/sci/ - Science & Math

it's just expanding.

basically.

you see, its like being an ant on a balloon. when you fill a balloon with water, it gets heavy and movements made on its surface tend to cause more ripple effect to other parts of the balloon, decreasing the stability of any ants that might be on the surface.

the universe is just like that balloon.

if you still cant fallow, imagine a fruitcake in an oven, with raisins that are an initial distance apart from one another. as the cake bakes and the dough rises, the raisins start to get a little burnt and their edges become less defined as the juices are leeched out by humidity differentials. the analogy of course is that raisins are just like galaxies, slowly leeching their juices to the surrounding bread (voids), and the universe is like the cake, slowly increasing in heat until it is delicious.

it should all make sense now

How does space-time relate to the expanding universe? If the universe expands all that it can and space begins to shrink does that mean time will start going in reverse? And is there any way we could perceive such an effect? Time could be reversing or space could be shrinking at this moment and we may be totally unable to perceive this in any measurable way.

>>5967572

wow man have you read the pages on space-time or did you come up with that yourself?

that's exactly how it works!

reverse time dilation is a direct result of solving Schrodinger's equation such that the geodesics of space time begin to decrease relative to the actual expansion. it was only apparent to the great physicists after lorentz perfected his transformation theories in the early part of the 20th century, but holy shit at you coming up with it yourself. you should really consider a career in physics.

for more reading check these out:
http://en.wikipedia.org/wiki/Differentiable_manifold
http://en.wikipedia.org/wiki/Momentum_space
http://en.wikipedia.org/wiki/Generalized_coordinates
http://www.tandfonline.com/doi/pdf/10.2991/jnmp.1997.4.3-4.23

ive never thought about it myself but perhaps looking at invariant processes (non-revesable chemical+physical transformation) and analyzing for energy leaks from photon-photon backscattering goeding fluctuations could reveal if time has been reversing on us. its all very thereoteical you should reall look into these concepts.

What's beyond the universe? More universe, but with different physics.

>>5967589
I just saw this thread and it just popped into my head. Thanks for the encouragement but honestly I don't have the proper education for physics. Being bipolar gives me periods of increased creativity. So while I can come up with a good idea every now and again I honestly don't have any clue what half the stuff you said means. Nor do I have any understanding mathematically of why my guess was correct.

>>5967542
The universe is not expanding, only theory on the universe is expanding.

The whole theory is based on reading redshift in light, which could be caused by many things.

inb4 my dick

because it's so big

>>5967562
>>5967572
>>5967589
OP here.

I don't understand. Please in layman terms.

>>5967638

I think the people you quoted were trolling you. The balloon analogy was horribly made. Basically, you can use the surface of a balloon as an analogy for space-time as a surface.

If you blow up a balloon with air, you get a surface of some surface area. If you draw two dots on the surface of that balloon, there is some distance between the dots. If you blow MORE air into the balloon, the dots are now an increased distance from one another, but neither has really moved on the surface of the balloon.

This is analogous to the expansion of the universe. Galaxies appear to be expanding away from every other galaxy irrespective of their relative velocities.

Due to the nature of the universe's topology, it can expand like the balloon without necessarily expanding into anything.

Consider the balloon again. If the balloon had no plug (where you blew the air in) you could walk around the entire circumference by going in a straight line drawn on its surface. If the balloon were big enough, you wouldn't even know locally that there was any curve (the surface of a sphere starts to look like a flat plane if the sphere's radius gets big enough). So you could in essence travel in a straight line and end up back where you started.

The universe's topology is conceptualized to be like the balloon's surface in that it wraps in on itself in some way.

If you claim that the universe is expanding into something, you necessarily have to define a boundary to the universe. But would you say there is a boundary to the 2-D surface of a balloon? The 3-D wrapping of the universe is analogous to the 2-D wrapping of the balloon's surface, and it is possible for the universe to be infinitely expanding yet have no boundary, just like the surface of the balloon.

When that guy talked about cake, he was referring to another analogy, with dough. Same thing, raisins expanding from each other but staying in the same place in the dough.

>>5967572
>>5967589

is just gibberish

>>5967683

also this if you want to read from someone who knows what they are talking about:

http://curious.astro.cornell.edu/question.php?number=274

If the entire universe is expanding then our Earth, our Sun, and our entire solar system is expanding. But if everything is expanding at precisely the same rate then there shouldn't be any way to measure it locally. You can't use a ruler to measure expansion because your ruler is expanding too. (I know that's impractical analogy but work with me)

Now if the rate of the expansion of the universe is not constant, as in the expansion rate is slowing down, then when we look into the distant stars and galaxies they should appear to be expanding in relation to us because when we look at those distant stars and galaxies we are actually seeing what they looked like millions of years ago. From this can we conclude that the expansion rate of the universe is slowing down?

>>5967703

You brought up two separate metrics of expansion. Rate over time and rate as a function of scale.

The observational evidence for the expansion of the universe takes many forms, the most recognizable of which is Redshift. When objects emitting light move away from you, the wavelength of the light increases, shifting the light towards the red part of the spectrum.

Researchers found that objects farther from us appear to move faster away from us (higher redshift) than objects closer to us. In fact, everything not significantly gravitationally bound to the earth appears to be expanding away from us, as if we were the center of expansion. This is evidence supporting the metric expansion of space, and is exactly what a dot on an expanding balloon would see if it could note the location of surrounding dots. From every perspective in the universe, it appears that they are the center of expansion (because space is uniformly expanding).

Gravity is an attractive force that works against expansion, and gravitationally bound objects will eventually condense. This is why expansion is not readily apparent in the size of your ruler, even though galaxies far from us might be expanding away at a rate faster than tens of thousands of kilometers per hour. This is also why we will collide with Andromeda, a nearby galaxy. We are significantly gravitationally bound.

Comparing relative red shifting over time has shown that the rate of expansion of the universe is increasing. It could have equally as possibly have been decreasing, but evidence suggests it's actually increasing.

If the rate holds, light from distant galaxies will eventually redshift to the point where we wont be able to detect them, and the sky will grow dark forever. No evidence will remain of the greater universe, and future societies will have no way to know there ever were any other galaxies but our own.

wiki Metric expansion of space and Redshift

>>5967703

also please watch this,

http://www.youtube.com/watch?v=7ImvlS8PLIo#t=51m00s

this is such a great talk by Lawrence Krauss, but the time I linked is when he talks about the disappearance of galaxies and the end of time.

so amazing

>>5967740

holy shit

>>5967589
Ten out of fucking ten.

>>5967608

He's just spouting nonsense.

>>5967683
I like thinking that we're just in a humongous fucking room.

>>5967730
>>5967740
Th...thanks for that. OP here.
I still have a lot of questions concerning the universe though.

>>5967589

>then the universe is expanding into what?
Hyper space, I'm not joking, it's just expanding into higher dimensional space.

I can picture the balloon perfectly on myhead, its expansion, the dots, how every observational point seems to be the center of expansion. What I can't understand, is what's outside the balloon.

>>5969695
Exactly, I imagine a barrier of just nothing. Sadly it is impossible to actually think of what nothing looks like.

>>5969695

From a linked article

"If the universe is indeed infinite, then the simple answer to the original question is that the universe doesn't have anything to expand into. Thinking about infinity is always complicated, but a good analogy can be made with simple math. Imagine you have a list of numbers: 1,2,3,etc., all the way up to infinity. Then you multiply every number in this list by 2, so that you now have 2,4,6,etc., all the way up to infinity. The distance between adjacent number in your list has "stretched" (it is now 2 instead of 1), but can you really say that the total extent of all your numbers has "expanded"? You started off with numbers that went up to infinity, and you finished with numbers that went up to infinity. So the total size is the same! If these numbers represent the distances between galaxies in an infinite universe, then it is a good analogy for why the universe does not necessarily expand even though it stretches."

We are not in the balloon, we are on the surface of the balloon. The surface of the balloon is the 2-D topological equivalent of our universe's 3-D surface. To conceptualize that 3-D surface, you need to look up manifolds. As the above post alludes to, it is possible for the universe to be infinite, ever-expanding, and without boundary at the same time. There is no boundary, much like there is no boundary to the surface of the idealized balloon. The surface of the balloon is a sphere; if you travel on any circumference line of the sphere long enough, you will end up back where you began. If you exist on the 2-D plane of the sphere (as a 2-D lifeform), you would have no traversable boundary through which you could leave the surface.

A few things I feel compelled to clarify, as an astrophysicist:

1) The presently most popular model is that the universe is topologically flat to within ~.4% (i.e. k~0)
2) The universe's rate of expansion of accelerating. Given the ratio of Matter to Dark/Vacuum (roughly 30:70) the rate of expansion was decelerating at a time in the past but it is now accelerating. We know this by plugging these "observed" values (among others) into the Friedmann Equations.

As to what the universe is expanding into... nothing really says it needs to be expanding into anything/something

>>5969822
Topologically flat *(the error in the measurements from which this result came being .4%)*

I wasn't too clear there sorry.
But yes if the universe in infinitely flat then by definition there is nothing "outside" the universe.

What if there is a (or more) layer like this outside of which the galaxies remain where they are but instead the layer distorts the light (by refraction, reflection or gravity) in such a way it looks like the galaxies are moving away from each other.
Galaxies need not necessarily stay at the same place, they may actually be collapsing into each other

>>5969822

I've yet to even take astronomy 101 so forgive my likely ignorant/entry level question.

In its infancy, was the universe expanding at a slower rate? Is there something to account for a gradual increase in the rate of expansion?

By that I mean, what law of physics is responsible for the change?

>>5969697
nothing couldn't exist is there's something around it

"what is the universe expanding into?" is a nonsensical question because the universe is everything and can't expand into something else because there isn't anything else.

>>5969861

It's really not possible. We can watch comets and asteroids enter and leave our solar system and they behave just as they should. We can see nearby galaxies and stars and they behave just as they should. On every progressive scale, the observations add up. It would have to be some kind of super layer that exactly followed the earth, as it rotated the sun as the solar system revolves around the milky way center. It would have to mimic the exact phenomena of light returning to earth from near earth objects while simultaneously distorting the light form galaxies so that they redshift.

Once it becomes so magical, you might as well ask, is it possible for there to be a giant ultra high resolution spherical television screen surrounding the earth, just making us think there is a universe to look at.

here's a question. you're on a closed surface.

where's the center.

>>5969744
>We are not in the balloon, we are on the surface of the balloon. The surface of the balloon is the 2-D topological equivalent of our universe's 3-D surface.
>To conceptualize that 3-D surface, you need to look up manifolds. As the above post alludes to, it is possible for the universe to be infinite, ever-expanding, and without boundary at the same time.
>There is no boundary, much like there is no boundary to the surface of the idealized balloon. The surface of the balloon is a sphere; if you travel on any circumference line of the sphere long enough, you will end up back where you began.
>If you exist on the 2-D plane of the sphere (as a 2-D lifeform), you would have no traversable boundary through which you could leave the surface.

My mind is going to explode!!!
Please explain in layman terms.

>>5971945
A surface with no edge has no center.

is the universe a condom?

OMG LOL

>>5967572
>time goes back and forth forever
>i will forever live this shitty life for all eternity

>>5969865
Hey no problem. I'll answer your second question first. The simple answer is that because the amount of matter in the universe is fixed whereas dark (vacuum) energy is present in all space, the further away things get, the less effective gravity is and the more dark energy accounts for the overall density of the universe.

Here is a graph that will help answer your first question (to which the answer is not a uniform yes or no). Our universe is the top-most curve (with Ωm~.3 and ΩΛ~.7) and the slope of that curve is the rate of acceleration of expansion

>>5972145
gah I misspoke... the concavity represents the acceleration. The slope is the velocity. My bad

>>5972006
This was my exact reaction.

>>5967542
Imagine a balloon inflating. What is the surface of the balloon expanding into? Nothing. The SURFACE isn't expanding into anything. Sure it's moving into a 3rd dimension outside of the 2D surface, but imagine if it where an infinite sheet of rubber that was stretching out. It would no longer be bent into a 3rd dimension. It isn't expanding into anything, but it is nonetheless expanding. Do you understand?

>>5972199
I still have some question is some areas.

Like why is the universe flat?
Is it flat like paper? They say it is flat as in infinite. What does that mean?

>>5972215

I'm struggling with this myself, but basically, imagine if you could shoot a super powered laser beam to a distant galaxy. Then imagine that the distant galaxy shoots a similar beam to a third party, and that third party shoots a third beam back to us.

You would have a cosmic scale triangle.

Now, for a flat universe, if you were to measure the 3 interior angles formed by this triangle, they would add up to 180 degrees.

If we lived in a spherical universe (2-D equivalent is a sphere like the surface of the earth), the we would find that the triangle's angles add up to MORE than 180 degrees. Note the attached figure, where longitude and latitude lines meet at 90 degree angles but two longitudinal lines still converge (parallel lines converging? it can happen outside of euclidean geometry). The triangle in the figure is 90+90+50 > 180 degrees.

If we lived in a hyperbolic universe, the angles would up to LESS than 180 degrees.

The shape of the universe refers to the local and global geometry of space time. Locally on scales of the earth, the universe appears flat, as all our triangles are apparently euclidean. Testing has shown that the universe is most likely flat. Different universe shapes tell us different stories about the evolution of the universe, and whether it can expand forever, or will eventually collapse.

>>5967542
Space and time is expanding. Hence why time passes.

>>5967683

>If you claim that the universe is expanding into something, you necessarily have to define a boundary to the universe. But would you say there is a boundary to the 2-D surface of a balloon?

But what about what's outside that balloon, what the balloon is inlfating in? Like here on earth you would call it air.

>>5972286

Remember that for 2-D beings who live in/on the surface of the balloon, the third dimension does not exist. A 2-D being that was lifted from the 2-D surface of the balloon would have its insides fall out, and all that would remain being held would be the outer tissue layer.

We are not actually talking about a literal balloon, and the analogy does not deal with the balloon as a physical object. We are talking about the topological surface that is similar to the expanding membrane of the balloon in order to explain expansion through dots.

The balloon you are visualizing is also finite in extent, while the universe is understood to be infinite. Again, if the universe is infinite, it can expand while not expanding into anything. There are arguments above and explanations of this fact, and may seem confusing because of the concept of infinity.

I know what you want to consider. If you had a 2-D universe in the form of a flat plane, you could in a 3-D oververse stack the 2-D universes on top of each other, and the 2-D universes would have no way of knowing that other 2-D universes exist, even though in the 3-D oververse many 2-D universes could be seen at one time. (imagine having a stack of papers for example - 2-D planes in 3-D).

There is no evidence for a 4-D oververse where our 3-D universe can expand and be infinite, yet have a fourth dimension in which to move.

The 3-D universe doesn't need a 4th dimension to expand, just as the 2-D universe doesn't need a 3rd dimension to expand.

Because we live in a demonstrably flat universe, the 2-D analog would be an infinite plane, and you can understand that you don't need a 3-D universe to contain a 2-D plane, as there is no third dimensional component.

Because the surfaces are infinite, there is no boundary in a 3-D/2-D universe, and therefore there is nothing but the universe in our plane of existence, and there is no current evidence of (nor need for) additional spatial dimensions.

>>5972311

Furthermore, I don't think you need a 4th dimension for a 3-D universe to be curved either (which our universe is not).

The problem with these analogies is that it makes it seem like spacetime is an actual fabric. Spacetime is a coordinate system; something you can measure. Curves in spacetime and "the shape of the universe" just describe how that coordinate system varies locally and globally.

Almost like a logarithmic scale vs a linear scale (google logarithmic graph). It's just a property of space, and just as you can define a circular buffer in computer code by moving a pointer back to a position, I think you can define spacetime in the same way, allowing for what can be visualized via 2-D analogue as a spherical universe, or saddle shaped.

>>5972332

What the fuck