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zeromodz
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If I have 2 objects with equivalent mass. Is there anyway I can make one of them have a stronger pull by changing the density? If so are there any equations the help me predict to what extent?
Thanks.
Thanks.
If I have 2 objects with equivalent mass. Is there anyway I can make one of them have a stronger pull by changing the density? If so are there any equations the help me predict to what extent?
Thanks.
Lots of interesting, well written things
Yes.Not being a physicist myself I got lost in the technical mumbo-jumbo.
So what was the upshot?
That the denser object has a more intense gravitational field immediately around it but from a significant distance they would have the same gravitational pull?
I wouldn't use the term "event horizon" in your analogy. Event horizon has a very specific meaning, and I don't think it necessarily applies to your beach ball and marble analogy.This is a very interesting subject. I woke up tonight (as I'm wont to do) with Einstein's (Was it his?) thought experiment about bowling balls and marbles on a trampolene surface to show the bending of space-time. I may have taken the analogy a little far, but I suddenly have a problem...I imagined the experiment with a somewhat more elastic surface (perhaps). If we have a marble, say, that has a very high mass, but a small radius (some super dense material) this would cause a deep curve with a small radius - where as a beach ball would produce a shallow dent with a wide radius. For the two to be attracted, then the event horizons of the two curves need to come into contact with each other.
Umm, I'm not quite sure I follow you here. But I'll take a stab at it anyway. Mass/energy (mass is really just one of several forms of energy) tells spacetime how to curve (how to shape itself). Spacetime curvature tells mass how to move.So this leads to several questions (that woke me up):
1-Is gravity, being a curvature of space-time as opposed to Newtonian force, of equal density itself or does size affect the curvature as well as mass?
It is a principle that laws of gravitation are the same everywhere in the universe (all else being the same except for position). This is just a principle though. Presently, there is no evidence that would indicate that it isn't true.2- Is the flexability of the "surface" (space-time) constant thoughout the universe or is it more apt to curve in some places tha others?
I don't think I understand the question.3- Is the "flexability" such that what I suggested (in my apparant dream) impossible in our universe.
If an object is dense enough, a black-hole will form. Using the analogy of balls on a surface, the dense object would create an incredibly large curvature, near the object. In relativistic terms, the curvature would be large enough, at some close enough distance to the object, that nothing could escape once closer than that distance. This threshold is called the event horizon.4- Is it possible for a super dense object to bend space-time completely around itself - would we know? Maybe this would just be its own little universe/dimension???
There is no threshold. Distance of influence is infinite. There is no distance so far from any mass that spacetime is not curved by it.PS: I knew Event Horizon was specific to black holes, but at 4am here, it seemed as good a descriptor as any even in incorrectly applied - I guessed (correctly) that you would get my gist. Threshold would have been a better term to use - or distance of influence perhaps. :D
There is no threshold. Distance of influence is infinite. There is no distance so far from any mass that spacetime is not curved by it.
Dave, does this mean that if I wiggle my little finger, I wiggle the entire universe (well, a little, anyway)?
How about this.
A star with higher gravitational pull will cause time to pass more quickly.
This increase in time flow *is* gravity.
Yep.
To leave the solar system you would be pulling away from the time stream of your star and moving directly against it. You will age quite quickly.
If time is faster closer to the sun, then why would you not age slower the further you go from the sun?
And if you kept going, eventually reaching the void of absolute space, outside the influence of any star, then would you not stop aging altogether?
A star with higher gravitational pull will cause time to pass more quickly.
Higher mass = higher gravity = slower time.
The closer you get to the speed of light the slower time is going for you compared to a stationary observer.
I think my above post is straying from the original topic. I'm going to start a new thread with it.
For in an open or infinite universe, there would be no official distance markers, no start point, no end point. In other words, there would be no way to determine, between two passing objects, whether both are moving, or one is stationary and the other is moving past it.
Your first paragraph is correct. Your second paragraph does not follow from your first and is wrong.For in an open or infinite universe, there would be no official distance markers, no start point, no end point. In other words, there would be no way to determine, between two passing objects, whether both are moving, or one is stationary and the other is moving past it.
I think that is a very simple and solid case for why our universe is finite, not infinite.
Whether or not the universe is finite or infinite we still have no start or end points or special stationary points.
A finite universe does not have to have a centre, edge or boundary.
Note that the surface of a sphere is finite yet there is no point on the surface that is any more special than any other, no point that could be called start, end, edge or centre. Any coordinate system is utterly arbitrarily applied.
Yes. That and the fact that space itself has expanded since that moment time the light ray was emitted, until the time the ray arrived at Earth. This expansion contributes to a sort of stretching of the wave, giving it a redshift. On cosmological distances, the majority of the redshift of far away galaxies is due to this sort of redshift -- caused by expanding space. That's in addition to any redshift (or blueshift) caused by said object moving through space relative to us.For example when we measure the redshift of a distant star, what is that redshift in relation to? Is it the speed that it's moving away from us?
There is no such thing as the "origin point" of the big bang. The big bang happened everywhere at once (perhaps quite literally -- out to infinite distances, but at the very least, distances far greater than our observable universe). The big bang happened where you are sitting right now, just as it happened 40 billion light years away from you (of course, any object at a distance 40 billion light years away from you now was a lot closer back then).Or the speed that it's moving away from the origin point of the big bang?
In relativity, both special and general, there are no absolute speeds. There are no absolute markers. Everything is in relation to arbitrarily defined coordinate systems, which in practice is in relation to other objects (other galaxies for example). All velocities are relative, is the point.Or is it some sort of absolute speed that can be measure irrespective of any relative marker points? The latter is what I cannot understand.
Velocity only means anything when it is relative to some other object (or objects).I mean, if time moves slower closer to massive objects and faster when away from strong gravitational pull, that seems to say that speed MUST be relative to other objects. No?
And finally, the idea that the speed of light is constant, no matter the speed of its observer. That seems related to this whole topic of absolute speed.
There are several different types of redshift. One type of red shift is most definitely an indication that some things are receding from us irrespective of any cosmological expansion.I also like your explanation of redshift being an expansion of space. This makes more sense to me than if it were measuring "speed."
Unless specified otherwise, one can assume it means "relative to you".To me, speed is a moot point because it must always be followed by the question, "compared to what?"
Light is not like everything else.But I'm still struggling with the speed of light. If every other moving object is subject to relativity, then why is light-speed not relative to anything but itself? Why does light seem exempt from the idea that "in both general and special relativity, there are no absolute speeds."
You're actually asking about something pretty profound. The reason it is profound is that for some reason or another, spacetime warps and curves itself to ensure that everybody and everything measures the same number when measuring the speed of light [Edit: when I say "speed of light" I'm assuming speed of light in a vacuum.]. It's almost as though the whole universe goes out of its way to enforce this -- warping and curving itself by whatever means necessary to make sure every observer observes the same number, no matter what. I'll try to go through two simple examples later (math excluded -- concept only), one dealing with simple special relativity and the other leading toward a first introduction to general relativity.But I'm still struggling with the speed of light. If every other moving object is subject to relativity, then why is light-speed not relative to anything but itself? Why does light seem exempt from the idea that "in both general and special relativity, there are no absolute speeds."