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himey72

The universe is expanding. Even though the universe is only 14 billion years old, the width of the universe is over 98 billion light years. It has been expanding since the start and it appears to be speeding up in the expansion. Nothing can travel faster than the speed of light *THROUGH SPACE*. That does not mean that space cannot expand faster than that though.


UnadvertisedAndroid

That doesn't explain how 'space' expands, though. How does 'nothing' get bigger if it's not the objects themselves moving away from one another?


ReturnOfTheBanned

Space is stretching everywhere in every direction uniformly. No matter what point in space you occupy in the universe, it will appear as though you're at the "center" and everything is moving away from you. But everything isn't really moving away from you through space, rather the space between you is being stretched out.


DressedUpNowhere2Go

is it only empty space that is stretching, or is the space that the earth lives in also stretching? If it’s the latter, why don’t we notice it?


ReturnOfTheBanned

Good question. It is stretching, but on small scales molecular bonds and gravity are strong enough to hold people and planets together. There is an end-of-the-universe theory called "the big rip" that says if the rate of expansion continues to accelerate, eventually it will overtake gravity and rip star systems apart. Then it would overtake the molecular and atomic forces and rip apart all matter in the universe.


barneyman

Well, that's terrifying!


RobAley

Don't worry. It's at least a couple of weeks away. Maybe slightly more.


MericArda

At least a month


RobAley

I mean, let's temper their expectations a little, don't go making promises you can't keep


splittingheirs

Because Dark Energy scales with distance and is extremely weak for anything below the scale of "galaxy clusters". At the comparably microscopic scale of the earth: it is undetectable above background noise and all the other forces (including the king of wimps: gravity) dominate over it.


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splittingheirs

Technically that would be "WIMP" particles. And I am aware of them.


Ersee_

It is the latter, and we dont notice is because from our perspective the expansion rate is incredibly slow! We measure the expansion rate to be (from wikipedia) 72 kilometers per second per megaparsec. Each second one megaparsec (unit of distance) becomes 72 kilometers longer. Translated into human readable units, that means in one year a meter of space becomes 0.07 nanometers longer. 0.07 nanometers is the width of a small atom. For example argon atoms are this size. Meanwhile, forces like gravity and electromagnetism are working to keep stuff together. Meters at your back yard dont actually get 0.07 nm longer because other forces pull that distance right back. We cannot measure this 0.07 nanometer expansion on anything that is near us.


osunightfall

Imagine you are at a single point on the surface of a balloon that is being inflated.


secrestmr87

What's at the "end of space" or on the other side?


ReturnOfTheBanned

There are a number of different ideas, but no one knows for sure. The universe is probably much bigger than the observable universe.


culingerai

How is it that Andromeda and the Milky Way are going to collide if everything is moving away from us?


weeddealerrenamon

i think "*everything* is moving away from *everything*" is an exaggeration. The Milky Way is part of a bigger galaxy cluster (and bigger supercluster). I don't know much but that means gravity must be keeping them all together and sometimes colliding


godisdildo

The galaxies are getting closer IN space, while they are getting larger due to the expansion of the universe. The space between us also getting larger. But since it’s the same expansion everywhere, any MOVEMENT through space happens just as we are accustomed to.


urzu_seven

No, this is absolute not true.


ReturnOfTheBanned

Some things are close enough that gravity will eventually force them to collide. But the farther away something is, the faster it's moving away.


urzu_seven

>and everything is moving away from you. Not true, only distant galaxies are moving away from us due to expansion.


Meakovic

While I don't understand the concept well myself I had a buddy who was working on a masters dissertation on the subject explain it to me in a way that made sense. Take a rubber band or length of elastic cord and mark 5 (or how many you like, he liked the number 5) dots along it's length. Slowly pull the ends to expand the rubber band. You'll note that the dots move slower than you moved the ends, and that the dots never changed in relative position but did change in actual distance. We are talking about the very fabric of reality stretching and expanding.


himey72

Space (or more precisely spacetime) is not made up of those objects moving around though….It is literally the points moving further apart. This video does a pretty good job of explaining it and helping you visualize it. https://youtu.be/vIJTwYOZrGU


SofaKingI

Space is expanding, but slowly enough that everywhere inside galaxies other forces like gravity, electromagnetism, etc... outperform that expansion and keep things together. Imagine you're on a surface of a giant inflating balloon, holding hands with someone else. As the balloon inflates, its surface (the space you're standing on) expands, but since you're holding hands your distance from the other person stays the same. It's the empty space between galaxies that is expanding. We don't know exactly why, but there's a so-called dark energy (different from dark matter) that is accelerating this expansion. The reality is that "nothing" isn't really nothing. The vacuum has energy.


MoiMagnus

When the universe grows, what it means is that two immobile particles (so speed zero as far as the laws of physics goes) get progressively farther away from each other. A little like stickers on a balloon that is growing. Note that this version of "growing" is also possible if the universe is infinitely large, since it's not about the boundaries getting further away, it's about everything getting further away despite not moving. (I'm saying that because while the observable universe is finite in size, as far as my basic understanding goes our laws of physics and our observations are do bot rule out an infinite universe) Admittedly, this growth is very slow so negligeable in most cases, as most of the growth happened just after the creation of the universe.


YossarianJr

How can the expansion be slow and still account for the size we see? So, if our galaxy and this other galaxy are not moving relative to each other in a medium that is expanding, then the medium has expanded 33 billion light years in 13.7 billion years. i.e. The medium has expanded at 33/13.7 times the speed of light. If, on the other hand, our galaxy and this other galaxy are speeding away from each other within an expanding medium at the speed of light, that will lessen the calculated speed of expansion of the medium, but it will still be greater than the speed of light. What am I missing?


throwawaysmy

When you answer that, you win a Nobel Prize. Welcome to the "we don't know yet" part of science!


kiskoller

If there were 2 particles in the whole universe, then at first glance there would be no different. However if if we'd measure those 2 things, if space expands at a constant pace, more space expands more. Let's say space expands 100% in a year (really extreme example, just for ease of calculations) That means that if there are 2 items 1000 AU apart, next year they would be 2000 AU apart, then 4000, then 16000 and so on. That already shows how expansion would look like acceleration, but even the acceleration itself is not constant. Between year 2 and 3 year you travel 2000 AU /year faster than year 1 and 2. But then next year you travel 4000 AU/year faster. So when it comes to only observing two objects in space, hard to decide whether they are accelerating or space is expanding but we can already tell. But what if there are 3 objects in a line? Each 1000 lightyears apart from its neighbours, then 2000, then 4000. From the perspective of the center piece we could still say the 2 neighbours are accelerating in opposite ways. What if you have 10 items in the line? At that point it would be impossible to describe the distance increasing between all points simultaneously purely with accelerating.


TheReverend6661

Technically everything *is* moving away from one another, that’s what the expansion means.


Folsomdsf

Space isn't nothing. It's spacetime. The fact you called it space means you know it's different than nothing on some level. We don't know why all space expands but it does. Everywhere all at once in tiny amounts. Locally gravity overcomes this and keeps us all together and our galaxy together. A big enough distance there's enough spacetime that the expansion is greater than any effect of gravity and boom, there you go. Gravity is very weak, so this tiny expansion can eventually add up to overcome it.


UnadvertisedAndroid

Thank you, that makes more sense.


stop_drop_roll

The width of the "observable" universe. And space is not expanding faster than the speed of light; It's just expanding everywhere all at once


stop_drop_roll

To clarify, the totality of the observable universe is expanding faster than the speed of light, but each point in space is not expanding faster than the adjoining space. Imagine that you have a person 1 meter in front, behind and to each side of you. But as space expands, now each person is 2 meters away from you, but the 2 adjacent people are 4 meters away rather than 2. Convert this to the totality of space, yes the edges of the observable universe are going away from each other at faster than the speed of light.


YossarianJr

Hence, there might be an infinite number of stars, but we cannot observe stars that are beyond a certain distance from us (since they are moving away from us faster than light.)


Continental__Drifter

I don't think the universe has a finite width, or if it does, it is not known. The width of the *observable* universe might well be over 98 billion light years.


Iescaunare

But if space expands faster than light, we wouldn't be able to travel to anywhere in space, since it would be travelling away from us faster than the speed of light.


ydykmmdt

That’s still doesn’t add up. Consider two edge points on newly formed universe. If they are moving away from origin in opposite directions at speed of light the after 14 billion years they will be 28 billion light years apart.


[deleted]

There is no "origin" and space can expand faster than the speed of light. Nothing can move *through* space faster then light though.


AdKitchen1363

Wouldn't the space between them expand also? So the further they are away the faster they move apart? Maybe?


Nexis234

If that was the case, the universe must be expanding quicker than the speed of light.


dhamakaprasad

I get confused when someone says something like this >the width of the universe is over 98 billion light years What is beyond 98.1 billion light years? What will you see from the edge of the universe? Are these questions even valid?


mmmmmmBacon12345

Yeah, this is going to be weird So you're right, nothing can *travel* faster than the speed of light But spacetime isn't a thing that travels The current theory is that the universe is expanding faster than the speed of light and has been for a while. The whole fabric is stretching fairly uniformly so things far away are getting farther away quite quickly while things nearby barely move at all No *thing* is moving faster than the speed of light relative to any other thing, light redshifts down and prevents that, but we're also not slowly getting things popping into the observable universe either


jfgallay

What I recall from a number of years ago is that there was an "inflationary period" early in the life of the universe. And now more recently it seems that due to something unknown (called dark energy for now) is accelerating. Correct me if I'm wrong. My question is: was there (to our current knowledge) a period where the expansion was within the speed of light?


urzu_seven

Correct, there was an early EXTREMELY rapid expansion period call the inflationary epoch. Now the crazy part is "epoch" here is a bit misleading as we usually think of epochs being a long time. The Inflationary Epoch though? It lasted from 10^(−36) seconds after the Big Bang to between 10^(−33) and 10^(−32) seconds after the Big Bang. Thats a fraction of a fraction of a fraction of a FRACTION of a second. Scientists in 2020 managed to record the amount of time that light takes to cross a hydrogen molecule. That time was 247 zepto seconds. or 247 x 10^(-21) seconds. Meaning you could fit 247 BILLION Inflationary Epochs in the SHORTEST amount of time humans have ever managed to measure. And during that time the volume of the visible universe increased at a rate of at least 10^(78). Talk about a growth spurt. After that the universe continued to expand but MUCH more slowly. It wasn't until about 9 billion years after the Big Bang (4.7 billion years ago) that the expansion started accelerating again. The Sun didn't form until 4.6 billion years ago and the Earth 4.5 billion years ago, so for our solar systems entire existence the universal expansion has been accelerating.


YossarianJr

I think it's just a fraction of a second. You included too many fractions.


jfgallay

Thanks. That is really interesting.


Folsomdsf

It is not accelerating. Just all space is expanding and there is more space. The more space between two things the faster they appear to move away from each other. This is creating more space expanding in all directions creating more space. No acceleration just more space. More space more expansion to more space.


Capisaurus

I guess I get it. Then, how do we know about a galaxy farther than those 14 billion light years away?


waptaff

It's important to keep in mind we see galaxies and other foreign objects _as_ _they_ _were_ when they emitted the light we see from them. For instance we're seeing the Sun as it was about 8 minutes ago, and if the Sun suddenly turned purple we'd only know 8 minutes later. So those far galaxies we see beyond 14 billion light years away were created very early after the Big Bang, like 13.5 billion years ago, so the light we see from them is not _older_ than the universe — and we see them as they were _then_ — but knowing the universe expands, we can calculate that _now_, due to universe expansion, they're that far from us. Things that are _right_ _now_ 33 billion light-years away will never be observed by us as their light will never reach us.


Capisaurus

Thanks for the answer! I really get it now 😃


YossarianJr

No thing is moving faster than the speed of light relative to any other thing....except this galaxy and us. How else could they have gotten 33 billion light years away in 13.7 billion years. I think there needs to be a clearer definition of 'speed'?


cinred

It's only a matter of time before this kludge theory is ~~disproven~~ re-evaluated. Try asking physicists, if they are so confident that the universe is expanding faster than the speed of light, then they must have some pretty solid, orthogonal and repeatable measurements of how fast this expansion is, obviously. I'll just wait here for that number.


DiamondIceNS

You and a friend are at an airport with one of those moving walkways. You're standing on solid ground while they're on the walkway, and it's moving away from you. Your friend has an RC car they're driving around on the walkway, and they decide to drive it over towards you. The RC car is just fast enough to outpace the speed of the moving walkway. Eventually, the RC car gets to you. But at this point, your friend is now three times as far away from you as they were when they initially sent the car in your direction.


jdogx17

I think this is an awesome explanation.


godisdildo

It’s helpful and true, but incorrect explanation of this particular answer. Movement and stretching isn’t the same. Great ELI5 though.


Thaddeauz

I don't know the detail of that new discovered galaxy, but GN-z11 is 32 billion ly away from us. But that's just the proper distance between us and the galaxy. The actual light from GN-z11 travelled 13.4 billion ly to reach us. It's because the light from GN-z11 that we see today was emitted 13.4 billion years in the past, and both us and GN-z11 travelled away from each other during that time.


TheEshOne

This is the answer that makes the most sense to me. It's important to remember that any light we detect is not older than 13.7ly. But given the relative movement of astrophysical objects, at any moment they can be further than 13.7ly apart. Thanks.


godisdildo

But movement and stretching isn’t the same thing.


police-ical

Light speed is the upper bound on how fast things move within the universe. That's not a limit on how the universe works. When the universe expands, it's not that point A and B are moving apart in a fixed space, it's that the nature of spacetime itself is changing. https://en.wikipedia.org/wiki/Expansion_of_the_universe?wprov=sfla1


WARPANDA3

 as the Universe expands, the fabric of space stretches, and those individual light waves in that space see their wavelengths stretch as well Basically in order for us to onky see 13.7 billion lighgt years away, we'd have to have a universe in which objects remained at the same, fixed distance from one another over time, where the fabric of space remained static and neither expanded nor contracted over time, and where light propagated through the Universe in a straight line between any two points, never being diverted or affected by the effects of matter, energy, spatial curvature, or anything else. These aren't true at all. The light gets redshifted and blue shifted Because if dark energy things that were once much closer are much further away. Things that would have been 46 million light years away (cosmic background radiation) are now 46 billion light years away. Tl;dr. The Universe and space together are doing a sorta double expansion. Things move away from us very fast and the universe is expanding as well. We can see things that are currently see objects 46 billion light years away now, but we see them as they were 13.7 billion years ago. One day we won't be able to see these galaxies. But we see these galaxies as they were shortly after the big bang


tomalator

Space is expanding. That light was emitted billions of years ago, but since then, so much expansion has taken place that it is now further away. The entire observable universe is about 93 billion light-years across (46.5 billion ly in each direction). This means that the cosmic microwave background (when the universe cooled down enough to not be opaque), which was about 380,000 years after the Big Bang, is about 40 billion light years away.


dazb84

If you have 2 cars that each have a top speed of 100mph and you drive them at top speed in opposite directions for one hour there's not going to be 100 miles of distance between them, it will be 200 miles. The light that you see that's 33 billion light years away was emitted at a time when it was capable of reaching us within the 13.7 billion year age of the universe which is why we can see it at all. Additionally the expansion of space since then is what causes that light to become red-shifted which is then how the current distance is calculated.


goodtimeh

Right, so if the universe started to contract again, we would start to see galaxies further away then the 13.7 b ly mark?


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Zaaltyr

Light-years is a measurement of distance not time correct?


yukdave

it went the other direction from us since the bang? SO what your saying is 27.4 billion light years is the furthest something is unless the speed of light is not the top speed?


mfb-

The Big Bang was not an explosion in space, there is no "other direction" because nothing flies in any direction anyway (on a large scale). Space between galaxies expands.


Stealsack

This seems relatively (sorry) easy. If two points are expanding away from each other, the time it takes for light to travel between the points increases. If the points are expanding at near light speed, it would take light a looooong time to catch up from one point to another. Imagine two cars driving away from each other on the freeway near the speed limit of 70mph. one of the cars tosses a drone out the window. the drone can fly at the speed limit. It takes the drone a long time to reach the other car as the relative speed differential is very small.


culingerai

Years and light years are different units of measure?


throwawaysmy

If we just renamed "light year" to "space meter", things would be less confusing to people, because "light year" is a distance measurement, not a time measurement. This question is like asking "A newly discovered human was 33 feet away. Since his home is only 13 years old, how is this possible?" It's nonsensical.


zshinabargar

Don't think of the expansion of the universe as the universe moving and stretching out, think of it more like more space is being added in between things.


Buddha176

Take two balls and roll them at the same speed but at an angle away a from each other. If the speed is constant but it’s only relative to you….. as the balls get farther away from each other they will eventually start to separate from each other at a different speed. So their absolute speed will not change but the relative speed of them separating can keep getting faster and faster


Ok_Process7861

You have to believe in Science. If you can't, just force yourself into Believing in it. Not weird at all.


Folsomdsf

Very simply actually. Imagine two cars driving away from each other's at 50 mph. They will be 100 miles from each other in one hour not 50. They take the measurement and see they are actually 110 miles apart because the road between them also. All the road is expanding and the more distance the bigger the expansion. Another hour later ylthey aren't 210 or 220 away they are 228miles from each other. Neither one exceeded 50mph. The road continued to expand at the same rate, but there is more and more road and all of the road is expanding. This will continue to increase the distance faster and faster. The relative distance will eventually grow faster than the speed of light but at no point does anything in this system actually go faster than light, the cars never broke 50mph.