gravity

MrJack responds to me:

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Isn't Gravity not actually a force?

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A force is a change in momentum with respect to time.Gravity causes changes in momentum with respect to time.Thus, gravity exerts a force.Whether or not this force comes from space-time warpage or actual particles is immaterial. The fact remains that two bodies experience a gravitational pull on it that is measured as a force with units of massdistance/time².Of course, what this means is that evolution is on a more solid foundation than gravity. We still don't really know what causes gravity. But with evolution, we have actually seen a mechanism and can manipulate it directly. And yet, we don't see people trying to claim that gravity is some religious attempt to claim there is no god....------------------
Rrhain
WWJD? JWRTFM!

But there is a significant difference though, isn't there? A force can't bend light, but gravity can because it warps space-time. Isn't that what the famous eclipse experiment showed? That Newton was inaccurate in claiming that Gravity was a force?

As an erstwhile performer myself I think Percipient has confused two different types of actor.There's the kind of actor who gets into it to play roles that are much like him or herself. (That's the kind of actor I am, and that I suspect Rrhain is.) These guys are usually pretty smart, but if they succeed in acting, it's usually in "character" roles. Like, Ben Stein, for instance.Then there's the kind of actor that's so good at acting they're always doing it, and so they play roles because they don't really know who they are. They're usually much more versatile actors, but they're not usually very informed. It is these actors that I think Percipient is thinking of, as they're the stereotypical "fruity" actor. On the other hand, Rrhain may very well be an amazingly well-rounded, versatile actor, and thus my whole theory is garbage. But the phenomenon of geeks in acting is very familiar to us geeks in the theatre.

A force can bend light, because light in motion has mass.

Then how did the eclipse experiment show Einstein was right?

MrJack responds to me:

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But there is a significant difference though, isn't there?

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No. Anything with the right units is a force.That's the beauty behind Einstein's equation E = mc². Energy has units of massdistance²/time². Thus, force through a distance is energy (since force is massdistance/time², multiplying force by a distance gives you units of energy.) Thus, energy and matter are equivalent because their units can be converted into the other.

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A force can't bend light

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It most certainly can. That's why the light bends: It experiences a force. If light is a particle, then it should be affected by forces. Thus, since light is bent by the force of gravity, there is justification for describing it as a particle.

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but gravity can because it warps space-time. Isn't that what the famous eclipse experiment showed?

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No. It showed that light is affected by gravity.

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That Newton was inaccurate in claiming that Gravity was a force?

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No. Gravity is still a force. Anything with the right units is, by definition, a force.We can even measure the relative strengths. A common example shows how much more powerful the electromagnetic force is over the gravitational force. If you drop a clay ball from a height of 4.9 meters, it will take a full second for it to reach that velocity of 9.8 meters per second. But in a mere fraction of that time, the clay comes to rest when it hits the ground. In fact, you could drop that ball from huge heights and still, the ball would take less than a second to stop. And how does it stop? Do the molecules of the ball actually touch the ground? Nope. It's just electrostatic forces.And yet, even though the ball has stopped moving, gravitational forces are pushing the ball and the ground together and are being met with equal and opposite electrostatic forces to prevent them from actually touching.Gravity is a force because it has the right units.------------------
Rrhain
WWJD? JWRTFM!

MrJack writes:

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Then how did the eclipse experiment show Einstein was right?

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Because Newtonian theory was linear while Einsteinian theory was relative. The discrepancy between the theories is not the claim that "gravity is not a force."That is, Newtonian theory predicted that light should bend when travelling around a star, but that would bend by a certain amount. General relativity, on the other hand, predicted a different, greater amount. Specifically, light should be bent by about 1.75 arcseconds when passing the sun which was about twice the amount predicted by Newtonian theory.The eclipse experiment showed that to be the case.Describing gravity as a warping of space-time is a change in conceptualization, not effect.------------------
Rrhain
WWJD? JWRTFM!

I'm still not getting this, sorry.If gravity is just a force, how is it that Newton's theories couldn't predict that light was bent by gravity? But Einstein's theories could? Surely simply showing light is affected by gravity is not enough?I'm right in thinking Einstein showed that gravity warps space-time, yes?edit This was cross-posted with Rrhain's above post. Think I've got it now. Thanks. /edit That can't be right. Let me define a quanity A, let A = (mass of my pen)*(current distance from me to mars)/((time I've spent on the internet today)*(time it will take me to get home)). A now has units mass*distance/time^2, A is surely not a force though?[This message has been edited by Mr Jack, 09-23-2003]

There are also the actors that are very smart about acting but don't apply themselves beyond that. There is only so much time in a day and nobody can be an expert on everything. There are many people who are interested in science but also have interests and excel in something unrelated. Pro basketball player David Robinson has his undergraduate degree in mathematics, for example.That said, acting necessarily requires research if you're going to make a career out of it. If one is going to accurately portray somebody from a particular time period or from a particular profession, then there has to be some investigation into the peculiarities of the characteristics in order to give a convincing portrayal. In the process, you pick things up. The text, itself, will hopefully have been written by an author that researched this stuff in order to make it accurate and simple reading of the script will give you information.Take the musical Chess. I now know the progression of chess champions from Steinitz to Karpov and the years they first became champions. Why? It's in one of the songs. Granted, I have to go through the song in order to spout them off, but they're still in there.Given the huge breadth of theatre, actors get exposed to a huge amount of concepts. Even if they don't get caught up in all of it, they have the opportunity to. Not all professions are so likely to make a person get into aspects of the world around us they never would have encountered before.Of course, I'm the type of person who hates having to look a word up in a paper dictionary...I get sidetracked and end up reading the dictionary and what should have taken 10 seconds ends up taking an hour...and often enough I've forgotten what I was looking up in the first place because I never got that far.------------------
Rrhain
WWJD? JWRTFM!

MrJack responds to me:

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If gravity is just a force, how is it that Newton's theories couldn't predict that light was bent by gravity?

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It could and it did. Newtonian theory claims light is bent by gravity.What it fails to do is accurately describe how much it is bent. This is because Newtonian mechanics is a linear system.When Newton developed his mechanics, he originally showed that force is the derivative of momentum with respect to time. But, under the assumption that the universe is linear, he reduced that to mass times acceleration.However, the universe isn't linear...it's relative. An accelerating body does not have a stable mass. The fundamental concept is correct (force is the derivative of momentum), but the space in which that derivative takes place is not what Newton thought it would be.So according to Newtonian theory, the light passing by the sun would be bent by about 0.8 arcseconds. Einsteinian theory, based on a relative space, predicted a deviation of about 1.75 arcseconds.

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But Einstein's theories could?

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No. Both Newtonian and Einsteinian mechanics predicted that light would bend when in the presence of a gravitational field.They differed on how much and the reason why they differed is because Newtonian physics is linear and Einsteinian physics is relative.

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Surely simply showing light is affected by gravity is not enough?

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Correct. Both claim that that gravity bends light. Therefore, simply showing that light is affected by gravity is not enough to distinguish between the two. Instead, you need to show which one more accurately describes how much light is bent.

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I'm right in thinking Einstein showed that gravity warps space-time, yes?

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No, not really. What Einstein did was show that gravity can be conceptualized as a warpage of space-time. Quantum mechanics, however, suggests the existence of gravitons (though there are formulations of quantum gravity that don't require that).

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Anything with the right units is, by definition, a force.

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That can't be right.

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How could it be any other way? A force is the derivative of momentum with respect to time. Momentum is mass in motion. Therefore, anything that has units of mass in motion per unit time is a force.

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Let me define a quanity A, let A = (mass of my pen)*(current distance from me to mars)/((time I've spent on the internet today)*(time it will take me to get home)).

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"Time you've spent on the internet today" and "time it will take you to get home" are irrelevant, really. What do they have to do with the pen?You can't just multiply objects together and expect to have something meaningful pop out. You have to show how they relate. You've got it backwards: You take a look at something that exists and notice the units on that something. If the units are those of force, then it is a force.

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A now has units mass*distance/time^2, A is surely not a force though?

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Indeed.You have no justification for relating your pen to the amount of time you've spent on the internet. While your calculation results in something with the units of force, it doesn't mean anything.------------------
Rrhain
WWJD? JWRTFM!

Gravity is a misfit. They're still trying to fit it in with the other forces. That's what the Unified Field Theory is all about.Scientists have long been looking for a succinct explanation of the entire universe, and while we've pushed very far, it has still remained elusive.------------------
"Illuminant light,
illuminate me."