bendvis t1_j1glyal wrote
Reply to comment by norbertus in Did you know it will still take 46 billion years to cross the universe at the speed of light? 65 mph = 4.8 * 10^17 years! by NotAndroid545
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.
https://plato.stanford.edu/entries/newton-stm/
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.
https://www.onlinemath4all.com/boats-and-streams.html
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
https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment
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
https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html
And 1905 was the magic year Einstein invented relativity and quantum mechanics (by defining "the quanta")
https://en.wikipedia.org/wiki/Annus_mirabilis_papers
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
https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html
describes the role of relativistic "time dilation" in the functioning of the GPS coordinate system
https://en.wikipedia.org/wiki/Time_dilation
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.
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