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At the speed of light



Abstract depiction of light traveling

The study of light, in physics, is called optics. Optics deals with the properties of light, how it interacts with other objects, and how it can be used. Personally, I find speed to be light's most intriguing property.


In 1676, Ole Christensen Rømer was the first to measure the speed of light using an astronomical unit called a light year. Throughout the years other scientists measured light's speed using various methods, and now we have a standard measure of 299,792,458 m/s; this means that light can circle the Earth 7.5 times in just one second!


Given the vast distance between celestial bodies and Earth, light has been used as a tool for measuring distance in space. A light year is how far light travels in one year. That is approximately 6 trillion miles. For perspective, the distance between Earth and the sun is 91.7 million miles.


Two questions raise from this:

a) Can humans travel at the speed of light?

b) Is time travel possible?


Can humans travel at the speed of light?

The simple answer to that question is NO.

Light is fast because it is made out of massless particles called photons. Almost everything else in the Universe has mass (which is different from weight). Following the theory of relativistic mass, the observed mass increases as speed increases. The speed of cars, trains, or airplanes have no significant impact on the mass; however when moving closer to the speed of light, the observed mass approaches infinite. When the mass is infinite, then Einstein's E=mc2 says that E (energy) is also infinite. That is the energy required to keep the object moving at c (the speed of light). To this day, that is impossible. Nonetheless, scientists continue looking for "loopholes" in the theory that could help us understand how it might be possible to travel at nearly the speed of light.


Is time travel possible?

The answer to this question is complicated as it is still an unsolved equation. The scientific opinion appears to be that time-travel wouldn't be like how it is seen in the movies where people are teleported to a different time; furthermore, current theories suggest that traveling to the past is impossible. While it may be out of our hands to travel into the past, traveling to the future is technically achievable.


While the speed of light doesn't really determine the answer to the question, I personally believe in these two points of view:

1.- When we look into space, we are observing light that has been traveling in space for years. The images we receive from far away galaxies show us how things that occurred were hundreds or even millions of years ago, thus we are effectively observing past events.

PHOTOGRAPH BY NASA, JPL, & HUBBLE HERITAGE TEAM STSCI, AURA
Photo by NASA and collaborators.

JADES-GS-z13-0 is one of the farthest galaxies known, located 33 billion light-years away and estimated to have formed just a few hundred million years after the Big Bang. Studying this galaxy is like looking through a window into a past event that could explain our present without us having to physically "travel" to the past to see it. Isn't that cool?


2. On the other hand, travel to the future is theoretically possible by speeding up the passage of time as experienced by someone traveling in space. This phenomena is presented in the movie Interstellar. A person could be at the edge of a black hole for a few hours and come back to find out then it has actually been multiple years! This is because more massive objects with great gravitational forces exert time dilation on individuals near it. This person can effectively "travel into the future", but unfortunately can not travel back.


Scientists are still working hard to find a solution to this problem with a unified theory that connects special relativity with modern day quantum mechanics.


If you are interested in diving deeper into these topics, I recommend you check out “A Brief History of Time,” by Stephen Hawking. His book goes in depth about the topics of famous astronomers, relativity, dark matter, black holes, and a lot of astrophysics.



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