Is gravity the “friction” of space-time?

Intro

Ya’ll’ve probably already seen Christopher Nolan’s movie Interstellar, right? Good. Well, regardless of how you felt about the movie’s conclusion that ‘love conquers all’ (which, honestly, it probably conquers most), there was some pretty good science on screen. Particularly, I loved how the movie touched on the understanding that time can pass more quickly or more slowly. In other words, time can pass at different rates for different people (under the right circumstances, that is). In the movie, Nolan does a fantastic job illustrating how characters on a planet near a black hole, experiencing tons of gravity, would experience time slower than people, say, on Earth (which has comparably less gravity). You see, time has a speed. Time has a rate at which it passes. Like a velocity. To us, it always feels like time is passing at the same rate. But that isn’t exactly the case. If we were moving closer and closer to a massive object with large gravity, for example, to an outside observer watching us, we would appear to be moving in slow motion. Alternatively, we would appear to be moving in fast motion to an observer who is much closer than us to a massive object. Scientists have also measured that this sort of time dilation is measured for objects traveling near the speed of light. So it isn’t just large amounts of gravity that warp time, but incredibly fast speeds also have this effect. We can observe this phenomenon when we track satellites in Earth’s orbit. We find that their internal clocks move at a different rate than our clocks here on the Earth’s surface. This is because they are moving through space at a much quicker rate that we do on the surface. Our calculations tell us that as an object gets closer and closer to the speed of light, it experiences time at a slower and slower rate. For an object moving at the speed of light, it can travel billions of lightyears without experiencing the passage of time at all. There seems to be a fundamental “give and take” between the dimension of ‘speed’ and ‘time’. In other words, to have more expression in one dimension, say ‘speed’, is to have less expression through another, say ‘passage of time’. It’s as if there is a cumulative cosmic ‘speed limit’ for how fast you can move through space and time.

So What?

Below, I want to make the case that objects move through time a lot like an object moves spacially in a straight line, that time has a certain “speed” it passes at, and that objects can be accelerated or decelerated through time. I argue that large repulsive events like the Big Bang and large repulsive forces like Dark Energy have created space, and are continuing to accelerate our movement through time. And finally, I theorize that gravity can be thought of as a type of ‘friction’ that will ultimately bring our movement through space-time to a rest.

The Theory

Some Questions That I Address:

Is time even stable (at a current speed)? Or is it accelerating and decelerating? Does it take energy to move through time? Does an object’s mass affect its ability to be accelerated through time? Does gravity act as a type of friction against the movement through time?

Summary of Theory:

Perhaps gravity should not be viewed as just ‘slowing down’ time in some linear fashion. That is, to be near a massive object is to forever experience time as a certain rate. Although this is an accurate way to think about time near massive objects, it doesn’t pay enough regard to the idea that mass attracts other mass. That mass accumulates because of gravity. And that to be a near a massive object is to have time slow down around you as it accumulates more and more space debris. Instead, it should be viewed as the cosmological equivalent to friction that is decelerating motion through all dimensions, including time. One way to think about the universe is that it’s ‘trying’ to settle. To find a resting spot. More accurately, the universe is trying to relieve pressure. Much like the balance between attractive and repulsive forces. A proton and an electron. A wave’s crest and it’s trough. The highest know order of energy that we know of is what we call ‘mass’. In fact, mass can be thought of as just a measure of energy: m=E/C² Mass is the most stable, higher order, resting place of energy. Theoretically, a universe of only mass could have no kinetic or potential energy, no space, and therefore no movement through time. So what’s the deal? 1) I propose that unstable, repulsive energy is what has separated mass in the first place (think Big Bang). This unorganized, imbalance of energy created space as we know it. And allowed for the passage of time. 2) After our universe’s kinetic energy from the big bang has separated out matter, gravity began to consolidate much of that space debris into massive galaxy and star systems, converting kinetic energy into thermal energy. 3) Despite gravity slowing down momentum from the big bang, we see that galaxies are beginning to accelerate away from each other–possibly a by-product of thermal energy (like emitted massless particles that have momentum, like photons). 4) Pressure from this thermal energy will dilute as galaxies grow more distant. Dark, cold, and alone, galaxies will begin to implode on themselves, creating super massive black holes. With no more expansive forces in the universe, gravity will lightly tug on these distant galaxies, slowly decelerating the expansion of the universe, and consolidating more and more dead galaxies in a more massive black hole. 5) Spacetime will be destroyed (as it was created) during this deflation. And every remaining parcel of space will have increasingly more gravity acting upon it. Time will slow. And energy will be more organized into this higher-order thing we call ‘mass’ at the center of an increasingly dense black hole.

Why might this happen?

Part I: Understanding Gravity & Space-Time

Our 3-D World

Often, we think about forces, energy, and friction only in terms of objects in our 3 dimensional world. We think in terms of up/down, left/right, forward/backwards. Right? We understand that when an object is in motion, a force must have been applied to it. Let’s imagine pushing a ball with mass in a straight line:

• If we push a ball and then we stop pushing it, the ball will either begin to slow down as it encounters friction, or it will remain at a constant speed if it’s in the vacuum of space. Newton’s Laws, yo.
• If we apply a continuous force on the ball, the ball could be accelerating, maintaining it’s speed, or even slowing down. Whether the ball is speeding up or slowing down is a balance between our pushing it and the resisting forces like friction.

When a ball has friction slowing down it’s movement, we must maintain a continual force to maintain it’s velocity. If a continual force isn’t applied, the ball will come to a rest. But that’s not the whole picture. There is a fourth dimension that we move through.

Understanding Our 4^th Dimension: Time

So here’s the question: Does not our fourth dimension, time, also requires energy to move through it? Is the passage of time not also a rate? Just like speed? Is there a “velocity” of time? Well, yes, we understand that the speed of time isn’t fixed. And that things live gravity and speed affect how quickly time passes. If we think of time in this way, as similar to any of our first 3 dimensions, would it be surprising that the mass of an object could affect its ability to be accelerated through time? Think about how time moves slower while near a black hole, like in our example Interstellar.

Space = Time

We know that the passage of time is tied to the existence of space. Where there is space, there is time. “Space-time”. One and the same. Without space (without the area between particles and things that we consider to have mass), there is no passage of time. With little space (matter jam packed, so it displaces space), we have slower time…like the center of a black hole. The argument goes that, conceivably, if matter is packed tight enough, we would have no room for space (and therefore no room for time). Theoretically, dense matter like this exists at the center of black holes. And because there is no room for space, this matter exists in at a single moment in time. Stuck in the moment it was consolidated and organized. We call this a Spacetime Singularity.

Gravity and its effects on Spacetime

I suggest that, like an object at rest in the 3rd dimension, objects do not naturally move through the 4th dimension without first having energy applied. That is, a force must have been applied to get it going. That repulsive forces during the Big Bang have acted on mass to create lots of space. In this model, we can think of gravity as the mechanism slowing down the creation of space and time despite other energies working against it (think Dark Energy, expanding the universe against gravity, creating more space that allows for the passage of time). For this reason, I find it useful to think of gravity as the “friction” against movement through our 4th dimension, time.

Is gravity truly a force? Or just a numerator?

Why is gravity considered a ‘force’ against time? Why doesn’t gravity just reduce the speed of time by some factor? I mean, if I’m on Earth, I’m certainly experiencing gravity. But time doesn’t appear to be gradually slowing down for me. Well, sure. The reason I argue that gravity is decelerating time, not just making it slower, is because mass attracts mass.

What if mass didn’t attract other mass?

Let’s imagine a universe where gravity doesn’t attract objects to each other. And let’s pretend that we experience time passing on Earth a rate of X, and that we can measure time near a black hole passing at, say, (1/2)X. In this example, time would just continue forever. For 100 years passed on Earth, only 50 years would have passed near the black hole. But neither rates would ever slow down. The passage of time is very linear in that fashion. This mental model doesn’t seem inherently wrong. I mean, if mass moved through time at a linear speed, neither accelerating or decelerating, it would be analogous to an object moving through space, never encountering friction…This is how most people tend think about the passage of time. As ongoing. At a constant rate. Forever.

But mass does attract mass.

But gravity does attract other masses. In fact, it’s a feedback loop: Gravity attracts more mass. More mass increases gravity. More gravity attracts more mass. And so on. This doesn’t mean that two objects combine to have greater total gravity. But it does mean that their center of masses move closer as they accumulate. And so the pull on more distant objects become magnified. But what’s also important here is that more mass and gravity means more density. And more density means that time is more warped by gravity at the surface of the object. Slowing time. When two masses are operating at a distance, they are slowing each other’s time down. And since they are attracted to each other, time on the surface of either object is increasingly slowed down as they approach each other.

Part II: “Dark Energy” & The Expanding Universe

Understanding that light has momentum, and therefore pressure

We understand that although light photons don’t have mass, they do appear to have momentum. That is, they exert a sort of pressure on a surface. You might say that if a photon hit you square on, it might knock you back a little bit. Okay, not really. But that is why we are able to have “solar sails”. Solar sails (also called ‘light sails’ or ‘photon sails’) work a lot like the sails of a boat. Photons traveling through space, interacting with the reflective material of the sails, exert their momentum on the sails, creating propulsion. This is considering a cheaper and longer lasting solution to jet propulsion, which requires fuel and more moving parts. It stands to reason that emitted light from stars, traveling through the vastness of space, is waiting to run into other objects that either absorb the light as heat…or repel the light. Other objects like, you know, a mirror, or another star.

So can light explain the effects of Dark Energy? It’s a theory. Let’s run with it.

One theory I have then is that Dark Energy, expanding the distance between galaxies, is just particles (perhaps these light photons) that are pushing all galaxies apart. Like a sort of pressure. This is similar to a balloon expanding as you blow air into it–the higher pressure inside of the balloon expands the surface area to equalize the pressure inside and outside of the balloon. This “pressure” is simply creating more space in the universe. And remember, creating space continues to allow for the passage of time. It’s possible that the repulsive forces during the Big Bang may have created much of the space in the universe. But as gas clouds formed stars, the emitted light has begun to push galaxies apart. This would reconcile with why we don’t see the expansion of the universe decelerating.

Why are galaxies getting further apart but closer objects aren’t?

Remember that a light photon would exert the same amount of momentum on an object regardless of how far it traveled. However, the forces of gravity drop off precipitously over distance: F = G*M/R^2. As the distance (“R”) between two objects gets larger, the force of gravity (“F”) gets smaller at an increasing rate. It may be that closer bodies (like stars within a galaxy) are close enough that gravity is a stronger attractive force than light photons are a repellent force. But that between galaxies, the forces of gravity fall off so precipitously over such great distance that the massive amount of pressure caused by emitted light is pushing everything away stronger than gravity can hold everything together.

Part III: What is the fate of our universe?

If it were the case that the emissions from stars (like photons) are responsible for ‘pressure’ that is expanding the distance between galaxies, then here is a plausible prediction for the fate of the universe: it collapses, and possibly starts over.

Where does all the energy go?

It seems like the expansion of the universe can’t go on forever. I mean, if dark energy is energy, it will be exhausted as it turns into kinetic energy. That is: the kinetic energy of massive galaxies moving away from all other galaxies. It seems popular to discuss the expanding universe as if will it just accelerate outward indefinitely. That is will just grow colder and darker… But remember, as far as we can tell, energy can’t be created or destroyed. So all of that stored energy in stars have to go somewhere when the universe is burned out. Energy has to exist in some form after all of the fire is gone. As dark energy becomes absorbed and diluted. Where does all that energy go? Potential energy. (The type of energy something has when it has the potential to fall and have gravity act on it). So now imagine the universe is pushed out very, very far. It’s cold. And dark. But gravity (potential energy) reaches out holding these stars together over infinite distance…

The great collapse of our universe

As galaxies have become further away, dispersed light (our proxy for ‘dark energy’) will have less repulsive effect on them. Gravity, however, reaches out over infinite distance. Slowing down the rate of expansion. In this theory, the expanding universe will eventually be accelerating outward at a decelerating rate (Second derivative. Nuts, right?). It follows that:

• galaxies will continue to burn through their energy, eventually becoming cold and dark
• galaxies will collapse into themselves, creating super massive black holes
• galaxies will begin to collapse into each other creating even larger, more dense black holes
• deflation of the universe will destroy space as easily as it was created, and all celestial bodies increasingly collapse into one mass

What does it all mean?

Gravity, with its infinite reach, will begin to collapse all of these dark, dead galaxies (like a deflating balloon) into an increasingly massive singular object. This object will be so dense that there is no room for space or time. Either all energy will organize under a higher order of energy we call ‘mass’… or the chaotic imbalance of attractive and repulsive forces may be the starting of another Big Bang. Thus continuing the eternal ebb and flow of the universe. …but, you know, this is just a theory