Monthly Archives: November 2012

If I asked you if you have ever heard of a “compressed star” or a frozen star would you know what I was talking about?

What if I said a Black Hole. Now you know where I’m going with this. It seems like a pretty suitable name. Black because no light is emitted from them, and hole because anything that falls in won’t get back out. The name compressed star is actually more suitable in some ways, giving insight into what a black hole really is. If you took any star and compressed it to a small enough volume, its gravitational pull would be great enough for it to be a black hole. A little more on this later; first, a little bit about these “black holes.”

A black hole obviously fits into its own category. Some consider them to be formed by stars but that really doesn’t matter too much. A black hole is formed when a significant amount mass concentrated into a small enough area, creates a gravitational pull so strong that even light cannot escape it. Now you may be thinking, how, if light can travel through space at such immense speeds without needing a medium, can it be sucked in by anything? This is because of the nature of the spacetime in which our universe exists, the “fabric” of spacetime. The name black hole is slightly deceiving because it is not an actual hole in the fabric of spacetime. I will explain this more in a later post, but Einstein described gravity in his general theory of relativity as the bending of spacetime fabric. The greater the mass, the greater the effect on the fabric. Black holes have such large gravitational pulls, causing a bending in spacetime that creates a curvature approaching infinity. This is why light cannot escape.

Now black holes don’t just go around sucking everything into them; we wouldn’t have a universe if that were the case. Black holes have what has been termed their event horizon – “the one-way surface of a black hole; once penetrated, the laws of gravity ensure that there is no turning back, no escaping the powerful gravitational grip of the black hole” (Brian Greene). Once inside of the event horizon, all mass is ripped to shreds as the increasing gravity pulls at such a drastically higher rate at the close end than the far end that matter closer to the center of the black hole is accelerated faster than matter just a minuscule distance further out.

Outside of the event horizon, though, objects and light are affected in the same way as stars affect them; the curvature of the spacetime fabric outside of the event horizon is very similar to the curvature around massive stars.

Now to put this force into perspective (other than the fact that even light can’t escape it). If you wanted to make a black hole out of our sun, you would have to compress it so that its radius was less than 0.0005% of the original. If you wanted to make the Earth a black hole, you would have to takes its radius of 3963.17 miles and reduce it to less than half an inch.

Now we’ve talked about the speed of light, multiverses, different perspectives on multiple dimensions, and even rainbows; so now I’m going to connect some of these things together, hopefully giving more insight into how these things work.

Now, we’ve talked a little bit about the possible existence of four spacial dimensions. The “Flatland” example gives some insight into this and into the possibility of multiple universes existing at once. We know this is all purely theoretical, so what would you say if I told you we actually live in a four-dimensional universe. Well guess what? I’m not just messing with you.

Our universe exists in the 4D world that is termed spacetime. That is the three spacial dimensions that we all know and love plus the fourth dimension of time. So the four dimensions in this case do not pertain to flatland and multiverses and all of those fun mind-boggling concepts because it is not a fourth dimension of space. These four dimensions are used instead to explain relativity.

Einstein’s theory of relativity is used to explain time dilation and spacial contraction. This is all part of special relativity which I went into in a previous post. But now, why this all works.

One of the most important implications and realizations that Einstein had when creating the theory of relativity was the concept of movement through spacetime. According to his theory, we are all moving at the speed of light through spacetime.

Because we cannot possibly imagine four dimensions, we are going to create a scenario in two dimensions. Graphically, we will put time on the x-axis and space on the y-axis. The y-dimension actually represents all motion through three dimensional space.

Now, since we are always moving at the speed of light through space time, we can start to explain time dilation. If relative motion of an object through space is zero, then all of the speed of light motion is in the time direction. As you increase your speed through three dimensional space, you increase your value on the y-axis. Because your total speed in spacetime is constant, as your speed through space increases, your speed through time must decrease. This is time dilation.

The difficult thing about this is to put yourself in the mindset that this is all still purely relative. If something is at rest relative to you, all of its speed is motion in the time dimension, but then so is yours. This means that both of you are moving through time at the same rate. Although time is always perceived the same by each person, the speed at which two people travel through time is different depending on their relative velocities.

Now for a very interesting part, think about light. Obviously it travels at the speed of light through spacetime, because all things do. But we know that light travels at the speed of light through the three dimensions of space. That means that the speed at which light travels through time is zero. From the instant the photons of light were created during the big bang, they have been moving at the speed of light through space and have not aged a single day. They are still at the exact same point in time as the big bang itself.