1. I Why do objects fall along the ripples of spacetime?

When people try to explain how gravity works, the following example is constantly used . However, I don’t understand how this explains HOW gravity works. By using this example, gravity itself is used as a bias to explain how gravity works. How can explain gravity by saying “things fall along...
2. B How constrained are the initial conditions of the universe?

Do we know? Do we have any idea? There seems to be 2 schools of thought. 1. The initial conditions can be almost any value with universes inflating with different laws of physics. This is the multiverse and string theory 10^500 false vacua view. 2. The initial conditions are more restrained...
3. A Effects of gravity throughout space-time?

Can the effects of gravity possibly extend through time? Is there a natural law that forbids this? Could this be a possible explanation for dark matter?
4. A Do Holographic Screens eliminate holographic dualities?

Do Holographic Screens eliminate the need of finding holographic dualities? There are various models in physics based on the famous holographic principle (https://en.wikipedia.org/wiki/Holographic_principle) This does not always work since in these models we must find a correlation between two...
5. A Is there any theory that can be modeled in any type of space?

Is there any theory in physics that can be modelled in any type of space (Hilbert space, Euclidean, Non-Euclidean...etc)? And if yes, could that theory also contain/be compatible with all types of (physical) symmetries?
6. I Is time bidirectional in a black hole?

I just watched a youtube video saying that somewhere in a blackhole, time is bidirectional (can go to the future and can go to the passed), but space is one-directional. Any introduction material on this subject? Thanks in advance!
7. B Could singularities be just rips in the space-time fabric?

First off, this is just an assumption. My knowledge of the field is extremely limited and I beg you to come and correct my mistakes, so I can learn. So, I guess we all know how that space-time fabric is bended by gravity. When a star dies, all of the atoms are brought extremely close...
8. B How did Einstein come up with the thought of a space fabric?

I've always wondered how we came to come up with such an idea. Was he one day sitting around and thinking, then made a random assumption and go "ah hah!". Or did his idea come up through his calculations on the nature of how gravity should cause interaction? Is their a literal fabric of space...
9. B Motion (rest/velocity/acceleration) vs Time

Why Space/TIME? I feel Motion affects Time, not the contrary. Thanks for claritication (no Math please).
10. B Do photons interact with spacetime?

The way I understand this is that Relativity says space-time is like a field that's affected by the way mass moves through it. Photons are massless so is this why the speed of light is the same in all reference frames?
11. Ek vs engine power in cars and space

Help me please:) (1) An idealized engine with constant torque curve means constant acceleration. So for example if there is no air resistance and no frictions and car is on fixed gear and at 3000Rpm it produces 50Hp so at 6000Rpm will produce 100Hp. So he doubles the speed , doubles power and...
12. I Question about time and space

if the earth were set between 2 Sun (our sun) in the distance which the time passes the exact same as it is right now, does the distance between us and each sun would be the same as it is right now?
13. I How can General Relativity explain the Moon drifting apart from Earth

According to various sources, the Moon is separating from Earth 4 cm every year. I’ve searched for the explanation and I’ve found the following: The friction the seas and oceans from the Earth make with it’s soil causes the Earth’s rotation to slow down. This causes the Moon to speed up...
14. I Does a metric exist for this surface?

I have a surface defined by the quadratic relation:$$0=\phi^2t^4-x^2-y^2-z^2$$Where ##\phi## is a constant with units of ##km## ##s^{-2}##, ##t## is units of ##s## (time) and x, y and z are units of ##km## (space). The surface looks like this: Since the formula depends on the absolute value of...
15. B Does black hole stop light or time?

I have been told the speed of light is constant and does not waiver. This would make sense as light has no mass I am aware of. Pictures taken during a solar eclipse seem to prove gravity bends light. Could it be however that the light is not bent, only the time/space light is traveling through...
16. I Is there an analog to Einstein's field equations for 2D?

I am not familiar with tensors and I would like to know if it's possible to understand GR without using them. I imagine we use them to describe four-dimentional space-time, because a regular vector or matrix wouldn't be enough. Is there an analog of Einstein's equations for a 2D space (plane)...
17. G

B How is a Vaccum mathmatically described?

Anyone know what books and astrophysicist has this knowledge? Thank you, Greg
18. B Mechanism of Curvature of Space

Hi all, How does matter curve space (what's the mechanism)? Does this Curvature happen instantaneously or does it happen at light speed? Thanks in advance.
19. B Is it possible to reach the singularity?

The question is; After an object goes through the event horizon, is it possible for the object to reach the singularity? As far as i know, singularity, bends space down and actually space moves faster than light towards the singularity. But what tells us that the singularity's bending has a...
20. I The name of the 3+1 metric where time is normal to space?

I am interested in looking at the metric where time is everywhere normal to space, so gta=0 everywhere, where t is the time coordinate and 'a' is any of the space coordinates. I'm finding it hard to look up in the literature: does it have a name that I can search for? My main interest is in...

We are told that space is expanding and that the rate of expansion is speeding up. However, as relativity shows that space and time are inextricably linked, does this mean that time is expanding too?
22. B Dimension of the photograph of a four dimensional world?

If time is a dimension, what would be the dimension of a photograph in such a space?
23. B If energy is created with expansion and it has no limit...?

Then is potential energy infinite (potential energy=energy that can be created)
24. B Is dark/vacuum potential energy infinite?

And virtual particles potential energy is infinite too? As more and more dark energy is created does this mean that the potential energy of dark energy is infinite? Does that happen for virtual particles in vacuum and vacuum energy too?
25. I Is vacuum energy infinite? If it is, how and why?

https://en.m.wikipedia.org/wiki/Vacuum_energy And it is this type of energy dark energy or a form of it?
26. I Spacetime and effects of being super close to the Sun

I have been wondering about space time and how it works like satillites putting corrections in there clocks by a few nano seconds a day because of gravity or lack of it!! But I have also wondered about the effects of being super close to the sun and time that we observe there looking back at...
27. I Would there be spacetime w/o energy

If there was no mass/energy would space time still exist? In other words, does on space time only exist because of an interaction between two points of energy?
28. I Metric for quasar

Hello I just got interested into quasars and I have a question:What metric do you use for quasars?
29. Age difference problem due to space travel

Homework Statement The identical twins Speedo and Goslo join a migration from the Earth to Planet X, 19.0 ly away in a reference frame in which both planets are at rest. The twins, of the same age, depart at the same moment on different spacecraft. Speedo's spacecraft travels steadily at 0.945c...
30. I Did the Big Bang separate space and time

Hello everyone, I've come across a problem that i can't solve but which i find really interesting. I'm not here to ask where the big bang was because i've already read enough about that is was a singularity, so you could say that is was everywhere. But here my problem comes in, if the big bang...