Future

==In physics==
[[File:World line.svg|thumb|upright=1.2|A visualization of the future [[light cone]] (at the top), the present, and the past light cone in 2D space.]]

{{See also|Time in physics}}

In physics, time is the fourth dimension. Physicists argue that [[spacetime]] can be understood as a sort of stretchy fabric that bends due to forces such as gravity. In [[classical physics]] the future is just a half of the timeline, which is the same for all observers. In [[special relativity]] the flow of time is relative to the observer's [[frame of reference]]. The faster an observer is traveling away from a reference object, the slower that object seems to move through time. Hence, the future is not an objective notion anymore. A more modern notion is [[absolute future]], or the future [[light cone]]. While a person can move backward or forwards in the three spatial dimensions, many physicists argue you are only able to move forward in time.<ref name="autogenerated1">{{cite web|url=http://www.livescience.com/technology/070307_time_travel.html|title=You Can't Travel Back in Time, Scientists Say|website=[[Live Science]]|date=7 March 2007|access-date=31 December 2016}}</ref>

One of the outcomes of Special Relativity Theory is that a person can travel into the future (but never come back) by traveling at very high speeds. While this effect is negligible under ordinary conditions, space travel at very high speeds can change the flow of time considerably. As depicted in many [[science fiction]] stories and movies (e.g. ''[[Déjà Vu (2006 film)|Déjà Vu]]''), a person traveling for even a short time at near [[light speed]] will return to an Earth that is many years in the future.

Some physicists claim that by using a [[wormhole]] to connect two regions of spacetime a person could theoretically travel in time. Physicist [[Michio Kaku]] points out that to power this hypothetical time machine and "punch a hole into the fabric of space-time" would require the energy of a star. Another theory is that a person could travel in time with [[cosmic string]]s.