.
However, in order to understand whether time travel, in any of these forms, we must first understand the true concept of time and its relationship to space and matter.
The definition of time that I use in this article is simple:
"Time" is the passage of one moment to the next.
This definition begs, "What is a moment?".
A "moment" (for purposes of this article) is an instant defined by the position of all particles in relation to each other.
For example, one well-known moment was the precise split-second when the bullet hit John F. Kennedy's head. I will use this moment as a reference point when discussing traveling in the past.
With this in mind, let's work our way through the different types of time travel.
Viewing the past
This method is generally the one that most scientists talk about when they discuss time travel. When they talk about how time travel is possible, they usually talk about finding some way to travel faster than the speed of light. If a light beam is sent and afterward we activate time travel, we overtake the light and, in effect, see it sent off again from our new location. So when a "moment" occurs, we can head out beyond the light waves of that moment and see it again. Due to the immense distance required, this method is usually discussed in terms of traveling to solar systems far beyond our current capabilities.
In this method of time travel, we have no ability to interact with what happened. We can only observe. The most notable example of this type of time travel is stars. We see the light waves they sent off years ago, but have no way of interacting with the occurrences because they:
Are too far away
Have already happened
So with this in mind, we want to see JFK's murder. To do this we must travel faster than the light waves carrying those moments and view them.
OK, so Friday Nov. 22, 1963, 12:30:07 PM CMT is the time we are looking to witness. Around Elm Street Dallas Texas is the location.
In order to witness the event we must first calculate which direction that part of the Earth was facing so we know the best route to find the correct light waves. It does us no good to just zoom off past the speed of light. We would most likely head in the wrong direction. After all, the light waves from an event don't pass through the Earth and head out equally in all directions. Just as an astronaut on the other side of the moon could not get our attention with flares.
So we calculate the approximate location of the light waves. Now we must catch up to them.
Is faster than light speed possible? Not currently. It won't happen any time soon. Right now the most common theory as to how to do it involves bending space so you have a shorter travel distance than the light wave. However regardless of the theory and/or technique used faster than light travel still involves traveling through space faster than 186,000 miles per second. That's well out of our grasp so far. It will occur, but not yet.
But for the sake of argument let's pretend 100x light speed is currently possible. A ship takes off in the right direction, speeds out, overtakes the light rays and prepares its telescopes and recorders.
Now let's think about this for just a moment. Those light rays are going to be very far away. Well past the planet Pluto.
Let's take our best telescope (Hubble, if I'm not mistaken) and point it at Pluto. Let's pretend the telescope is 100x more powerful than it is right now. How much specific detail do you think we can see?
In a word, zero. Light dissipates as it travels just like any other wave. The details get blurrier the farther you go. This is simple physics.
We make devices to clear up and focus as best as we can, but the fact is we will never be able to make a device fast enough or clear enough to be able to zoom in on the famous assassination.
OK, so let's make things a little more reasonable. Let's pretend an attack occurred just 5 minutes ago and we can travel fast enough to see the event occur again 2 minutes from now. We can see what happened and head back to report the details missed the first time.
That is, as long as they occurred out in the open. No light waves could travel from an event, out the window and bank up toward our spacecraft for us to see and no passive "x-ray" types of technology exist. They all requir