Posted on 06/12/2025 9:35:23 AM PDT by Red Badger
About a century ago, scientists were struggling to reconcile what seemed a contradiction in Albert Einstein’s theory of general relativity. Published in 1915, and already widely accepted worldwide by physicists and mathematicians, the theory assumed the universe was static – unchanging, unmoving and immutable. In short, Einstein believed the size and shape of the universe today was, more or less, the same size and shape it had always been.
But when astronomers looked into the night sky at faraway galaxies with powerful telescopes, they saw hints the universe was anything but that. These new observations suggested the opposite – that it was, instead, expanding.
Scientists soon realized Einstein’s theory didn’t actually say the universe had to be static; the theory could support an expanding universe as well. Indeed, by using the same mathematical tools provided by Einstein’s theory, scientists created new models that showed the universe was, in fact, dynamic and evolving.
I’ve spent decades trying to understand general relativity, including in my current job as a physics professor teaching courses on the subject. I know wrapping your head around the idea of an ever-expanding universe can feel daunting – and part of the challenge is overriding your natural intuition about how things work. For instance, it’s hard to imagine something as big as the universe not having a center at all, but physics says that’s the reality.
VIDEO AT LINK...........
The Expanding Universe | National Geographic
The universe gets bigger every day.
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The Space Between Galaxies
First, let’s define what’s meant by “expansion.” On Earth, “expanding” means something is getting bigger. And in regard to the universe, that’s true, sort of. Expansion might also mean “everything is getting farther from us,” which is also true with regard to the universe. Point a telescope at distant galaxies and they all do appear to be moving away from us.
What’s more, the farther away they are, the faster they appear to be moving. Those galaxies also seem to be moving away from each other. So it’s more accurate to say that everything in the universe is getting farther away from everything else, all at once.
This idea is subtle but critical. It’s easy to think about the creation of the universe like exploding fireworks: Start with a big bang, and then all the galaxies in the universe fly out in all directions from some central point.
But that analogy isn’t correct. Not only does it falsely imply that the expansion of the universe started from a single spot, which it didn’t, but it also suggests that the galaxies are the things that are moving, which isn’t entirely accurate.
It’s not so much the galaxies that are moving away from each other – it’s the space between galaxies, the fabric of the universe itself, that’s ever-expanding as time goes on. In other words, it’s not really the galaxies themselves that are moving through the universe; it’s more that the universe itself is carrying them farther away as it expands.
A common analogy is to imagine sticking some dots on the surface of a balloon. As you blow air into the balloon, it expands. Because the dots are stuck on the surface of the balloon, they get farther apart. Though they may appear to move, the dots actually stay exactly where you put them, and the distance between them gets bigger simply by virtue of the balloon’s expansion.
It’s the space between the dots that’s growing. NASA/JPL-Caltech, CC BY
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Now think of the dots as galaxies and the balloon as the fabric of the universe, and you begin to get the picture.
Unfortunately, while this analogy is a good start, it doesn’t get the details quite right either.
The 4th Dimension
Important to any analogy is an understanding of its limitations. Some flaws are obvious: A balloon is small enough to fit in your hand – not so the universe. Another flaw is more subtle. The balloon has two parts: its latex surface and its air-filled interior.
These two parts of the balloon are described differently in the language of mathematics. The balloon’s surface is two-dimensional. If you were walking around on it, you could move forward, backward, left, or right, but you couldn’t move up or down without leaving the surface.
Now it might sound like we’re naming four directions here – forward, backward, left and right – but those are just movements along two basic paths: side to side and front to back. That’s what makes the surface two-dimensional – length and width.
The inside of the balloon, on the other hand, is three-dimensional, so you’d be able to move freely in any direction, including up or down – length, width and height.
This is where the confusion lies. The thing we think of as the “center” of the balloon is a point somewhere in its interior, in the air-filled space beneath the surface.
But in this analogy, the universe is more like the latex surface of the balloon. The balloon’s air-filled interior has no counterpart in our universe, so we can’t use that part of the analogy – only the surface matters.
So asking, “Where’s the center of the universe?” is somewhat like asking, “Where’s the center of the balloon’s surface?” There simply isn’t one. You could travel along the surface of the balloon in any direction, for as long as you like, and you’d never once reach a place you could call its center because you’d never actually leave the surface.
In the same way, you could travel in any direction in the universe and would never find its center because, much like the surface of the balloon, it simply doesn’t have one.
Part of the reason this can be so challenging to comprehend is because of the way the universe is described in the language of mathematics. The surface of the balloon has two dimensions, and the balloon’s interior has three, but the universe exists in four dimensions. Because it’s not just about how things move in space, but how they move in time.
Our brains are wired to think about space and time separately. But in the universe, they’re interwoven into a single fabric, called “space-time.” That unification changes the way the universe works relative to what our intuition expects.
And this explanation doesn’t even begin to answer the question of how something can be expanding indefinitely – scientists are still trying to puzzle out what powers this expansion.
So in asking about the center of the universe, we’re confronting the limits of our intuition. The answer we find – everything, expanding everywhere, all at once – is a glimpse of just how strange and beautiful our universe is.
Rob Coyne, Teaching Professor of Physics, University of Rhode Island. He receives funding from the National Aeronautics and Space Administration (NASA) and the US National Science Foundation (NSF).
Some galaxies were slower than others!............
My house.
The center of the universe is its Ground Zero, plus or minus 1,000,000 light years or so in every direction. /s
The theory is that galaxies that are relatively local to each other can combine as a group. This'd also be why you are not personally expanding along with the universe - local effects of gravity overcome the expansion, with the caveat that this will not keep your waistline from expanding.
Here's a pic of what we're going to collide with in about 4 billion years.
There are galaxies that are gravitationally bound into clusters. Galaxies that are so bound can and do have local relative motions that overcome the expansion of space. Such galaxies can indeed move toward each other and even on occasion collide and merge. It is more accurate to say that unbound distant galaxies will always appear to be receding.
“Pass through” might be a more apt description. The stars are so far apart from each other (in factors of light years), that the odds of collision are literally and figuratively astronomical.
I believe the standard, if uncomprehending, answer is "dark energy".
No one asked me, but I'd be perfectly content to leave that question unresolved--not through lack of trying, mind you--and to simply allow God's oh-so-clever design to remain magnificently imponderable.
Thanks. I thought that author's absolute statement was questionable.
-PJ
True center? In the heart of God.
Local motion varies and can cause galaxies to interact and merge, especially in earlier phases when the universe was more dense. Since the distances involved are so vast, everything outside our own galaxy occurred billions of years ago when the universe was younger and more dense.
“...scientists are still trying to puzzle out what powers this expansion....”
What’s so hard to understand? It blowed up real good!...............
It’s a good read. I thought physicists were thinking in terms of more than three physical dimensions.
In the future there will be opinions about just how far off the mark we are today.
Several years ago I remember reading an article about some telescope somewhere which had found a small galaxy which was moving at 100,000 miles per hour, that is hour, not second but it was not moving away from us, it was to the ‘side,’ so to speak.
Well maybe, but as a practical matter that isn’t possible. Maybe because we don’t have enough observational data to determine conclusively the true large-scale topology of the universe. The data we have is consistent with a closed universe that indeed would behave as you describe. It’s also consistent with an open universe where you would never return to your starting point. The overall curvature is very close to flat, but even a flat universe can be closed. It may not look flat in the common usage of the word, but a doughnut-shaped universe would be mathematically flat. To see this imagine a very large sheet of paper - obviously flat. We then roll up that paper and join one end to the other to make a cylinder. This still is flat because we did not change the surface - no tearing or crumpling to make it curved. We can then join the cylinder ends the same way to make our doughnut (technical term is “torus”), which is flat for the same reason the cylinder is.
In practice, though, even if the universe is closed, you could never travel far enough to see where you came from. The speed at which you could travel is limited to less than the speed of light. The expansion of the universe is faster than that (this is permitted by relativity since nothing is actually moving faster than light). You could never “catch up” to yourself. New space is being created between wherever you are and your original locations at a rate faster than you could travel through it
Yes, there are more now....................
Wrong, wrong, wrong! The apparent expansion of the universe can easily be explained by the fact that the speed of light has a defect and slows down over the vast distances that it travels. Einstein also said that light can be affected by gravity and this was subsequently proven. So it can be affected by the vast gravity of the universe and slow down, thus making things appear to be receding. A much simpler and more correct view of the universe.
Where Is The Center Of The Universe?
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The problem with answering that question is that we live in a reality ruled by relativity. The farther away we look, the faster objects appear to be receding. In such a universe every possible observer would make that same observation. Therefore every point is the center point. Obviously, intrinsically, this can’t be the case, and is merely an effect of relativity.
Except that there is absolutely no evidence that light ever travels at a speed other than c. The “speed of light” is actually a misnomer: yes it is the speed at which photons travel, but it is much more than that. It actually is a fundamental physical constant that governs all kinds of interactions that seemingly would have absolutely nothing to do with light. Things like sizes and brightness of starts, half lives for various radioactive decays and many more phenomena would have much different observed values if light speed actually changed over time, distance, or due to gravity.
The effect of gravity on light is real and Einstein did predict it. But it is not a change in the speed of light. It is a change in direction light travels due to passing through the gravitational field of a massive object. The displacement of stars during a total eclipse was predicted by Einstein and first measured by Arthur Eddington. This was one of the first experimental confirmations of relativity. The phenomenon of gravitational lending, where multiple “copies” of a distant object are observed if light passes near a closer massive object is another manifestation of the same effect. However it has nothing to do with the speed of light changing. It would be extremely easy to detect such a change in light speed if it did happen. No evidence for such a change has ever been observed.
I seem to remember reading somewhere long ago that they located the site of the Big Bang and it was somewhere in the direction of the constellation Sagittarius.............
That depends on what you mean by “collide”. At a fundamental level, all ordinary objects contain much more empty space than a galaxy does. Almost all of the mass of your car, for example is confined to a volume that is a minuscule fraction of what you would regard as the volume of your car. Almost all of that mass is in the nuclei of the atoms making up your car. There is very little outside the nuclei. The odds of two atomic nuclei occupying the same space at the same time in a car collision are minuscule - at least as low as two stars occupying the same space at the same time in a galactic collision. Yet, the car collision invariably has great affect due to the forces in play. The same would hold true (in terms of the large-scale structures) in a galactic collision.
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