May 16, 20195 min read

Where are you?

Updated: Jan 24, 2020

A photo-shopped image of a man walking in a place which resembles a fantastic night sky — Caught between worlds

It sounds like a stupid question, doesn’t it? But, seriously, how do you answer that question? Maybe a rational answer to it might be—in front of a laptop or a cellphone. Sure enough, you are constrained within a set of coordinates, wherever you are. But, if you are in a car, your coordinates are constantly changing, meaning you never belong to a set of coordinates for more than a given period. Your motion changes 'where' you are. But the problem is that you are not the only thing that’s moving. When the car that you are in is moving, coincidentally, the earth is moving around the sun as well. Without a frame of reference, the ‘where are you' question is pointless.

Motion of the Earth

As you keep making the frame of reference larger, your location in space starts getting a bit intricate. Though sitting in your room might feel like you are being still and motionless, you are not. Earth spins on its axis at about 0.5 km/s at the equator, and this speed gets slower and slower as you keep moving away from the equator. This rotational motion of the earth is what gives us night and day, and while doing so, the earth moves your spatial position as well. But the earth also traces a path around the sun. While it’s in orbit at a speed of 30 km/s[1], its spatial position changes to the sun. But the story doesn’t end here.

Space is unimaginably vast, and the sun, which is relatively the only stable entity in the solar system, is also in constant motion in an even larger frame of reference. The entire solar system moves around the center of the Milky way at an average speed of 230 km/s[2], and in that frame of reference, the sun has only completed 20 revolutions around our galaxy since its birth! And, you guessed it, the galaxy isn’t stationary either. Amongst the local group of 20 galaxies, the milky way is moving too, but where is it going?

It turns out that our sister galaxy, Andromeda, is moving towards us at about 110 km/s[3]. The neighboring galaxies, including Andromeda and about 100,000 others, are part of a bigger structure called the Laniakea supercluster[4], Laniakea, which translates to immense heaven in Hawaiian. All these galaxies are hurtling towards a mysterious region in space, blocked by the plane of our galaxy. This gravitational anomaly could possibly be the center of the Laniakea Supercluster and is known as the Great attractor[5], which is arguably the coolest name ever in astronomy. But even the reference frame of the great Laniakea supercluster is insignificantly small when we size up things to the universal scale. Now the reference frame becomes the Cosmic Microwave Background[6], the background radiation left from the big bang, the ultimate reference frame.

Hubble telescope focusing on the great attractor, a mysterious gravitational anomaly causing entity — Hubble Focuses on "the Great Attractor"/ source:ESA/Hubble & NASA

The endless horizon of the universe

Pointing our telescopes skywards is similar to looking at the horizon from the middle of the ocean. It’d look the same distance in all directions, and you'd almost feel like you are at the center of the ocean. But you know that you are not. This is exactly the case with Earth, a mote of dust in the cosmic ocean. It feels like we are at the center of the universe because we are stranded in the cosmic ocean, which is the universe. But the universe has a unique property that makes it unfathomably huge—unlike the oceans, it is expanding.

Scientists hypothesize that a mysterious energy permeates in the vacuum of space, and this expansion is caused by it. It was coined dark energy[7], and apparently, it accounts for 68% of the universe. While on ‘small’ scales, gravity prevails to bring galaxies together into groups and clusters, on larger scales, it has no effects on this entity, which is presumably a property of space itself. The cosmic inflation theory[8] put forward by Alan Guth makes the ‘where are you?’ even more trivial. The theory estimates that the entire universe could possibly be around 100 sextillion times[9] bigger than our observable universe, roughly equal to the ratio of the size of the observable universe to Earth.

The point is that space is constantly expanding, and even if gravity attracts matter, matter is part of space, and therefore, it is part of this expansion too. Our location is bound within coordinates, which are always in motion, and thus, we do not belong to a definite coordinate in space. But there’s one thing that we could do to bring back some significance to our spatial position.

The thing that matters

Our reality is made up of three dimensions, length, width, and height. Even though our eyes contain screens that are only two dimensional, fortunately, the brain makes sense of the world around us, by adding depth to these 2-d images. But dimensions don't explain the entire picture. Think of it this way. When you want to define your location to someone, you use three pieces of information, the latitude, the longitude, and the altitude, which translates to the spatial dimensions. But if you are expecting to meet someone at this coordinate, these three pieces of information would feel incomplete, unless you provide a vital fourth piece, the one that imparts sense to your coordinates. The ‘when’ part. In other words, the element of time. Time always weighs in, no matter what the coordinates are, even if the time coordinate is not provided, it is always implied because it's embedded within space.

the arrow of time which represents the unidirectional flow of time — The arrow of time/ Credit: NASA

But this concept of ‘space woven in time’ wasn’t always part of the same coin. Hermann Minkowski, Einstein’s teacher, was the one who suggested that space and time could be considered as a continuum[10]. Einstein used the concept of space-time and approached the idea of gravity from a different perspective, only to understand that gravity is caused because of the curvature of space-time.

We are all prisoners of time. The second law of thermodynamics is all about the irreversibility of entropy in the universe. Arthur Stanley Eddington[11] connected this irreversible increase of entropy to time and coined it the 'arrow' of time. For every single thing in the universe, there is a distinct past, a present, and a future, and this distinction of time is what gives space meaning. And in this ever-expanding universe, space might not care ‘where’ you are at all, but don’t worry about it too much, because time does.

Where are you?

Motion of the Earth

The endless horizon of the universe

The thing that matters

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