New Hubble Pictures Reveal Warped View of Galaxies
69 replies, posted
snip
I always enjoyed the Einstein's Cross.
[t]https://upload.wikimedia.org/wikipedia/commons/c/c8/Einstein_cross.jpg[/t]
This is also a really cool gif of gravitational lensing.
[t]https://upload.wikimedia.org/wikipedia/commons/0/03/Black_hole_lensing_web.gif[/t]
[QUOTE=Recurracy;50843725]I always enjoyed the Einstein's Cross.
[t]https://upload.wikimedia.org/wikipedia/commons/c/c8/Einstein_cross.jpg[/t]
This is also a really cool gif of gravitational lensing.
[t]https://upload.wikimedia.org/wikipedia/commons/0/03/Black_hole_lensing_web.gif[/t][/QUOTE]
Holy shit that gif is amazing.
[QUOTE=Jalict;50843765]Holy shit that gif is amazing.[/QUOTE]
For your information that .gif is not actually real. It's just a simulation.
[QUOTE=JohnnyMo1;50810972]
That's why when people ask things like "What would happen if the sun just disappeared right now? Would we know instantly?" the question is really unanswerable. The question breaks the rules of general relativity in the setup.
[/QUOTE]
I thought this is a really valid question. Perhaps not analytically, but wouldn't it be possible to have your initial conditions of space-time curvature to be [I]with[/I] a sun, and then evolving the simulation with no mass at all? Or is it not possible due to certain discontinuities?
I have no clue how GR works in numerical simulations, but I imagine it would be akin to having a fluid with an object as an initial condition and then just evolving the fluid with the object gone.
[QUOTE=Number-41;50843850]I thought this is a really valid question. Perhaps not analytically, but wouldn't it be possible to have your initial conditions of space-time curvature to be [I]with[/I] a sun, and then evolving the simulation with no mass at all? Or is it not possible due to certain discontinuities?
I have no clue how GR works in numerical simulations, but I imagine it would be akin to having a fluid with an object as an initial condition and then just evolving the fluid with the object gone.[/QUOTE]
I'd say where this analogy breaks down is that mass-energy and gravity are more closely intertwined than an object and a fluid. The energy-momentum tensor is conserved which tells you that you can't do it, but it gets even worse. You'll be violating the Einstein field equations. If you have some particular spacetime geometry, you can stick it in to the Einstein field equations and it will tell you what matter-energy content will produce that geometry, but if you let yourself change the energy-momentum tensor arbitrarily without changing the geometry immediately, the left- and right-hand sides don't have to be equal. The Einstein field equations no longer work. So as soon as you say "Okay spacetime is set up like this but now I take this piece of mass-energy out" you're going to be violating Einstein's field equations. I don't think that's a fixable issue, and I doubt you could possibly to call what you're doing GR since you've broken the most fundamental equation of GR.
It would be rather like asking what would happen if quantum mechanics is still true but you knew both the position and momentum of a particle with perfect precision. It's not a "what-if" sort of impossible, you're working with a description of nature which completely bans you from even asking that question. Maybe you could make some GR alternative where the energy-momentum tensor is no longer conserved, but it would be very hard, certainly harder than I'm going to take on to answer such a question. :v: Actually, I doubt it's possible at all, or at least isn't as simple as an "alternative where the energy-momentum tensor is no longer conserved" since you can't just drop the conservation requirement. The energy-momentum tensor is [I]defined[/I] as the conserved current associated with spacetime translations. It's conserved or it doesn't exist at all, and if you've got some theory where it doesn't exist, the EFEs have to change completely.
Can anybody tell me, in theory, what this would look like closer up? Will the effect become less as you get closer, or would being closer to that galaxy be a complete mind fuck?
[QUOTE=Abaddabadon;50802715]I wish I could explore the solar systems in those galaxies.[/QUOTE]
One galaxy is not enough for you?
But really, we can't reach other galaxies or other clusters of galaxies using current thinkable methods of space travel. They keep getting further away from each other, as the Universe expands, so we'd be traveling forever if we wanted to explore an entire new galaxy, or so.
[QUOTE=Matthew0505;50857155]What if we change the question to: What if the Sun were to decay into massless particles with the same mass-energy over 3 seconds?
That way you have a hollow shell of no gravity inside expanding at the speed of light (same speed as the gravity change), which would best simulate mass disappearing.[/QUOTE]
Energy still curves space.
Sorry, you need to Log In to post a reply to this thread.