Could some episodes from Doctor Who actually be possible
A good explanation of what time travel is is provided by the philosopher David Lewis. Lewis states that time travel is an experience that is different in duration when viewed from the external perspectives (in “external time”) or within (in “personal time”). Let’s say you have five minutes on your device, as recorded through (e.g.) your watch or your memories. After arriving, you realize that 150 years have passed since you left the world outside. It’s a great feeling to have traveled through time. A mere five seconds of time has covered more than 150 years of outside time.
As odd as it sounds, Einstein’s theories of Special Relativity introduced such possibilities to the field of physics in 1905. The theory states that the length of any process is determined by the speed of the person who is watching. The closer the relative velocity is to light speed, the longer the traveling process will take.
If you’d like to see the Earth one billion years from now and you’re worried that you’ve just 50 years of your life left. Special Relativity specifies that if you travel at that speed to the Earth, then your individual years may cover a billion Earth years.
In time travel that is backward, the time of personal and external travel differ in direction, and so journeys end in time outside prior to, not after, they begin. You have five personal minutes of travel 150 years in the past. General Relativity suggests that the universe is, in essence, curving time that could allow these divergences in personal and external time.
Relativity considers time and space as a single entitycalled “spacetime”. One of the most remarkable aspects that is unique to General Relativity is that it permits space and time axes to be interchanged, which means that the space axis of one observer can also be a time axis.
The year 1949 was the first time Austrian mathematics professor Kurt Godel utilized General Relativity to describe a universe in which adventurers are able to travel anywhere in (past or in the future) time, without traveling quicker than light. Godel’s universe is not bound in time or space, and everything in it revolves. However, our limited, non-rotating universe isn’t God’s. Be assured that you can spin an ultradense and very (maybe infinitively) long cylinder at a very high speed. Spacetime should be curving around the cylinder such that it is in the direction that the future’s local direction partially is a reflection of the past externally. These devices are referred to as ” Tipler Cylinders,” named after the scientist Frank Tipler.
Quantum theory suggests that “wormhole” connections between different spatial points are formed by chance and then break every day. There is a good chance that wormholes naturally formed are tiny and much smaller than an electron (and one billion trillion electrons could be squeezed into one teaspoon). However, you might be able to discover (or develop) the wormhole large enough and long-lasting enough to allow you to slide to the past. This isn’t easy, but it’s theoretically feasible.
It’s not possible to kill your Physics teacher.
Perhaps you can take a trip back to the past. What about paradoxes? What can you do to prevent from murdering your grandfather or yourself in your infant years? One solution is logic congruity.
Classical logic states that you can’t continuously kill an infant who reaches adulthood. However, Lewis says, time travel doesn’t have to mean doing what is logically impossible, provided that travelers’ actions in the past are in line with the time from which they originate. You could even try to kill your grandfather’s baby; however, something could stop you. You would cough, or your gun could be jammed. Lewisian time travel is (classically) constant, however it may appear a bit odd because seemingly plausible scenarios (like shooting an infant who is not protected) are not possible.
Another viewpoint is that time travel backwards calls for multiple worlds, that is, multiple different, but equally real versions of the physical world. Physics professor David Deutsch and philosopher Michael Lockwood believe that time travel should involve inter-world travel. If you are able to travel backwards through time, you will arrive in a world that is different from the one you grew up in and thus be free from your past once you arrive. It is possible to even kill different history’s equivalents to your grandfather and you.
Both of these ideas of time travel that is backwards may frustrate anyone looking to change their “one and only” past. Time travelers could either make history the way it is (Lewis) or make an entirely different historical record (Deutsch/Lockwood). But quantum logic may allow time travelers to alter the real (one-and-only) historical.