/sci/ - Science & Math

>>3536673
That is one possibility. There might also have been time in the traditional sense before the big bang.

>>3536690
yes, I understand that...however, please address the request.

I forgot to put a question mark. I'm a dummy.

>>3536695
It's a pretty simple concept. There was nothing, and then there was something. Voila, start of time.

Originally, everything was super compressed into a singularity. All matter, time, laws of physics, were compressed into said singularity. Then it started expanding extremely rapidly.

>>3536709
False. Or at least, not yet confirmed. The evidence is out on that.

>>3536699
I understand that there are random occurrences of atoms coming into existence out of nothing (random chaos quantum physics stuff), but how can there be nothing before the big bang? There has to be something to trigger it, or a place for it to come into existence, and if that's so, there has to be a time before it, no? I just can't see nothing, not even time, existing before existence. It's as if I expected a drawing (or image) to form on a piece of paper without touching it. I'm not implying there was a creator, but there had to be something before the bang, no?

I'm straying off though, I just want to understand the concept. If there was nothing and no time before the big bang, what caused the big bang?

static singularity
Nothing changes, no way to measure time, no way to apply the measurement of time, time has no effect, time has no cause, no time, no need, the end... and then suddenly the beginning.

>>3536709
let's say that is the case, then if that singularity exists, it's occupying some form of space and existing in some form of time, no?

>>3536727
>here has to be something to trigger it, or a place for it to come into existence
Why?

>>3536673
Ever heard about big crusch teorum its says its kinda recycle procces of universe.. Couse not all universe is expanding some will be pulled together again to couse a new big bang.. Dont think that i,m troling its only a theory but its concept is based on that gravity works over really huge distancies

>>3536735
that's the part I'm having a hard time accepting. If this universe sprang out of nothing and started everything, then wouldn't it be at least a little bit logical to assume it happens more than once? Shouldn't we be experiencing universes within our universe that just spring out of nothing?

I guess that I just don't want to accept that a universe can spring out of nothing.

>>3536743
Ever hear that became highly implausible given the new evidence of the last 20~ years?

>>3536750
>I guess that I just don't want to accept that a universe can spring out of nothing.
I don't mean to sound condescending, but, that's nice.

>>3536761
I'm not sure if it's a matter of me not wanting to or just having a hard time comprehending it. Like I can imagine how big or solar system is, but I can't fully comprehend how far each planet really is or how big they are in relation to each other...does that make sense?

>>3536727
>what caused the big bang?
yeah well, now that's a logical problem, even if there is such and answer, let's call it bigger bang, you could still ask for what caused the bigger bang and so on, ad nauseam, so even though you can ask for what caused the big bang it doesn't mean that the question has any meaning whatsoever

"Whereof one cannot speak, thereof one must be silent."

>>3536756
Dude.. Not all universe is expanding thats a fact.. U would be impressed over wich distancies gravity works. When you work with the new equations

>>3536783
Then go publish it in a physics journal instead of 4chan, and I might take you seriously.

I don't think time is something that we as humans can fully grasp. The extent of our understanding of time is that the longer time goes on, the older something gets. After that, I believe there is no more we can say about it, unless we find evidence pointing to a certain conclusion. We are just like the inhabitants of flatland, but instead of being unable to grasp height, we are unable to grasp time.

Though I'm not sure if they have found evidence to say that there was NO time before the big bang, I have yet to see "Curiosity". If someone can link me to a torrent or a direct download that would be greatly appreciated.

>>3536783

gravity works over any and all distances since distance is one of the variables needed to calculate gravity

>>3536769
I'm not asking what caused the big bang or what existed before it as much as I am how can a universe and time come into existence out of nothing? How can there not be a time before time? That there's no first moment of time...

Would it make sense to say that if there was a big crunch before the big bang, the instant in which it went from crunching to banging, everything was contained within a single point, everything approached zero mass, zero space, zero time, before it flipped to expand, but at this exact moment before expanding it was zero, and being zero could not be measured, so progress could not be measured, and therefore was zero and infinite. Lasting no time and forever.
Is this reasonable?

What about if instead of a "before" time, or a time previous to this singularity, a "negative" time, instead negative is folded back to the positive time side and exists simultaneously and parallel with the timeline we are in.

>>3536787
It is published in book... You should really read more...
Read about pioneer anomaly.. I dont remember other articals at the given time but there is many

>>3536792
>We are just like the inhabitants of flatland, but instead of being unable to grasp height, we are unable to grasp time.
Pretty much this. Monkey brains can't visualize such an image.

>>3536821
>pioneer anomaly
Oh boy here we go. In the off chance you're not trolling, that alone does just prove that gravity "changes" over long distances. It's more likely that there's been a minor glitch on the spacecraft, or that we're not modeling it accurately enough.

>>3536821

You seem to have an excellent grasp of written communication and I see no reason to doubt your choice in literature, which you can not even cite or link to.

>>3536828
I'm assuming now that you think of time as of 4th dimension.
You know, many people can perfectly visualize it, but that doesn't make any difference.

>>3536801

>How can there not be a time before time?
here you talk about what existed before the big bang, even though you claim
>I'm not asking [...] what existed before
so, question dismissed

>how can a universe and time come into existence out of nothing?
well, don't let that keep you from sleeping, if that's what the evidence says then let it be and be glad that we know a little more about our universe than before

>>3536819
so what would that imply? Some form of mobius strip scenario?

op, it's a figure of speech.

the more mass something has, the greater it's gravitational field is.
the greater its gravitational field, the more time slows down as you approach the field.

thus, if the entirety of the mass of the universe were once contained within one supermassive object, time around that object would have been so slow that as a rate it would be practically zero.

...or something.

why does time slow down as we approach something supermassive? i have no fucking clue. i'm just a layperson who is absolutely confounded by physics on microscopic and macroscopic scales.

>>3536835
You bastard its hard to copy paste from ipad :D
http://en.wikipedia.org/wiki/Big_Crunch
http://en.wikipedia.org/wiki/Pioneer_anomaly

>>3536850
http://physicsworld.com/cws/article/news/41740

>Gravity’s effect on time confirmed
>The researchers exploited wave-particle duality and superposition within an atom interferometer to prove that an effect known as gravitational redshift – the slowing down of time near a massive body – holds true to a precision of seven parts in a billion.
>Gravitational redshift follows on from the equivalence principle that underlies general relativity. The equivalence principle states that the local effects of gravity are the same as those of being in an accelerated frame of reference. So the downward force felt by someone in a lift could be equally due to an upward acceleration of the lift or to gravity. Pulses of light sent upwards from a clock on the lift floor will be Doppler shifted, or redshifted, when the lift is accelerating upwards, meaning that this clock will appear to tick more slowly when its flashes are compared at the ceiling of the lift to another clock. Because there is no way to tell gravity and acceleration apart, the same will hold true in a gravitational field; in other words the greater the gravitational pull experienced by a clock, or the closer it is to a massive body, the more slowly it will tick.

...but is time slowing down or do things just appear to move slower?

>Confirmation of this effect supports the idea that gravity is a manifestation of space–time curvature because the flow of time is no longer constant throughout the universe but varies according to the distribution of massive bodies.

trying to comprehend all this makes me not want to exist anymore...

>>3536862
>using wikipedia as source
oh god

>>3536878
Meh. It's not that bad for the level of sophistication of /sci/.

>>3536878

>Uses no source for his void assertion

Oh dear.

>>3536878
Do you wish me to copy paste my books?

>>3536881

>Pretentiousness overwhelming

Oh Allah.

part 1

OP,

isaac newton was one of the first to put out the idea of defining "space." as in, the area in which things can exist. he postulated the idea of space being exactly the sense that one would normally define it as. newton put forth the idea that space is what all things are relative to. that is to say, when you spin around, you're spinning around relative to the absolute space around you; you are not spinning the world beneath your feet (that would mean things are moving relative to you!). but where does time fit in to all of this?

newton's idea of an absolute space lasted until einstein came along with general relativity. general relativity in tldr form basically says: everything is relative, there is no "absolute space" which newton put forth. instead, all points of view are correct (relative to one another). think of it like this: if you were to go jump off of your house into your pool, you aren't falling into the earth--you stay perfectly still and the earth comes up to catch you. still, where does time fit into this?

>>3536878
>mfw I see no problem using wikipedia as a source
provided it is outside of the scientific realm, of course

>>3536883
yeah, good luck quoting wikipedia on your dissertation

>>3536885
name them, let's see what you got

I heard a guy with a beard created the universe

>>3536896

yeah, maxwell

>>3536889
>think of it like this: if you were to go jump off of your house into your pool, you aren't falling into the earth--you stay perfectly still and the earth comes up to catch you
wait..wut?

>>3536904
In General Relativity, "at rest" means at rest in an inertial frame. If you are accelerating, then you are not at rest. Gravity is not a force in this model; it is a bending of space time. When you "fall" towards the Earth, you are "at rest". When you are sitting in the chair, you have a force exerted on you by the chair accelerating you at about 10 m / s^2 upward.

>>3536889
So... many... things... wrong...

part 2

time comes into play when you begin to play around with the idea of how gravity affects clocks. if you and i both had precise, accurate atomic clocks, and you stayed on a mountain for 10 years, and i stayed in the valley for 10 years, would the clocks read the same time at the end of the experiment? nope! they'd be different! not by much, but it'd be there alright. so now we can begin to see that gravity has an effect on time. this is when einstein started to realize that space and time were very closely related. you can't affect one without affecting the other. pic related, it explains what i just said; it's gravity warping the spacetime around it.

here's where i finally answer your question. you asked "how can there be no time before the big bang?" well... because space as we know it did not exist. therefore time (as we know it) didn't exist either. so here's your next question: "what caused there to be spacetime?" nobody really knows. quantum mechanics says there is no such thing as unoccupied space, so something had to exist beforehand. there's a few nobel prizes and few blowjobs from the pope to be given to the person who figures out the answer to that question.

hth

Our invisible bodies- james alfred
The general principles of reality A- robert l. Demelo
Physics of the imposible- michio kaku

The last books comes trough some questions that relates to given questions here other books are to good to find awnsers u need

>>3536915
>this is when einstein started to realize that space and time were very closely related
That's not how it happened. At all...

>>3536910
I'm a dummy so bear with me: how can you be at rest when falling if you're accelerating at the speed of gravity? I slept through physics if that's not apparent.

>>3536920
You're not accelerating when you're falling. Everything else is accelerating up. No really. That's how one describes it in the model of General Relativity.

>>3536925
I don't understand this. I would appreciate it if you could explain it to me, simply if you can.

>>3536916

I take it as you read 1 and 3, and cite 2 because you want to claim actual knowledge on the subject, bring real scientific papers, not kaku pop-science

>>3536931
Why do you think that you're accelerating when you're falling? Because it looks like everything else is staying still. According to the model of GR, actually everything is accelerating upwards, while you falling are actually at rest in an inertial frame.

>>3536937
Fuck of dude. The guy just stated shit load of scientific reasons, and you are just being ignorant

>>3536938
in my puny brain it seems to me like you're implying that I'm at the center of the universe and it moves around me...


Is this me at rest based on my perception?

>>3536910
>In General Relativity, "at rest" means at rest in an inertial frame.
but intertia is never zero because of gravity...
>If you are accelerating, then you are not at rest. >Gravity is not a force in this model; it is a bending of space time.
this abstraction is confusing. why did einstein create this model?
>When you "fall" towards the Earth, you are "at rest".
because there is nothing impeding you from falling toward the earth.
>When you are sitting in the chair, you have a force exerted on you by the chair accelerating you at about 10 m / s^2 upward.
ok... so gravity wants to pull mass toward mass. however, things with mass take up space. there is a force at play here and that force is what is being described as the upward accelleration. that force is what is keeping us as distinct entities rather than condensing into a single mass... or something...

so einstein's model of general relativity is an attempt to describe the movement of space and time.

>>3536945
No. If you're sitting in a chair, then you are not at rest in an inertial frame. You are accelerating (upwards). Only in free fall are you at rest (in an inertial frame).

>>3536938
Thats actually completely wrong.
It ignores space time. Either how have always been at rest or you are acceleration

>>3536948
>this abstraction is confusing. why did einstein create this model?
In some sense, he didn't "create" it. One might say that this all was already known. Lorentz transforms and such. Einstein was the first to look at the equations and say "You know, what if these were actually legit in the logical extremes, like this space-time nonsense?". Thus GR.

Alternatively? Why did he do it? Because it's the simplest way he know how to formalize the model and accurately describe the real world.

>>3536931
it's not something you're going to get in a matter of minutes. the easiest way to think about it (to me) is to imagine as you're falling, you stay perfectly still, and the earth just follows its normal path. just let the thought fester for a little while. go outside and look around. ask questions about how things are moving. like:

when you stand still, are you entirely still?
no, because you're moving with the earth.
is the earth still?
no, it's moving around the sun.
is the sun still?
no, it's swinging around an arm of the milky way.
is the milky way still?
[just guess]

so what /is/ "still"? when you begin to ask, "well, what is motion then?" you're getting there.

>>3536952
I don't know what you're saying.

Also, this is basic GR. You are at rest in and only in free fall. Sitting in a chair is not free fall.

>>3536945

yes to every single point in the universe, it is the center of the universe

>>3536949
what do you mean by inertial frame? I guess that's throwing me off.

I don't understand how sitting in a chair is accelerating me. I understand it's fighting the force of gravity.

>>3536962
No its a simplification of gr that ignores the warping of reality.

>>3536966
As I say again, in the model of GR, gravity is not a force. You feel .. something .. in the chair because the chair is pushing against you. If you held an accelerometer in your hand, it would tell you that you are accelerating upwards at roughly 10 m / s^2.

>>3536949
so basically, gravity is being... isolated... so we can look at the other forces.

when we observe that nothing is impeding movement adherant to gravity, then there is zero acceleration because there are no other forces to consider. if something impedes gravity, that something then becomes a force.

hmm. actually that kind of makes sense if we're trying to isolate forces.

i'm repeating myself but i'm barely understanding this. like... is gravity considered a constant in the general relativity model?

jesus, i know fuck all about modern physics.

also, fuck the captcha. i just failed it for a record 5 times in a row.

>>3536960
alright...let me see if I get this

if I'm falling, there's nothing pushing or pulling me thus nothing accelerating me. Everything else IS moving though; Earth around Sun, the Sun through the galaxy, the galaxy through the universe... So if gravity is not a force, Earth will eventually "accelerate" towards me? Is that sort of it?

>>3536984
In GR, gravity is not a constant nor force. Instead, the worldline, the line in 4d that represents your future "at rest", your worldline, happens to intersect with the chair's worldline and the Earth's worldline. Gravity warps spacetime so that worldlines are no longer Euclidean.

This is also the model of how gravity affects light, which has no (rest) mass. Light follows a straight line. Gravity bends space time so that two parallel straight lines can actually intersect, aka be not Euclidean.

>>3536993
When the Earth and the Sun go around their shared center of mass, they are in free fall. A body in orbit is in free fall. There are no forces acting on it.

>>3536971
In the simplified model which ignores space time. It has nothing to do with what you feel.
You cant feel gravity. You feel the opposing force.

>>3537003
brah, you lost me.

Where's Carl Sagan when I need him?

Ignore gravity for a moment. Suppose there are no forces on an object. Then plot its position versus time. You will get a straight line, since its velocity is constant. If we think of time as a fourth dimension, we can say that inertial motion is making a straight line in spacetime.

Now consider what happens when we try to draw straight lines on a curved surface, for example a sphere. On a sphere, the shortest path between two points, and therefore the closest thing to a straight line, is to move along a great circle, a circle that splits the sphere into two equal halves.

In ordinary geometry, lines that start out parallel stay parallel forever. But on the sphere, any two great circles eventually converge and cross. Think of two longitude lines as an example.

The path in spacetime you make while falling and the path the center of the earth makes are straight lines in spacetime, but as you move along the lines, going forward in time, they converge, causing you to hit the earth. That's because the geometry of spacetime has curvature, much like the sphere does.

>>3537007
I think I just said that.

>>3537010
Dunno. I've done about the best I can. Maybe try wiki?

>>3537015
so how does this explain that when I jump into a pool, I'm at rest and the pool is accelerating towards me?

>>3537025
I appreciate the info, though

Wish I would have paid attention in class...

>>3537027
The pool is being pushed upward by the earth.

Imagine you wrapped a ribbon around a globe. The center of the ribbon can make a great circle, but the sides of the ribbon do not. If the sides did follow great circles, they would intersect the center of the ribbon. But they can't, because the width of the ribbon is fixed.

>mfw I saw this gif and I thought this is /sp/ and already had half of wall of text about how suddenly /sp/ is trying to be smart written

>>3537049

I don't see how one is related to the other.

Am I being really dumb about this or is there a clearer example?

>>3537059
great circle = geodesic (closest thing to straight line in a curved geometry)
freely falling = geodesic

not moving in a great circle = not a geodesic
accelerating = not a geodesic

>>3537071
Got it. Now, how does that translate into the pool accelerating up towards me while I'm falling at rest...

There's always been something that somewhat answered my questions about time and God, even our universe. The Omniverse. To think that there could be other dimensions and literal universes that don't follow our laws of nature, time itself might not even be a concept. Hell, our universe might've descended from a similar one.

>>3536916

so which one has the earth shattering new equations for gravity that allows it to work for even greater distances than any and all distance?

is this pool thing like if I'm on an elevator going up, I can say I'm either feeling the force of gravity pulling me down or the elevator lifting me up, but since we're disregarding gravity, it's the lift accelerating me up? I swear, I've never felt so stupid in my life
>graduated relatively high in my class in HS
>graduated from a pretty prestigious college

So much misinformation.
OP, You see how time is made by people and can't be considered a dimension, neither we can accept concept of being no time or some other kind of time before the big bang?

>>3537090
Did you just take universe, name it differently, and then demote the classic universe to mean just our spacetime, and not everything?

>if you were to go jump off of your house into your pool, you aren't falling into the earth--you stay perfectly still and the earth comes up to catch you

ok, my last attempt to understand this: Since I'm the observer, and I'm jumping into the pool, relative to me, the pool is coming at me as I jump off the roof. So say I was the pool and someone was jumping into me, relative to me, the person is coming at me, and I'm not accelerating towards them...? yes?

>>3537085
If the pool wasn't accelerating, the distance between it and the center of the earth would shrink at an ever-increasing rate until it reached the center. Just like two great circles converging on a sphere or someone in freefall near the earth. But that obviously can't happen because the ground is in the way. The ground under the pool gets squashed a little bit, causing it to exert an upward force on the pool that makes the pool accelerate upward.

>>3537134
No. Whether something is accelerating or in freefall is absolute. It's not relative. The pool is accelerating; you while falling are not. It doesn't matter from whose perspective you look at it.

>>3537138
this doesn't make any sense to me. I swear I'm not trolling, I appreciate you trying to explain it to me.

>>3537144
I don't get how if I'm falling and moving (my understanding accelerating towards the earth at 32ft/s2) I'm at rest and the earth is accelerating towards me...

>>3537147
Do you understand that there is a force under the pool from whatever is supporting it, pushing up on it? It's that force that causes the pool to accelerate upward.

simple, at 1st there was nothing, but even nothing is something. therefor bang. something exists.
and it only seems like it went really fast because there was nothing around at that point with a comprehension of now and then.
till there was one, it would've all went instantly.

>>3537164
When you say accelerate upward, what do you mean? Because from my perspective, it's not moving.

>mfw this thread reminds me of the fact that my entire family consists of christians that are too shallow to understand the concept of moving atoms and all the time they go like 'silly atheist (they don't see difference between agnostic and atheist), everything was created out of nothing, yes? you so silly'

>>3537128
Well, is it that farfetched to think that even our universe is part of something larger?

>>3537158
Let's completely ignore the pool and put you far enough above the earth's surface that you can't even see the pool, but you're still falling.

Start with no gravity, but you and the earth are still converging. The distance between you and the earth is shrinking. You can equally well say that the earth is moving and you are at rest, or that you are moving and the earth is at rest. Either description is correct. But in neither description is either you or the earth accelerating. Does this stuff, without the trickiness of gravity, make sense?

Okay, now we put in gravity. Neither you nor the earth accelerate; you're both in freefall. The distance between you and the earth is again shrinking, which wasn't a problem before. The reason you might think that you or the earth is accelerating is because the distance is shrinking at an increasing rate.

But that just comes from inappropriately trying to apply the rules of geometry you're familiar with to the space between you and the earth. Say a pilot starts at the equator and flies north along the 10E latitude line. The distance between him and the prime meridian shrinks at an increasing rate. So if he was a flat earther, he might conclude that either he is curving toward the prime meridian, or the prime meridian is curving toward him. But that would be wrong. But the pilot and the prime meridian are following the closest thing to a straight line possible in that geometry.

ITT /sci/entists (ie, highschoolers) can't understand dumbed down as fuck explanations given in plain english

>>3537183
You are falling toward the pool, correct? From your perspective, it starts out at rest, and moves upward toward you at an increasing rate. The pool is close enough to you that it is an excellent approximation to apply the old-fashioned rules of geometry. Therefore it is valid to conclude that either you or the pool is accelerating. The correct conclusion is that the pool is accelerating.

>>3537224
>But in neither description is either you or the earth accelerating. Does this stuff, without the trickiness of gravity, make sense?

you lost me here

Time just means change of state. If the singularity came into existence from a quantum field of potential fluctuations then time existed before the big bang. The big bang theory doesn't say there cannot be change of state before the big bang, only change of state within the actual singularity that inflated to become the universe as we know it.

inb4 some creationist crap about how atheists think everything exploded for no reason.

>>3537232
The correct conclusion is that the pool is accelerating.
why?

>>3537197
As I understand it, universe means EVERYTHING. When you find something new, it becomes part of the universe. Thus it would be redundant to say universe is part of something bigger because at that moment, "that something bigger" has become part of universe, i.e. everything.

See what I mean?

>>3537232
I should add that the first sentence
>You are falling toward the pool, correct?
is just how you would ordinarily describe the scenario, not what is actually going on. In your reference frame, you are motionless. There are other inertial reference frames in which you are moving at a constant velocity, but none in which you are accelerating toward the pool. The ordinary description is using a non-inertial reference frame -- the perspective of an observer not in free fall. But it's the free faller's perspective we're interested in for the purpose of physics. Free-falling perspectives -- inertial frames -- are special.

>>3537242
There is a force on the pool. There is no force on you; you are in free fall.

>>3537236
>Start with no gravity, but you and the earth are still converging. The distance between you and the earth is shrinking. You can equally well say that the earth is moving and you are at rest, or that you are moving and the earth is at rest. Either description is correct.

So this part you are okay with?

Why would you think either you or the earth are accelerating in this scenario? In both descriptions, you/earth is at rest or moving with constant velocity.

Remember this is the scenario where we imagine there is no gravity.

>>3537242
Last post of the night.

If you put an accelerometer near the pool, and kept it there, it would report an acceleration of roughly 10 m / s^2. If you dropped an accelerometer, while it was in free fall, it would report an acceleration of about 0.

>>3537246
Ahh, I get what you mean, but I'm viewing it more like we would view the galaxies.

>>3537158
>I don't get how if I'm falling and moving (my understanding accelerating towards the earth at 32ft/s2)
Imagine you have a reference frame around you. Your center is motionless in it. That 'accelerating' reference frame is inertial. The 'acceleration' is illusory. Get it, dumbfuck?
>the earth is accelerating towards me...
No, the earth is falling, too. It's center is motionless in an inertial reference frame. You and it get SPATIALLY closer until you and it's surface collide: that's electrostatic force causing acceleration. You and the earth continue in a reference frame where your combined center of mass is motionless.

there's no before, since time and space didn't exists before

>>3537237
Thank you for that image.

>>3537256

Alright, I get everything up until the plane example. But still, I don't get how me jumping into the pool = me being at rest and the earth coming up to catch me. Maybe a visual would work better for me. I've never felt so dumb.

>>3537300
As somene stated above. You 're free in the air. The pool has the force (think gravity) and pulls YOU to self.

Forgive me if this sounds retarded, but just for a sake of argument, let's assume I have a twin exactly opposite of me on earth (that is, through the earth via center to the other "side") and he also has a pool to jump to, and we decide to do it at the same time.


....but if earth is not acting upon us with some force (with us of course acting with equal and opposite force on earth) whilst I'm falling to the pool, but the earth is "catching me," then how does my hypothetical twin on the opposite side of earth also manage to end up in the pool?

I feel really dumb for saying this, but if the earth is "catching" me, how can it "catch" some one else at the same time?

>>3537308
Nonono, you imagine the 'pulling you' concept in a bad way.

>>3537305
You're implying that the pull of the earth is making me accelerate towards it, not that I'm at rest and it comes up to catch me
>>3537308
This.

>>3537300
Okay. What's confusing in the plane example?

Do you get that the plane's path and the north half of the prime meridian are both the shortest path from their starting points on the equator to the north pole? That even though the plane maintains its speed, the distance between the paths shrinks at an increasing rate? That on a flat earth, such a thing could not happen if the paths were really optimal?

>>3537330
I understand that. I don't get how that relates to the pool catching me while I'm at rest.

>>3537308
The problem is that you're now trying to apply the familiar rules of geometry to a region large enough that they no longer apply. In curved spacetime, the fact that two objects start out at rest with respect to each other and then the distance between them starts shrinking does not imply that either one accelerated.

>>3537347
But the distance is not merely shrinking, it's shrinking exponentially. How is that not acceleration?

>>3537337
Well, first let me emphasize again that the weird thing isn't the pool catching you while you're at rest; that can happen even without gravity. The weird thing is that you started out at rest with respect to the earth, and without accelerating, managed to hit it.

You have to do this using time as a dimension. The path in spacetime of an object in freefall is a geodesic -- the closest thing to a straight line in spacetime. The path in spacetime of an object that's accelerating is curved. And objects at rest with respect to each other have parallel paths in spacetime. Does this make sense? Try drawing some distance vs. time plots if you don't see it all right away.


The globe example demonstrates how two geodesics can start out parallel to each other, and still meet. Just like the spacetime paths of the falling person and the center of the earth.

>>3537366
By "exponentially," I assume you mean at an increasing rate.

That is the flat-geometry notion of what acceleration is. It doesn't apply in curved spacetime. Under the new rules, acceleration means that the spacetime path of the object is curved; it deviates from a geodesic.

>>3536801

It's kind of like measuring the distance a tree travels during it's life.

It doesn't move so there is nothing to measure.

Only here the distance is time and the tree is matter. How do you measure time when there is nothing to age.

>>3537377
it seems to me that you're explaining two different things. I get the two geodesic paths that start out parallel can meet. But I'm still failing to understand how if I jump off my roof into my pool, I'm at rest and the earth is accelerating towards me. I don't see how that relates to the geodesic lines. In my head, the earth is at rest and I'm accelerating towards it due to gravity.

>>3536889

if it's not asking to much, if you draw it out, I'm pretty sure it'll all click.

>>3537401
>But I'm still failing to understand how if I jump off my roof into my pool, I'm at rest and the earth is accelerating towards me.

Again, the point is not that you are at rest. At rest or moving is relative. The point is that you are not accelerating.

Not accelerating means that your path in spacetime is a geodesic.

The earth's center is not accelerating either. Let's ignore the pool and the ground -- that's just complications -- and pretend you could fall through the earth like a neutrino. The earth's center's path and your path meet, even though both paths were geodesics. Just like those paths on the globe.

>>3537423
Alright. I think I understand that. However, I still don't understand the example in this post
>>3536889
maybe their wording is wrong or I'm getting hung up on semantics...

>>3537420
Okay, here's a picture. Here your path in spacetime in spacetime looks curved, but that's only because the geometry of the computer screen is flat, so the image is distorted. The same would happen if you tried to draw longitude lines on it. Both paths in spacetime are straight.

>>3537439
I totally understand that. I guess where I got stuck was that in this post:
>>3536889
>think of it like this: if you were to go jump off of your house into your pool, you aren't falling into the earth--you stay perfectly still and the earth comes up to catch you.
he was saying that one way to look at it is this way, and I took it as that's the only way to look at it while you could also look at it as the earth stays still and you fall into it... or am I still being the biggest idiot to ever post on 4chan?

>>3537439
So, it's not that me or earth is going faster, but that space is shorter?

>>3537430
Well, that post isn't entirely correct. It says that any point of view is just as good as any other, but that's not true. It's correct to say that the pool is accelerating and the falling person isn't. The post would imply that the pool's perspective that you are accelerating is just as valid. But if you and the pool both have an accelerometer, the accelerometer will measure that it is the pool that is accelerating.

What it is possible to do is work in a coordinate system in which the pool's position coordinates stay constant. But that's just a mathematical description. The question of who is accelerating is something that can be resolved with physical measurements.

>>3537456
in free fall you're weightless and while the pool is feeling the effects of it pushing against earth...or somewhere along those lines?

>>3537455
That's a reasonable way to picture it.

>>3537462
Yes.

>>3537471
took forever but I got it. Thanks for the help

>>3537467
I knew that spacetime had this property, but trying to understand it here just blew my mind. Where should I look to learn more?

I must get better handle on this.

>>3537494
If you want to get into the details, you'll need to learn some calculus up to the point where you can understand what a differential equation means (if you haven't already), and the 4-dimensional formulation of special relativity (if you haven't already), maybe read about tensors a bit, and then look for a general relativity textbook.

>>3537523
In to the rabbit hole it is.

Thanks for help, quite rare to find people on 4chan who are patient enough to actually help others understand something.

And stuff on general relativity isn't hard to find. Simply googling the phrase turns up good hits:

http://math.ucr.edu/home/baez/gr/
http://www.youtube.com/watch?v=hbmf0bB38h0
http://www.amazon.com/General-Relativity-Robert-M-Wald/dp/0226870332

going back to op, what do you guys think would happen if we could go back in time 13.70000000000000000001 billion years?