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Shadowkiller00 t1_j1ghfnn wrote

There are several problems with your statement.

First, 46 billion light years is referencing the size of the OBSERVABLE universe. Not the size of the entire universe.

Second, it's 46.5 billion light years in radius. So that's 93 billion light years across.

Third, the universe is constantly expanding. The universe is 13.5 billion years old and yet 46.5 billion light years of light has reached us. So in the 93 billion light years you spent trying to cross the currently observable universe, it would expand to 300 billion light years or more. In other words, the observable universe is expanding faster than light speed and you would basically never reach the other side traveling at light speed.


AnnonBayBridge t1_j1gjb6q wrote

Question from non-expert: how is it possible the universe expanded to 40+ billion light years when it’s not even that old? Like did the universe expand faster than the speed of light?


Efficient-Finding-34 t1_j1gk236 wrote

Yes, the universe is expanding faster than the speed of light. This means that there are parts of the universe which we will never see.


TLRsBurnerAccount t1_j1gnrmz wrote

It'll be impossible to see, but I really wonder what the expanding edge of the universe actually looks like


duckiegooseman t1_j1goass wrote

Looks exactly like what you see from earth because it doesn't have an expanding edge, but rather the space between "things" just get bigger, so to an observer sufficiently far away, earth is on the edge of their observable universe


Artikay t1_j1gszt9 wrote

So if you place Earth in the center of our observable universe, and call it Planet A, then you take two planets on the far opposite ends and call them B and C. Does that mean to Planet A, B and C can be seen, but to planets B and C only Planet A can be seen?

Basically B and C have more than one observable universe between them? It would take exponentially longer for light to reach between stars because there is more space to expand between them?

If there is so much space between ends of the universe could two points be so far apart that light could never get from one end to the other?


Wind_14 t1_j1gu400 wrote

the last one is the consequences of observable universe though. Yeah there's a point where light simply can't reach the other side, because the expansion is faster than the speed of light, thus limiting the size of the observable universe (of course, this is assuming our prediction/projection is really true which is the farther an object is from the center the faster the expansion rate is between them and center).

And you don't have to assume that earth is the center of our observable universe, since it is (or rather the center of your observable universe is you).


duckiegooseman t1_j1hf4ic wrote

Yes to the last question. Actually since the universe is accelerating faster than light, every second more and more "things" get so far away they are "lost" to us permanently because light from them can never reach us anymore. At some point far far into the future, our cosmic horizon would be complete emptiness in every direction, and our galaxy would be the only thing that even exists to us anymore.

But to B and C, they don't exist for each other. Information from B can never reach C and vice versa.


TLRsBurnerAccount t1_j1gp27x wrote

I guess what I mean more I wonder what it's like being beyond the edge of the universe and essentially being crested by the edge


420binchicken t1_j1gpqoh wrote

AFAIK that’s not really how it works. For them, they are the centre point at which the universe is expanding from. It’s all relative to your own frame of reference. No solar system is more on the ‘edge’ of the universe than any other.

Please someone correct me if that’s wrong. Space is big and weird.


inventionnerd t1_j1gs85e wrote

This is true if we're going off the belief the universe is infinite. Then yes, everyone can only see in a 46b radius and are therefore at the "center" of their universe.


sbrt t1_j1gtcr9 wrote

It was explained to me that it is the 3d equivalent of a 2d creature living on a globe that is expanding. I can imagine that but I have no idea if it is accurate.


ZincMan t1_j1i1jce wrote

Can we judge our location in relation to the “true” center of the universe ? I mean I assume if the Big Bang was centralized, there must be a “core” to that expansion where everything is expanding radially outward…. But now that I think about it, it still might appear as though everything in relation to you is leaving your observable edge of the universe at equal speed regardless.


inventionnerd t1_j1i2ctp wrote

It wasnt centralized though. Basically the current theory is the universe is/was always infinite and is just a bigger infinite now. The mass might have been far denser and closer together before the space expansion, but it wasnt in like a 1 mm radius sphere or something. It was always in an infinitely sized space.


gtga1976 t1_j1i4b96 wrote

That's space itself though yes? I assume the mass within space shows differential in red shift relative to earth based on some other central point? Or are you saying everything is travelling away from earth at the same speed?


inventionnerd t1_j1i8w3u wrote

Not quite sure what you're saying, but no, everything isn't traveling from Earth at the same speed. But I'm saying wherever you are in space, you'd see the same frequency if you look far enough as you see on Earth? So, our observable universe is about 46b lightyears in radius. To us, we're at the center right? We see a redshift of x when looking straight "up" to the very edge of our universe. If we can teleport to this this spot instantly and look around us, we'd still see a universe of about 46b lightyears in radius (just would be mostly different things as you could see from Earth. If you then looked straight "up" from this spot, you'd still see the same redshift of x as you saw when you looked at your current spot from Earth. So, how could you ever tell what the central point is if everywhere you go, you'd have the same size observable universe and same shifts?


The_Most_Superb t1_j1gu3pk wrote

There is only existence and non existence. Beyond the universe is nothing. Unfathomable nothingness.


Caveman108 t1_j1gwkoj wrote

Except we don’t know that. If you could travel multiple times the speed of light, ideally many multiples, you could reach the edge of the observable universe. There you very well might just find more universe. We don’t know there’s an “edge.” Just an edge of what we can see.


museabear t1_j1gpsvz wrote

And what’s on the other side.


Smartguyonline t1_j1h3xg2 wrote

There is no “other side” of the universe or “before” the Big Bang. Those concepts don’t make any sense.


DWright_5 t1_j1guykl wrote

Why isn’t the speed of light the speed limit?


woodlark14 t1_j1hfcgi wrote

The speed of light is how fast an object can move through space, but the universe isn't expanding by motion, it's expanding by changing the size of space. To us an analogy, consider a balloon with objects on its surface. The speed of light is how fast objects can travel across the surface of the balloon, but if the balloon is inflated then the distance between two objects can change faster than that speed.


ZincMan t1_j1i27ci wrote

I understand what you’re saying but I don’t get how the expansion speed and “travel” speed would have different hypothetical limits. If things are expanding, I’m assuming it’s “relative speed” but it is indeed traveling faster than the speed of light relative to something … or rather why does traveling through space have a speed limit at all?


woodlark14 t1_j1i3ljj wrote

From the perspective of relativity, everything is always moving at a constant speed through space-time from every perspective. The faster something is moving through space, the slower it is moving through time and vice versa. Light speed is achieved when an object has no mass, resulting in it travelling entirely through space and experiencing no time passing. There's a whole bunch of effects that result from this like length contraction and time dilation.

Space expansion is very different, It has nothing to do with the object you are observing, it is instead a property of the space between you and the object. In a sense neither object has relative motion, instead the ruler you are using to measure the distance between the two is changing it's length.


ZincMan t1_j1i6t4n wrote

Fucking hell. I don’t even understand your first sentence. However what your 2nd paragraph is saying I think I get. Does expansion not count as moving through space ? I understand expansion speed is relative to the observer, but surely the fastest things could expand away from each other has to be twice the speed of light right ? Like if two objects are “expanding” away from each other at the speed of light in opposite directions… their relative speed to each other would seem as though they are traveling twice the speed of light right ? (Assuming you could observe) I guess my questions is can expansion travel faster than this ? Faster than two objects speeding away from each other at light speed ? I don’t get the difference between travel vs expansion. Is expansion actually Stretching reality itself?


woodlark14 t1_j1iczf1 wrote

Apologies, relativity is quite hard to explain especially without diagrams. The answer to your other questions is that it is reality that is stretching, the distance between two galaxies becomes larger rather than one of the two galaxies moving into a new space. So it's not limited by the speed of light.

As for your questions about the fastest two things can move away from each other, that's actually a more complicated question than you realise. The issue here is that the maximum speed anything can be observed to be moving at is the speed of light. If you took two objects moving away from you at 0.75c (0.75 times the speed of light) then from the perspective of one of those objects the other wouldn't be moving at 1.5c. Instead it would be moving at 0.96c, and you would notice that clocks on the objects no longer match yours.


JasonMontell2501 t1_j1gxmnj wrote

It actually is the speed limit for everything except the universe itself


TripleATeam t1_j1gki0d wrote

Not only what everyone else says, but space seems to expand at a constant value per unit of volume. Thus the more space there is, the faster it expands. Thus eventually (as far as we know rn) we'll stop seeing other galaxies. We'll be alone.


f_d t1_j1gva4w wrote

The Local Group is bound together by gravity. It should stay together as long as the fundamental forces keep working like before. The rest of the universe outside that threshold will keep stretching away endlessly.


TripleATeam t1_j1gvm96 wrote

I thought it was just the galaxy that was bound tightly enough and the local group would eventually go as well? Huh. I guess I learned something.


mavric91 t1_j1gm8kr wrote

A metaphor I’ve always liked is the raisin bread one. In this metaphor, the raisins are galaxies, and the dough/bread is space-time. When you bake the loaf, the dough rises and expands. And once the loaf has finished baking the raisins are now farther apart than when they started. But they aren’t farther apart because they moved through the dough away from each other. They are farther apart because the dough expanded. The substrate they exist in expanded, space between them expanded, and now they are farther apart.

So when we talk about the universe expanding, we aren’t talking about galaxies simply drifting farther away from each other. We are literally talking about space itself expanding. The emptiness itself between galaxies gets bigger. And that process can happen faster than the speed of light.

It’s also worth noting (and I’m not that up to date on this so someone correct me) that the Big Bang isn’t like everything just started expanding from a single point at the speed of light. It’s more like all of a sudden everything just was. Not instantaneously, but in a matter of seconds the early universe just was, and it was big (millions? Billions? of light years big). And from that point it began to rapidly span outwards. And again, the Big Bang wasn’t all of a sudden matter exploded into the empty space-time of our universe. The Big Bang created our universe. It created space. Before it there was nothing. Not nothing like empty intergalactic space nothing. I mean like no-such-thing-as-empty-space nothing.

So yah the universe can expand that much in a short amount of time.


highjinx411 t1_j1gp9bm wrote

Weird. It just makes me crazy thinking about there being nothing and then something for no reason at all.


mavric91 t1_j1gpxnc wrote

Yah the trick that works for me is just to not think about it too hard or else I risk full existential crisis.


starsblink t1_j1h03e5 wrote

I just like to think that we don't know yet. Our universe could be inside a grain of sand on a beach we can't see yet.


f_d t1_j1gwp98 wrote

>It’s also worth noting (and I’m not that up to date on this so someone correct me) that the Big Bang isn’t like everything just started expanding from a single point at the speed of light. It’s more like all of a sudden everything just was. Not instantaneously, but in a matter of seconds the early universe just was, and it was big (millions? Billions? of light years big). And from that point it began to rapidly span outwards.

The idea is that all the energy and space started out packed together densely, then rapidly expanded everywhere at once similar to how space is expanding everywhere at once today. Even when it was packed together densely, it could have been infinitely large. Just denser than it is now.


Ebonicus t1_j1gx706 wrote

I wonder if the space between all quarks is also expanding. Meaning the raisins are getting bigger and we won't notice it, because the ruler is getting bigger too.


e36freak92 t1_j1gk0sj wrote

Yes, there are galaxies moving away from us at faster than the speed of light. The expansion of spacetime itself isn't constrained by special relativity.

Also it's expanding everywhere at once, not just the borders getting father away, which is really hard to wrap your head around


Aldodzb t1_j1gnjqk wrote

So the black background we "see" it's just more universe but we cannot see it because we are getting apart from each other at a speed faster than the light?

Can something move away from us, in a direction, faster than the speed of light and something else in the same direction but opposite way too? It seems odds, where are moving then?


norbertus t1_j1glbyo wrote

> Yes, there are galaxies moving away from us at faster than the speed of light

No, "the speed of light" is a cosmic speed limit. There is no valid mathematical framework for "galaxies moving away from us at faster than the speed of light"

As an inertial body approaches "the speed of light" (which varies by medium, causing, for example, the optical effect of "index of refraction"), the amount of energy required to continue to accelerate that body approaches infinity.


bendvis t1_j1glyal wrote

Right, but all of those rules only apply to objects moving through space. Space itself is also expanding, and taken with the movement of the galaxies through space, distant galaxies are moving away faster than light.

That is, if you fired a laser at one of those galaxies today (and assuming the universe continues to expand forever) the light from the laser would never get there. The distance between the ray of light and the galaxy would continue to grow even though the galaxy isn’t moving through space faster than light.


polovstiandances t1_j1gmpfo wrote

How is it possible? What does galaxies “moving away” actually mean? Isn’t the space expanding at the edges like a droplet of water or something?


bendvis t1_j1gnl3b wrote

The common analogy is an ant crawling across the surface of an inflating balloon toward a specific spot. The spot is stationary on the balloon’s surface and the ant is moving toward the spot, but the distance between them is growing because the size of the balloon is growing.

Compare the expanding 2d surface of the balloon to space itself, and that’s why distant galaxies are moving away. Like the spot, they’re maybe not moving, but the distance between us and them is still growing.


polovstiandances t1_j1gofji wrote

Thanks for your reply. So then how can one explain why the rate at which this expansion process happens isn’t a function of the speed of light at all? If the analogy serves, I can only blow a balloon up as equivalently fast as the speed of light, meaning there’s some max distance that can be produced in some time delta between the ant and the target spot, no?


420binchicken t1_j1gq6pn wrote

No, the speed at which the balloon can inflate, or the universe can expand, is not limited by the speed of light. The speed of light is a speed limit for things moving across that space, not the space itself expanding.


polovstiandances t1_j1gqrop wrote

Ok, well that’s like, fucking insane right? Maybe my understanding of the concept of space needs revision because conceptually I believe space to still be an object, and nothingness to be space, meaning that an “object” is still moving across a plane (of nothingness) at a rate. But this isn’t very physical or scientific I guess


bendvis t1_j1grw9y wrote

Imagine a wave traveling through water. Each water molecule doesn’t really go anywhere. It just gets bumped and jostled by its neighbors and it ends up moving in a circle as the wave passes through.

Light is a wave too. It’s a wave passing through the electromagnetic and mass fields in the same way that a wave passes through water. Light is a vibration that propagates through those fields. So, empty space is an area whose fields aren’t vibrating. The fields are still there just like water is still there when there isn’t a wave passing through it.


polovstiandances t1_j1gs4lm wrote

Oh wow, this was a really helpful image. Thank you. Damn I should have studied this shit.


bendvis t1_j1gpibe wrote

The speed at which you can stretch a balloon’s surface and the speed at which an ant walks across the balloon’s surface are distinct and separate things that aren’t related.

The same is true of the speed at which light (or gravitational waves or information in general) propagates through space and the space it’s propagating through. They’re not related.

Keep in mind that space expanding happens ‘faster’ on bigger scales. If 10 cm of balloon distance expands to 11 cm over the course of a minute, then the points that were 10 cm apart are moving away from each other at 1 cm/minute, even though neither point is moving across the balloon in its own frame of reference. If the balloon were enormous with two points 10 light years apart and it expands at the same rate, they’d be moving apart at 1 light year per minute - much faster than the speed of light.


polovstiandances t1_j1gpzu1 wrote

Ok this makes sense. But still doesn’t touch on how fast spade can expand, and whether there is a max limit to that. But I guess you’re saying that yeah, space still cannot expand faster than a certain rate, it’s just that the rate it expands informs a different understanding on the time plane. But space cannot expand faster than the speed of light, right? What I mean is just the raw rate at which the universe is expanding must be some function of an expansion rate even if it causes the amount of total space to exceed the distance achievable by the speed of light, right?


bendvis t1_j1gqo13 wrote

According to one theory, during a time called Inflation, space expanded really fast. The volume of space expanded 10^78 times larger in 10^-32 seconds. That was way faster than the speed of light. This super rapid expansion explains why the cosmic background radiation is so nearly perfectly even - because at that time in the early universe, it was all in one point. If there is a limit, it would have to be faster than that.


polovstiandances t1_j1gqx97 wrote

That’s fucking nuts. I need to know more. Thanks.


bendvis t1_j1gs98d wrote

My wife and I just discovered a really well done YouTube channel called Astrum. Their video on black holes is fascinating and covers this stuff in a clear and straightforward way. Highly recommended!


f_d t1_j1gysd5 wrote

>This super rapid expansion explains why the cosmic background radiation is so nearly perfectly even - because at that time in the early universe, it was all in one point.

It wasn't necessarily in one point, it was just extremely dense and homogeneous. Space could have been infinite even when everything was packed together tightly.


East-Dot1065 t1_j1gofq8 wrote

Another analogy I've seen used you can do yourself.

Place your hands flat on a table with your fingers together and the tips of your thumbs touching. Keep your thumbs touching and move your hands apart while spreading your fingers slowly. No one finger tip will be moving faster than the next, but the tips of your pinky fingers will be moving away from each other much faster than anything else. That's because distance between them is growing no matter their movement.


polovstiandances t1_j1gojw0 wrote

Thanks for the reply. Check my other comment too, I’m very curious.


norbertus t1_j1gmtwa wrote

The speed of light represents a limit for how fast local interactions can be propagated in space-time, or, how quickly an inertial body can traverse a reference frame.

Einstein's relativity is still within the classical Newtonian framework governed by locality, causality, and determinism, but Einstein's major insight was that Newtonian "absolute space" does not exist.

In relativity, it does not matter if space is expanding when we are trying to reason about things like how fast a distance can be traversed. In relativity, speeds are not additive and subtractive the way speed works in the grade school math problem about two boats on a river.

Einstein formulated general relativity in the wake of a major failed experiment, probably the most important failed experiment of the last 150 years.

The Michelson-Morley experiment was trying to measure the speed of light relative to the rotation of the earth by measuring its differential at a given point on the earth rotating either into or away from light streaming out from the sun

It turns out there is no difference in the measurable speed of light, which paved the way for relativity.

As it turns out, relativity is what makes GPS work

And 1905 was the magic year Einstein invented relativity and quantum mechanics (by defining "the quanta")

edit: typo


bendvis t1_j1go9t0 wrote

I mean… I appreciate the long-winded explanation of how light moves through space, but none of it covers how space itself expands and how that can make distant objects move away from us at faster than light.

Again, the galaxies are not moving through space faster than light, but the distance between us and them is growing faster than light-speed because of the expansion of space.

They are effectively moving away faster than light. If you magically took off toward one today at light speed, you’d never reach it.


norbertus t1_j1gojn0 wrote

>long-winded explanation

A joke on the "Aether wind?"

> but the distance between us and them is growing

Missed that, you're quite right there, space itself is expanding.


belugwhal t1_j1gpwkb wrote

>As it turns out, relativity is what makes GPS work

Err...I think you mean relativity must be taken into account for GPS to work. If relativity wasn't a thing, GPS would still work (it would just be easier).


norbertus t1_j1gr1b7 wrote

>relativity must be taken into account for GPS to work. If relativity wasn't a thing, GPS would still work

That statement is logically inconsistent.

The paper I cited above

describes the role of relativistic "time dilation" in the functioning of the GPS coordinate system

relative speed and the relative strength of a gravitational field each affect the local measurement of "time."

In the case of a GPS satellite, which is out in space and farther from us (its users -- and the earth as a gravitational well) and moving faster relative to us (because they need to stay in orbit and constantly fall over the horizon while we are stationary on the ground), these relativistic effects work at cross-purposes.

GPS uses not triangulation to determine a location, but tri-lateration with a fourth satellite to account for timing delays due to relativity.

The paper I cited notes " If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day"


belugwhal t1_j1gtk7j wrote

Umm.. what I said agrees with this. Dude... You wrote all that for nothing. Maybe reread my comment.


norbertus t1_j1guq14 wrote

> You wrote all that for nothing

Also I love to write, and all this is practice



RedMistStingray t1_j1gr3vv wrote

This is easy to conceptualize. If the universe started from a singularity and expanded in all directions, at the speed of light 13 billion years in one direction and 13 billion years in the other direction, that is at least 26 billion light years across. But space is expanding faster than the speed of light, not to mention ALL space is expanding everywhere. It's easy to see why the observable universe is 40+ billion light years across.

A better question would be, do we have any idea how large the entire universe is, including what we can't see? We must be able to calculate how much of the universe we can't see.


Baskin5000 t1_j1gjvra wrote

It’s not this simple, but:

Imagine you stretch your arms out to the side and each arm grows one foot every 1 year. After one year you’ve grown 2 feet of arm length. The universe is like that but more complicated


BigCommieMachine t1_j1gvjyf wrote

My understanding is It isn’t so much that it is expanding faster than the speed of light, but rather that the speed of light changes as the universe expands.

For 99% of the universe, we mostly understand things. On the 1% fringes, we pretty much have no idea and literally probably can’t have any understanding of what the fuck is going on.


Shadowkiller00 t1_j1h6fz6 wrote

Nope. I've never heard anything about the speed of light changing. If it did, it would cause all sorts of havoc with the science.

The universe is expanding. No two nearby points are expanding faster than the speed of light, but when you look at two distant points, the combined expansion been them is overall faster than the speed of light.


jazzofusion t1_j1gofb0 wrote

Can you explain to a physics/science limited person how we know the universe is 13,5 billion yrs old? What existed before this time and how was matter created?


Shadowkiller00 t1_j1gqxc2 wrote

It's... complicated. I'm not sure I fully understand myself so trying to explain it to another person is probably beyond me. But I'll see what I can tell you.

First, light doesn't change in speed, it changes in wavelength when emitted from something moving relative to you (away from you or towards you). It's kind of like the doppler effect where a sound moving towards you will have one pitch, but when it passes you and starts moving away, the pitch changes. Light is kind of the same.

So light emitted from a source moving towards you turns blue and light emitted from a source moving away from you turns red. The faster the thing is moving towards you or away from you, the more the color of the light changes in that direction.

When we look out much beyond our galaxy, everything we see is red, so everything is moving away from us. We can see the things that are furthest away are redder than the things that are near so the furthest stuff is moving away faster than the closest stuff. And by measuring this "red shift" in color, we can calculate how fast these things are moving away. And by reversing that speed, we can calculate how long it had been since those things were where we are now.

Now I'm not sure if this is exactly how it's done, but logically if you calculate how long it had been since literally everything was all in one spot, that can tell you the age of the universe.

Does that make sense? Kind of like one of those old words problems. A train is moving away from you at 60 mph. It is 45 miles away from you now. How long has it been since the train was at your location?


jazzofusion t1_j1hvh6d wrote

Thanks, appreciate the doppler effect color shift explanation. That really helps.


archlich t1_j1h0slq wrote

We’ve observed distant galaxies moving farther away from us. If we calculate the speed they’re going away from us then we can approximate the beginning of the universe. What happened before that time is unknowable.


frowawayduh t1_j1gq5ve wrote

At the speed of light,time is completely squeezed to nothing. A photon simply exists across all of time.


bradyspace t1_j1gkw6s wrote

Just to add to this, it depends on your reference (relativistic time dilation). For the people actually traveling at the speed of light it will seem significantly shorter. They could theoretically travel to the edge of the universe in 100 years, but to everyone on earth it would seem to take them the full 93 billion (not factoring in the expansion)


picaohm t1_j1gokwp wrote

What is the universe expanding into? Or is there nothing there which in turn would actually be something?


Shadowkiller00 t1_j1grlc9 wrote

We can't see the "edge" of the universe. So we have no idea. We don't even know if there is an edge.

Pretend the universe is a balloon. While it's deflated, using a marker, draw two dots on the balloon an inch apart. Now blow the balloon up. As you blow, the balloon is expanding. The two dots will get further and further apart. And yet they haven't actually moved.

Is there really an edge to the balloon? It's hard to say. In a way, the balloon is a two dimensional surface with no clear edge. But only when you look at it in 3 dimensions can you say there is an inside, an outside, and the balloon itself.

Well if the universe is a 3 dimensional balloon, there might not be an edge on 3D space, but if you were to look at the universe in 4D, there might be an inside, an outside, and the universe itself.


tiregroove t1_j1grzc8 wrote

And how do you even know when you reach the end of the universe? Is there an electrified fence or something? Or a bubble membrane you'd bounce off?


splittingheirs t1_j1gz3h0 wrote

Space and Time itself are intrinsic properties of our universe. That is: they do not exist outside of it, they are a part of it, entirely. The universe doesn't expand into anything, it simply creates more space between things.


xl_RENEG4DE_lx t1_j1gsv58 wrote

Not to mention potty breaks and stopping for directions and such


serifsanss t1_j1gszgb wrote

Also because of time dilation for you as the traveler you’d make the trip almost instantaneously. Meanwhile 300billion years on earth would go by


crazzz t1_j1gv7tf wrote

How do you measure that if it’s faster than the speed of light


Shadowkiller00 t1_j1h7dqr wrote

You are not measuring it directly you are observing certain things, like the rate that other galaxies are moving away from us, and using the red shift observed to calculate the speed is moving away, and then you extrapolate based on how far away things are from us that they must be moving away that much faster.


dontmakelemonad3 t1_j1gxnrt wrote

>you would basically never reach the other side traveling at light speed

I'm neither a mathematician nor a physicist, but I don't think that's entirely correct. Although the observable universe would be expanding, it would be expanding both in front of you and behind you. This would mean that regardless of how slow your going, the proportion of distance you cover would be constantly increasing, and you would inevitably be able to get to the other side.


Shadowkiller00 t1_j1h7oyw wrote

That is technically correct. There's a YouTube video about it by... minutephysics, I think, that points it out. But practically speaking, if you said you wanted to travel across the 93 billion light year universe at the speed of light, ignoring other aspects of special relativity, it would take far longer than 93 billion years.


dontmakelemonad3 t1_j1l4130 wrote

Gotcha. When you said "basically never" I thought you were describing some kind of behavior of constantly approaching but never crossing. To me, if we're already talking about a length of time as comically large as 93 billion years, then contextually I would consider no finite length of time to be "basically never," even if we're talking about an amount of time tens or hundreds of orders of magnitude greater than 93 billion.


AllahBlessRussia t1_j1h7kj9 wrote

The space itself is expanding. The road is stretching, not markedly just two cars and the road are moving away from each other, the road itself is stretching. The actual space is stretching while galaxies move away


Mr_SkeletaI t1_j1h7u84 wrote

I’m a bit confused. You state that this is only the size of the observable universe, but also that we know the age of the universe. How could the universe possibly be larger if we know it’s age and rate of expansion. Wouldn’t we just know it’s size then?


Shadowkiller00 t1_j1h8ul0 wrote

I don't have a good answer for you. I'm not actually a space guru. I've picked up a lot of stuff over the years and I general know what I'm talking about, but I don't have the deep knowledge that was required to figure this stuff out in the first place.

What I can say is that we can calculate a lot more than we can observe. So, logically, you are right. But I honestly have no idea of we can calculate the size we think it is. I also can say that, even if we could calculate it, it's effectively a meaningless value because we could never verify it.


BigCommieMachine t1_j1gv6ok wrote

To be fair, there is no real distinction between the observable universe and the whole universe. Saying there is a difference seems to say that there is a universe outside the universe.


Shadowkiller00 t1_j1h76dk wrote

No. That isn't what that means. If you can't see beyond the horizon, it doesn't mean a new world starts at the horizon, the world just continues. If you can't see stars beyond this galaxy, it doesn't mean another galaxy would have to start where we can no longer see. The observable universe is just the region of space that light had had enough time to reach us in, it doesn't mean that is the edge of reality.


akaSyphon t1_j1gka0j wrote

that’s just a guess based on ur guess on how causality works. not a theory, not a educated guess. u can’t jus guess how causality works an act like its a theory and certainly true.