This is assuming the universe radiated outward from the big bang, so the radius of this sphere would be 13.8 billion light years with its diameter being 2 times that.
Online it says the observable universe is estimated to be 46.5 billion light years wide which doesn’t seem possible.
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The universe is expanding. That doesn’t mean everything’s moving apart. It means distances are increasing. It’s sort of like how time passes more slowly near a black hole, except sideways. Distances are smaller near the beginning of the universe. That light only traveled 13.8 billion light years, but since distances have been expanding, the point it traveled from is now 46.5 billion light years away.
While nothing in the universe can move faster than light, the universe itself is expanding, moving things farther apart.
What’s key here is that there’s how far light can travel, which is one thing. But then there’s how space itself behaves, which is an entirely separate matter. The fabric of space itself is expanding, and the further you get from an observation point, the faster it’s expanding.
Here’s a simple explanation for why the universe seems to expands faster than light speed:
Get a rubber balloon, and draw two sharpie dots next to each other (but not touching), then inflate it. You’ll see as the two dots you drew increase in distance relative to each other. However, did the dots really move? The spots you drew are still technically exactly where you drew them, but the balloon expanding made it look like they moved.
Now, with that in mind, imagine the balloon deflated and the dots moving back and forth from each other. Let’s say that the dots are moving 2cm in a second forward, then 2cm in a second backward, and repeating it forever. When you inflate the balloon, once again the dots start “moving” away from each other. While the balloon is expanding, the dots are still moving 2cm/s in either direction. Here’s the thing: as the balloon inflates, because the dots are already “moving” away from each other due to the expansion, they will LOOK like they’re moving faster than 2cm/s away from each other. If you somehow take a tape measurer and you measure the distance they covered moving away from each other when the balloon was deflated, you’ll see that instead of both moving away from each other 2cm each, they “moved” away from each other at a faster “speed” (even though their personal speed was 2cm/s) and ended up further apart than we expected.
That’s what’s going on with the universe. The speed of light is still the same, but the universe is expanding, so we’re ending up a lot farther away from everything else than we expect. So far all we know is that at some point billions of years ago, the thing furthest away that we could see was 13.8 billion light years away.
EDIT: Although, if you want to delve deeper into it to figure out why it’s expanding, your guess is as good as anyone else’s, including scientists. Here’s some food for thought:
https://www.reddit.com/r/Futurism/comments/1k0gs3w/major_problem_in_physics_could_be_fixed_if_the/
Nobody actually knows, its just scientific speculation based on theories applied to observations.
If the big bang had been an event that happened at a single point location, with all the stuff in the universe starting compressed into a tiny infinitesimal nugget in the midst of empty space, with things then being thrown out from that single point to travel through space at sub-light speed: then yes, the furthest extent of the universe would be an (age of universe × speed of light) radius around the location of the big bang.
However, almost none of that stuff I just said after “If” was accurate. The big bang wasn’t an explosion in the conventional sense (stuff travelling through space away from a central point) but rather a process of space growing larger by inserting new empty space between all the existing points in space. And this happened everywhere in all directions at once.
Any finite volume of current space, traced back towards the big bang, shrinks down towards zero—but the universe at the time of the big bang might still have been infinite. Possibly it just went from an infinity of very densely packed stuff to an infinity of very spread out stuff.
Because the expansion consists of new space appearing in all the gaps, rather than things moving around through space, it’s not subject to a speed limit. Actually it’s not even properly described as having a speed exactly: a speed would have units like “distance per time” (e.g. miles per hour, metres per second, furlongs per fortnight) whereas the rate of expansion uses units of “distance per time per distance“. Because each unit of space grows independently, the total amount of new space appearing in a given gap depends on how many units of space are there already. If every megaparsec of space grows by 70km every second, then two MPc grows by 140km/s and ten MPc grows by 700km/s and so on, until a large enough gap is growing faster than light can cross the divide.
Even if the objects on either side of the gap start out stationary relative to each other and don’t accelerate at all (so you’d think they aren’t moving with any relative speed), new space appearing in between them will cause them to recede into the distance away from each other.
70km per second per megaparsec is approximately the current rate of expansion – in the big bang it was a much higher rate, but still the same structure where the apparent speed, at which an object gets carried further away from you by space, depends on the existing distance.
One part of why the stated radius of today’s observable universe is so extra large, is because it extends out to the current location of objects we can see, even if the light we’re seeing from them was emitted billions of years ago when they were closer to us. The growth of space in the intervening time has inflated the distance. Maybe to a point where light that object emits today won’t actually ever reach us.
Space between galaxies is increasing faster than light, which strangely enough doesn’t violate relativity because no information can be sent faster than light.
So cause and effect is still limited to the speed of light
You forget to take into account inflation, and the fact that its speed is not subject to Einstein’s limits. So while that light was traveling towards us, the space it was going through also stretched.
It’s expanding.
The universe is expanding, which I could rephrase as there’s now more space between things than there used to be. It’s not that the items are moving apart, it’s that space between the items became more space.
Imagine an ant on a 1 ft long string. The ant can cross the string at 1 inch per second, meaning it can cross the string in 12 seconds. But every minute, the ant is taken off the string and moved to another string 2x as long as the previous string. The ant is placed on the point 2x a far down the next string as down the previous string.
So after 1 minute, it’s a 24 inch sting, which the ant can cross in 24 seconds.
Then at 2 minutes it’s a 48 inch string, which the ant can cross in 48 seconds.
Then at 3 minutes, it’s a 96 inch string, which the ant can no longer fully cross before it is moved to the 192 inch string. If the ant is on the right side, it’s now impossible to reach the left side even though earlier traveling from the far right to the far left was easily accomplished.
I could have put 12 ants on the string together and they all would have interacted with each other easily and frequently at the start, but as more time passes and I add more string, all the individual ants are going to end up farther and farther apart from each other until they cannot reach any of the other ants. After an hour there would be ~10^19 inches of string with 12 ants spread evenly across it, even through the ants can only have traveled 3600 inches in one hour.
The comment section isn’t helping the existential crisis.
Imagine you were standing on a giant elastic band. And for some reason you could only walk forward across that elastic band an inch every hour. So an hour walking would put you an inch away from where you started
Now imagine as you were walking I stretched that elastic band out. After an hour i’d stretched it to double it’s length. You were still only walking at 1 in for an hour and you personally only travelled 1 inch, but you would actually be 2 inches away from where you started. That’s because the universe itself expanded.
anything WITHIN the universe (or spacetime as it’s more appropriately called) cannot go faster than the speed of light, but space time itself can expand at faster than the speed of light.
Hope that helps
Spacetime fabric can move faster than light. Everything else, not so much.
Lol, the width is infinite. There is no edge
The universe is under no obligation to be understood. We can use math and astronomy to make observations and models to understand and predict it.
We can make rules and they apply to future science… until they don’t
We can’t even be sure we can know what the universe is. Similar to playing Mario kart. To the player he sees a screen and uses a controller to interact with the game. But that’s not what’s actually going on. There are electrical signals going back and forth. Manipulating electric signals back and forth in the console on the screen and in your body. But we would never win that game.
Universe is inside a black hole I think. From the description of the big bang it sounded like a star going super nova to me… 🤷♂️
Aliens, b!
The theory does not begin from a single point but rather an initial region. Like starting with a glob of cookie dough that expands as it bakes. The starting diameter is greater than zero, therefore the present diameter could be greater than 13.5 billion years.
Or it could be older.
The universe is actually a custom map in a video game where you can design your own maps.
Someone put the size setting on increase and left it sit there, and never bothered to stop it.
Objects within the map aren’t moving, the space between them is.
Imagine a bunch of bacteria in a drop of water. (Universe)
The bacteria can’t move faster than 1 mm/hr. (Speed of light)
Now imagine the droplet hits a surface, and bacteria are carried into a wide area as it spreads. (Big bang)
Three things can be true at once:
The droplet is 5 seconds old
Bacteria can’t move faster than 1 mm/hr
The droplet is larger than 10 mm.
The contradiction comes in because the medium of the universe is itself expanding, which allows for kinda-sorta-technically speeds greater than light, however functionally it doesn’t matter because within the universe all internal laws remain consistent.
Think about two points in a balloon. When you inflate the balloon, the two points move apart but they aren’t moving. This is what more or less is happening with our galaxies.
Many people consider dark energy the force that is expanding the universe and this expansion is accelerating.
So unless that force stops and the universe contracts, at one point you will only see a few surrounding stars and planets.
However, by that time, the sun would have already collapsed into a red star billions of years before engulfing in the process: Mercury, Venus and perhaps the Earth.
There is a theory that theorizes that the information cannot be destroyed. Similar to energy can’t be destroyed, just transformed. Some physics even think that all the information is stored in the boundaries of the universe. A cosmic hologram. So even if we are gone by that time, some information about us might still exist scattered across radiation, entropy and particles or perhaps by that time we are jumping from one singularity to another singularity, from black holes to white holes and from universe to universe 🙂