Have you ever looked above into the night sky and wondered about those twinkling little dots and felt humbled? A growing need to learn about the vastness of the universe and its secrets. Spending hours, are you trying to fathom the depth of the unfathomable? Well, today, to quench your thirst, we are going to be talking about black holes and time warps.
Black Holes and Time Warps
Black Holes
Let’s start today’s discussion of black holes and time warps by defining what exactly is a black hole. This is a crucial step before we dive into the relationship between black holes and time warps. It is a place in space where the pull of gravity is so strong that not even light can escape. How does gravity get so much strength? Well, because a black hole is formed by squeezing a vast amount of matter into a tiny space.
This can happen when a stellar body collapses in on itself due to gravity. When a star is dying, instead of exploding into a supernova, it gets squeezed under the weight of its gravity. This is essentially a general description of a black hole. Because no light can escape a black hole, we can’t directly see a black hole. They’re invisible. We can use space telescopes with special tools to find black holes and to study the effects of black holes and time warps.
Extending on our introduction about black holes, they can be big or small. Scientists think that the most minor of black holes can be as big as an atom. Now don’t get me wrong. They have a small size, but that doesn’t mean they have less mass. Black holes are one of the densest cosmic bodies out there. So, even a black hole as small as an atom can have the same amount of mass in them as, say, a mountain. The total amount of matter in a black hole depends on the amount of concern that the parent star had.
The other side of the spectrum has stellar black holes. These have masses up to 20 times more than the sun. The biggest of these types are called supermassive black holes like the one in the center of our Milky Way Galaxy holding it all together with its immense gravitational attraction. These black holes are like one million suns together tightly contained in a black hole. Ours is called Sagittarius.
Non-rotating Black Holes
A black hole’s sphere of gravitational influence extends undiminished over its event horizon. After that radius, it usually acts like any other cosmic body. Let’s suppose a spacecraft was to travel near a black hole, for whatever reason, maybe to gain velocity by slinging around it.
As it approaches the event horizon, the curvature of spacetime gets so extreme that time is slowed down by a lot. Now it would take precise calculations to measure how much, but suffice to say that a few generations may have passed on earth in the meantime.
Now comes the exciting part, what happens once you cross the event horizon? Well, there is no coming back, you cannot come back if you’ve passed it and your fate is sealed, Gravitational forces are incredibly strong, and you will get pulled towards the center.
A phenomenon called spaghettification occurs. The gravitational forces are so extreme that you get stretched like spaghetti, hence the name. Also, the role of time and space gets reversed when inside the event horizon. So basically, as you keep approaching the center of the black hole, you are moving through time and not space, and the passage of time is seen as moving through space.
Once you reach the singularity point at the center of the black hole, you cannot move, as per common sense, but since moving towards the center was actually walking through time and not through space, the laws of physics break down, at the singularity point, and hence its name. There is no coming back from this point.
The fate of the information that you carried is highly debated in today’s world, whether it is preserved or destroyed. There is even a chance that that information ends up in a lower-dimensional universe inside the black hole, or is spit out from a connected white hole.
And to any external observer, you will be an image who will see you slowly descending into the black hole, with your rate of descent getting slower as you move further in. Your image will be redshifted progressively, and to them, your image will linger on forever.
Rotating Black Holes
The center of a black hole is the point that is guarded against human observation by the event horizon. For a long time, black holes were assumed to be not rotating. So, their singularities were considered to be just points.
Now that we have discovered that black holes rotate, current models tell us that the singularities are infinitely thin rings. This segues us into how the event horizon seems. So, this rotating phenomenon leads to the event horizons to appear oblong, that is squashed at the poles, and bulging out at the equators.
Event Horizon
To have a rotating black hole, the event horizon comprises an outer horizon and an inner horizon. The outer horizon pretty much acts like the event horizon of a non-rotating black hole, that is the point of no return. The inner horizon is a lot stranger. Once past that threshold, laws of physics break, just like they break past the event horizon of a non-rotating black hole.
Now for a spinning black hole, the black hole drags the fabric of spacetime around with it, much like any other rotating cosmic body. This is also known as Frame dragging or the Lense-Thirring effect. This effect creates a cosmic whirlpool, which physicists call the ergosphere.
This effect takes place outside the event horizon, and this makes the bodies revolving near the black hole to move in the same direction as the spin of the black hole. This alludes to the previously stated fact that any spacecraft could use this to gain speed to perform a slingshot operation and can escape the gravitational pull of the black hole.
Since we can’t directly study a black hole, it is generally studied using what is called an accretion disk, a large disk of particles revolving around a black hole. In-depth studying can tell us a lot about the event horizon, and help us study the nature of black holes.
Apparent Horizon
Enough about the event horizon, let’s talk about the apparent horizon. This surface lies within the event horizon. To imagine this surface, imagine a transparent sphere with a point source light at its center. Light is being radiated in all directions. So, the light is divergent if we stand with our back to the black hole.
Now keeping our positions, if we were to move into the sphere, there would come a time, when we’d notice the light not being divergent, but the different rays are parallel to each other; this is the apparent horizon, and beyond this point, the light rays would appear convergent.
Resolving Information Paradox
Here’s an interesting take on the practicality of black holes. So, when a massive cosmic body collapses onto itself, there are two opposing forces that act, radiation pressure and gravitational attraction.
See, as the body is collapsing onto itself, as the particles are getting smashed against each other, with ever-increasing densities, heat builds up. This tremendous heat opposes the force of gravity from making the body collapse totally and is known as radiation pressure. This creates a quasi-black hole which is different from Einstein’s mathematical pure black hole.
As gravity and radiation pressure oppose each other, no true event horizon is created, and we find an apparent horizon is created. As mass gets converted to energy and is radiated away, slowly, the quasi-black hole reduces in bulk, and by the time the actual event horizon forms, the mass has been reduced to zero, which satisfies Einstein’s equations.
But by then, as you may have noticed, the structure is no more, and the spacetime curvature has returned to being flat.
This resolves the information paradox proposed by Stephen Hawking, which you can read more about here: How Particles Escape Black Holes, Information Paradox.
And this is how an Indian scientist Abhas Mitra, resolved the paradox much before Stephen ever did: Abhas Mitra and the Information Paradox. It’s a beefed-up version of what I say here.
Time Warps
Now that we are done with the mysteries regarding black holes, let’s talk about what time warps are, the second component in our relationship of black holes and time warps. In a nutshell, it means the speeding up or slowing down of time.
Now in our universe, time can be sped up or slowed down in two different ways, which are derivations of the same phenomenon, that is, gaining a higher value of the stress energy-momentum tensor, but let’s not get ahead of ourselves.
Time warping or time dilation can be caused by speeding up the velocity of a moving body in space, and the effects can be realized when we are moving at speeds near to the velocity of light. It can also be caused by increasing the gravitational attraction in an area of space. Both these cause the speed of time to be slowed down.
Since we are talking of black holes and time warps, it makes more sense for us to talk about the gravitational effects, to be more in line with how black holes and time warps are related.
Einstein’s Gravity
Now, if we are to understand time warps, we have to first understand the concept of Einstein’s gravity. Unlike Newtonian gravity, Einstein’s gravity exists in a space that can bend and stretch and do all kinds of crazy stuff. So, gravity is formed by the presence of a mass in spacetime or the very fabric of the cosmos.
The higher the amount of mass present, the higher will be the curvature of spacetime at the surrounding places, and the higher the gravitational field because of the curvature, and the body also drags the spacetime fabric around itself as discussed earlier.
Thus, we can say that anything with mass can warp time. But it only becomes apparent or noticeable when we can perceive it, because of its magnitude, such as near a black hole. The bigger the mass, the more the time warp.
Observation of Time Warps
However, it has to be noted that time warp is relative. It is only noticeable for an observer for whom time is running on a different speed than yours is. If you were to go near a black hole, you wouldn’t feel the effects of time warp.
Still, an external observer whose time is not relatively slowed down will see that you have slowed down proportionately according to the amount of time warp you are undergoing respect to his time frame.
Cause of Time Warps
Time dilation is the ultimate effect of increasing the amount of energy a body possesses, which leads to increased spacetime curvature. In two ways, can we gain strength?
According to the Quantum Field Theory, we can either move faster, increasing our total kinetic energy or you can interact with a field, for example, an electromagnetic field. The stronger the interaction we have with our field, the stronger the gravitational field becomes because the stronger the spacetime curve becomes.
Another interesting fact to consider is that mass isn’t precisely what causes gravitational fields. That’s just an oversimplification. This is where the energy stress momentum tensor value comes to play. Any increment of the tensor value in a system of particles leads to the system having a higher energy value because one of the ten components of the tensor value is energy.
General Relativity, the principle that governs this phenomenon, doesn’t discriminate in what kind of energy is used to increase the tensor value. The more the power, the higher the equivalent mass of the system, not to be confused with the particle mass as a result of interaction with the Higgs Field.
Higgs Field
It is a field of energy that is thought to exist throughout the universe. This field is accompanied by a fundamental particle called the Higgs boson, which interacts continuously with other particles such as electron and proton. It gives them their particle mass, which is different from the mass that a body gains from the binding energy it possesses.
Higgs field does not create mass, which would be a violation of the laws of conservation. Particles gain mass by interacting with Higgs boson in nature. Also, the faster a body moves in spacetime, the stronger it interacts with this field, and the more particle mass it gains, which causes it to never reach the speed of light.
Understanding the Effects using a Proton
If we are accelerating a proton in a particle accelerator, a few things happen as it begins to approach the speed of the light. But for that, we have to know that even a proton, is a system of particles, made up of two up quarks and one down quark, that are held together by gluons.
As the proton approaches the speed of light, the interaction of the quarks and the gluons with the Higgs field increases, which increases the particle mass of the proton as a whole. However, this interaction doesn’t lead to the rise in the curvature of spacetime or time dilation.
What leads to time dilation is the very high value of kinetic energy in the system which causes a very high amount of energy in the stress energy-momentum tensor, and leads to the proton experiencing velocity time dilation.
If we had to make this proton experience gravitational time dilation, we had to bring it near a massive body, that is a body, with a strong spacetime curvature near it. This would be equivalent to making the proton interact with a high energy field, which contributes to the energy of the proton particle and makes it undergo time dilation.
And with that, we have come to the end of our topic on black holes and time warps.
Good Hunting!!
So, there you have it, that’s a very in-depth, but hopefully easy to understand the discussion about black holes and time warps, and even a teeny tiny bit of Higgs Field. This is just the beginning; we have a fantastic journey ahead, into the world of black holes and time warps.
As a bonus for making it this far, here’s a video on wormholes, a spacetime structure that arises from black holes some of the times.
Also, if you liked reading this article, you can check another one of mine, where I talk about 15 Cool Things About The Universe.