The Universe as a Time Machine

"Stars leave streaks of light in concentric circles in this Mar 16, 2012, view from the International Space Station"(Image & Caption Credit: NASA/Don Pettit)

What if the statement, "we can actually see the past“ was thrown at you and what if it is theoretically the truth? What if after all you don't need to build a whole time machine to go back in time and your eyes could do the job just fine? You see, when you look up at the starry sky, the dots of light you see in the sky are part of the past (in a way). Some of those stars may not exactly be there anymore as we look at them, but are still visible as the light has yet to reach Earth. It's a strange phenomenon to think about and so I wanted to explore time in space and the concept of seeing the past being in the reach of our hands. Is it truly as simple as said or does an opposition lurk?

What exactly is time?

I always find myself wondering if time exists or if it is just another scientific model. Well this is yet another question with answers that vary.  We can say time does not exist but rather a model formulated to accommodate our lives and to give a figure to “time” passing.  We say events occur at a certain date, hour, and second but  without these numerical values, all the phenomena in the Universe would still occur earlier or later. The SI unit for a second was not just randomly picked and has a long history of its own. From being measured as 1/86,400 of a mean solar day to being changed to a more accurate method as the solar days get longer from the gradual slowing of Earth's rotation. Later it was discovered that Cesium atoms (Cesium-133 isotope) can be made to vibrate very steadily and consistently.  This uncovering lead to a second to be considered the time taken for 9,192,631,770 of Cesium atom oscillations to occur.

Image of Cesium-133 composition (Credit: J. Wang/NIST)

Einstein's theoretical time machine 

On a random work day at the patent office a man decided to release some physics papers with theories, five to be specific. That man being Albert Einstein. One of the theories found in these papers included that time would slow down or dilate the closer it got to the speed of light while the mass would increase. This time dilation hypothesis has been tested by comparing times on four identical atomic clocks on commercial jet flights twice around the world, two flying eastward and two westwards. After comparing the times in a laboratory in the United States, it was found that the clocks carried had each lost a fraction of a second as per Einstein's hypothesis. Therefore based on Einstein's hypothesis if anything was to exceed the speed of light it would be moving backwards in time but as for current physics, nothing can exceed the speed of light.

Time in the movie Interstellar 

I can't possibly mention time and not mention Interstellar. Interstellar profoundly explores time in space, going from worm holes to time differences on the fictional Miller's planet and Earth. While sadly no matter how cool or scary it might be to have shortcuts in travelling from one point to another and potentially travelling faster than speed of light, worm holes are not proven. While they pose a hypothetical solution to some physics questions, there is not enough evidence to prove their existence and stability. What about the time difference on Miller's planet and Earth? The movie states that seven years on Earth is equal to just 1 hour on Miller's planet due to the strong gravitational force of the black hole (Gargantua) near it. This is actually a predicted event but of course in a wayyyy less dramatic way. With our current technology and the distances we can travel, astronauts would only feel a minuscule dilation.

Universes past through our eyes

When we go to astronomical distances, even light begins to struggle to appear as the flash we know it for, after all it also reaches a limit. Since most things are many light years away from Earth, it takes years for light photons to reach us. So when we look up at the sky we see stars and planets as they were years ago. Taking as an example, the closest astronomical object to the Earth: the Moon. Every time we look at the Moon we see it as it was one blink of an eye ago. This has caused me to wonder, no matter how illogical or how many physics laws it breaks, what if a planet at the right distance with life has technology capable of zooming into Earth. Would they see dinosaurs on Earth instead of humans or even no life at all? Instead, how far have humans from Earth been able to picture?

Hubble's furthest observation is of a galaxy GN-z11 observed as it was 13.4 billion years ago which places it within 400 million years of the Big Bang. This allows scientists to gain insight on the early stages of the universe we live in as the light we see is coming from 13.4 billion years ago. NASA uses observatories and high-powered space telescopes such as the Hubble as ”time machines” to help piece together the history of the universe we live in. Taking this logic we would only know what that galaxy's present state for us looks like 13.4 billion years into the future. 

 Image of galaxy GN-z11 (Credit: NASA)

Conclusion

While the concept of time travel is widely used in sci-fi movies and is undeniably fascinating, it is not fully fictional nor real but rather true in a way we do not usually imagine, similar to the concept of teleportation being reimagined with quantum teleportation. While we are theoretically looking in to the past every time we look up at the sky, the uncontrollably large life span of astronomical objects and the universe, compared to the average human life span make it near impossible that we will ever see a change in anything, such as a star becoming a supernova (but if we did we would see it as it had been occurring years back). It just comes down to the gamble of time.

Additional Sources: 50 Universe Ideas You Really Need to Know by Joanne Baker