Pre-Ramble:
It was the fall of 2005, and it was not the first time in my adult life that I had risked too much and lost everything and had to move back in with my parents. This gave me plenty of time to sit and think deeply about things. The usual things came to mind at first, as one might imagine in such a scenario, but then one day I decided I needed something new to occupy my mind.
I am not a scientist. I did not study astronomy or physics at a college level. But, like many people, I do thoroughly enjoy reading about the new discoveries that keep getting made in these fields at ever increasing frequency. I do not profess to have any answers, only some specific questions that I WOULD LIKE TO ADD TO THE CONVERSATION.
Since Dark Energy and Dark Matter were such new concepts back in 2005, many great minds had all kinds of ideas – and no ideas – about what they may be. In that respect not much has really changed in the last ten-plus years. Many had then, and still now, wonder how much of our knowledge of the universe will need to be completely rewritten to integrate these two new phenomenon into our paradigm of the universe.
The episode of thought from my parents livingroom that has led to this blog post so many years later started like any other thought experiment. But in my case, my thought was that we should consider Occam’s razor in our attempt to explain these two new forces.
Consider these two scenarios:
First, we have lived in and studied this universe from our particular vantage point and discovered many, many things over the centuries. But, somehow, two previously completely unknown forces have revealed themselves to not only make up most of the universe, but together they make up ninety-some percent of the universe. And we never had any inkling that they were there. None. They were a complete surprise, and now we have to rewrite everything that we think we know to include them in our understanding as a whole.
Or, second. These two new forces, perhaps, just maybe, are things that we have already discovered. They are just playing out at a level that we are not familiar with and couldn’t have foreseen possible from our vantage point on a tiny rock floating in the middle of it all.
So this was the start of my thought experiment for Dark Energy and Dark Matter: Could they be explained, at least in part, by previously unimagined actions of forces that we do already know about, but happening at a level that we previously did not understand possible? This blog post will focus on the shot-in-the-dark hypothesis that I framed to explain what makes up Dark Energy (Dark Matter post to follow later).
So, what is Dark Energy? (Well, we don’t know.)
In the olden times of astronomy up until the early twentieth century it was commonly accepted and believed that the universe was made up only of the Milky Way (galaxy) and that it was a constant, stable, and relatively unchanging place. Then in the 1920’s Edwin Hubble was able to show that the universe not only contained other galaxies that were separate from the Milky Way, but that these other galaxies were – for the most part – also moving away from the Milky Way. In short, it was discovered that the universe was larger than previously thought and it was also still expanding and getting even larger.
This discovery gave us the theory of the Big Bang. Since we could now see and measure that virtually every galaxy in the universe was indeed moving away from us, if we were to rewind time and go backwards, the galaxies would be getting closer to us. If this rewound back as far as it could go it would suggest that all of the galaxies were once together in the same place as each other. The energy from the Big Bang created the force that made these galaxies move away from each other.
For the near-entire remainder of the twentieth century most scientists believed that this expansion of the universe must be slowing down, that the effect of gravity must be acting against the expansion. Much later, in 1998, some scientists, working to try to measure how much the expansion was slowing down, discovered something completely unexpected: The expansion was not slowing down at all. Even more puzzling it was actually continuing to accelerate.
The search to explain what force could possibly be making the expansion of the universe continue to accelerate is the search to understand Dark Energy. Dark Energy is widely considered to work against the force of gravity and repel matter. And it is this repellent force that we now call Dark Energy. We call it “Dark” Energy not because of an absence of light, but because it is so unexpected and mysterious we can’t put a finger on what it could be – it seems to go against everything we thought we understood.
Hypothesis: Could Dark Energy be some sort of “Reverse” Gravitational Time Dilation Effect?
Science has documented that space-time dilates. General Relativity says that the closer you are to a heavy mass, such as Earth, the slower time will move for you. To go to an extreme on this point, theoretical physicists believe that the closer one gets to a black hole’s event horizon the slower time would move for you until it seems to come to a virtual stand-still.
We have already directly measured this phenomenon with the clocks on-board a satellite in orbit above Earth running slightly faster than an identical clock on the surface of Earth.
More extreme (not considering for the counter-effects of Special Relativity) the clock on the Voyager 1 spacecraft, which has been steadily moving away form the Earth since 1977, should now be about 10 seconds or so ahead of us here on Earth. But it’s not just that Voyager 1’s clock is now running 10 seconds fast; Voyager 1 has actually experienced 10 more seconds of existence in the universe than we have experienced back here on Earth since its launch on September 5, 1977.
This happens because our Sun has created a gravity well in the fabric of space-time, like any other heavy mass object in the universe. The gravity well that the Sun has created is in relation to its total mass. Other heavy mass objects also make gravity wells relative to their total mass. This means that the gravity well made by Earth is much smaller than the Sun’s, but the gravity well created by a super-massive black hole (like the one at the center of the Milky Way) is much, much larger than the Sun’s.
Interstellar space within the Milky Way, the space in-between stars like our Sun, would have extremely negligible gravitational pull form our Sun or other stars, and someday Voyager 1 will pass out into this part of space-time. Many may believe that then the rate of space-time would arrive at “zero”. But would it? Still have some effect of the Milky Way galaxy and it’s gravity.
Kuiper belt is a disk of smallish objects that were leftovers from the formation of our Solar system 4.5 billion years ago. These are objects from the size of the dwarf planet Pluto all the way down to tiny pebbles of debris. This belt extends out from the edge of our Solar system, and it is in the Kuiper belt where the Voyager spacecraft is currently traveling.
So let’s consider this: A tiny Kuiper Belt object the size of a golf ball that has been floating around the edge of our solar system since its formation is not the same age as the Earth. If in the last 39 years Voyager 1 has managed to become 10 seconds or so older than us, then this tiny golf ball that has been in less gravity than the Earth for the last 4.5 billion years is now something in the neighborhood of 40.7 years older than the Earth. Meaning that that little golf ball has experienced around 40 more years of existence in the universe than the Earth has experienced.
This extra time that our golf ball sized Kuiper belt object and the Voyager spacecraft have experienced didn’t just happen all at once. They have been experiencing more time going by all along. Its hard to understand, I know. But when an hour goes by for us here on the surface of Earth, a little bit more than an hour has gone by in the Kuiper belt area of our solar system. It’s only a tiny, tiny bit longer than an hour, to ballpark it for every single 1.000 hour even that goes by on Earth 1.00000000995911331298 hours goes by in our golf ball object’s neighborhood. The difference is too small to be perceived by humans but it does add up or time, for every 3.18 years that goes by here on Earth objects in the golf ball object’s neighborhood experience one extra second. But again, that one extra second doesn’t just get added on every 3.18 years. It happens continuously all the time, it’s happening right now, it happened yesterday and it will happen again tomorrow.
So if we know that space-time moves at different speeds in relation to gravitational mass. And we believe that space-time can, in fact, dilate to a near stand-still in the presence of super-massive objects. Then why could the opposite dilation effect not be possible in the “super-absence” of gravity? Why would we assume that Voyager is now moving at “zero” on the dilation scale? Perhaps there is more to the dilation scale than we have previously thought possible?
Intergalactic space-time, the space in-between galaxies, would be the equivalent of leaving the outer edges of the Milky Way where there would be a negligible gravitational pull from the Milky Way or other galaxies. Outside of any galaxy there should be less gravitational effects from the gravity wells created by galaxies.
If this were to be true, it would mean that more time goes by in interstellar space than goes by on Earth during the same period. Meaning when we experience one hour here on Earth, more than one hour goes by in areas of space-time where there is less and less gravity. If Voyager is experiencing 0.00000000995911331298 more time every hour than it could be that with even less gravity in intergalactic space the effect is even greater.
So here is the Dark Energy connection. If the universe has always been expanding at the same rate of speed from the beginning, as was assumed for much of the twentieth century, but in areas between galaxies more time is going by relative to inside the galaxies, then the result would look like an acceleration to an observer inside the gravity well of one of these galaxies.
Let’s use an example that most people would understand. Let’s take the distance that an automobile going 60-miles-per-hour would travel in one hour of time (as it’s measured on Earth). On Earth the math is easy, it would go exactly one mile. But in a part of space-time were time goes longer than on Earth, that automobile would travel for longer than one Earth-hour. Even though it is still going the same 60-miles-per-hour it would travel that speed for more time.
If less and less gravity makes space-time dilate more and more, than this effect would start to have a compounding effect. If we had one hour of universe expansion here on Earth, and, let’s say, one hour and one minute of expansion at a point in intergalactic space then there is actually more space created from the expansion in the intergalactic area. And this extra one minute of space created is also expanding at the same rate. Over billions of years this would add up to very vast areas of space that are being created in intergalactic space just due to the extra small amount of extra time that passes in that area. And again, all of the extra area of space created is also expanding at the same rate.
Could this effect possibly be what we are now trying to describe as Dark Energy? To tell you the truth, I have no idea. But it sure is fun to think about.
