With Back to the Future celebrating time travel, we thought we should ask the question, does time travel really exist? Believe it or not, we are all traveling back in time, by the most minuscule amount. Despite lights superior speed, it is not infinitely fast which means that everything you see is actually how it was in the past.
We are living in the past
As intriguing as it sounds, really in everyday life this is totally irrelevant. So when you looking in the mirror, technically speaking you looking at yourself in the past, but then because of lights superior speed (only one thousand millionths of a second to travel 30 centimetres) the delay is invisible to us. However the further we get from an object the greater the delay becomes.
When you look up to our closest neighbour, the moon, you in fact seeing it a second in the paat. Yes interesting, but not that important. However when one looks the sun, you really are venturing back into the past.
Distance from the Sun
The Sun, 150 million kilometres away (93 million miles) which may appear close by cosmic standards, but when it comes to these distances the speed of light starts to feel pretty pedestrian. We are actually seeing the sun 8 minutes in the past. So for example if the Sun where some how to just be removed, we would have 8 minutes of sunshine left on our faces and to brighten the life around us. This delay also applies to gravity, as the speed of light is the fastest influence in the universe that anything can travel at. So only would we still see and feel the Sun if it were removed, but we would also continue to orbit around it. We are genuinely looking back in time every time we look at the Sun, meaning who really knows what is happening at this moment in time.
Other planets in the past
The Sun is only the start of our time traveling. As we look towards the planets and moons in our solar system, we continue to move further and further into the past. Light from Mars takes from four and twenty minutes to reach us, all depending on the relative positions of Earth and Mars in there orbits around the Sun. Again this doesn’t really effect us down here on earth, but it plays a vital role on the way we design and operate vehicles that are going to be driving on the surface of Mars.
When Mars is at its furthest point from us, to tell a Mars Rover it is about to crash or say fall off a cliff, would take a whole 40 minutes for us to be informed, and then another 40 minutes for us to inform it to stop. Therefore these vehicles are designed to tell themselves not to slip off a cliff, otherwise these process would be very slow. At its closest point, Jupiter is about thirty-two minutes away and as we get even further out into our solar system, light from the most distant, Neptune, takes around four hours to make the journey.
Fringes of the solar system
When you go to the very edge of our solar system, the round-trip travel time for radio signals sent and received by Voyager 1 on its journey into interstellar space is currently thirty-one hours, fifty-two minutes and twenty two seconds, as of September 2010.
Outside our solar system
As you start to look beyond our solar system and how long it takes for light to travel from the nearest neighbouring stars, we don’t bother with measurements in hours or days, but look at years. We see our closest star to the naked eye, Alpha Centauri, how it appeared four years in the past, and as these cosmic distances mount, our journey into the past becomes even deeper.
The Hubble Deep Field image captures light that was sent 13 billion years ago. This image is showing us something that happened just 600 million years after the bith of the Universe.