Theory Of Relativity

[Lotto]

No. It's about adding speeds together. Let me try to rephrase it.

Imagine that the person on the car wants to know how fast the train is going. He can measure the speed of the train relative to car (20mph). And he knows how fast he is going by measuring speed of objects on the ground (40mph). Normally, you'd expect him to conclude that the train is moving at 40mph + 20mph = 60mph. But a person on the ground, measuring the train's speed, will see a number that is somewhat less than 60mph.

Davidtourniquet mentions a more extreme example from which you see that speeds can't just add to each other. Two objects can move at more than half the speed of light, but they must still move at less than speed of light relative to each other. Clearly, you can't just add velocities.

There are formulae that correct for this stuff, of course.

Ah, so the speed of the car relative to the person on the train is 20 mph. The speed of the car relative to the person observing is 40 mph and the speed of the train relative to the person observing the train is 60 mph, both the speed of the train relative to the person observing both at the same time is not 60 mph, it would be something less, correct or incorrect?

[K^2]

No, no. One of these three speeds is off. If the car moves at 40mph relative to ground, and 20mph relative to train, then the train is moving at less than 60mph. If the train is moving at 60 relative to ground, and car is moving at 40 relative to ground, then train relative to car is moving at more than 20mph.

Point is, if you know two of these numbers, you can figure out the third, but it won't be through straight addition/subtraction.

I think I'm making it a bit more confusing than it really is, but I am also starting from the wrong end.

If you are really interested in some details, there is a very good book by Einstein himself written for persons with no special background in physics. There is no scary math. Just many well-explained thought experiments showing why Relativity needs to be that way, and in the end, mentions a few real experiments confirming it. Fortunately, the copyright has expired, so you can read it for free on Google Books:

Relativity - The Special and General Theory

But if you are not a fan of reading from screen, it tends to be easy to find in libraries.

[_Famrir_]

well to the untrained mind having a universal speedlimit like that is kinda ludicrous dont you think?

[Crazy Tom]

The laws of Physics as we know them now are going to change, its just inevitable. Right now it goes against everything that we know about physics. But 200 years ago they said the same about what we are doing now. Things change. One day I have a feeling that will reach FTL speeds. But we just can't do that now because it goes against everything we know about physics.

Actually... no. Even through through our understanding of physics may evolve, physics itself will not. The same events that happen today will be happening tomorrow, and the day after, and so on, the speed of light barrier has been tested in particle accelerators, it will not change, you will not be able to exceed it.

The sad fact is that in all probability, FTL will turn out to be nothing more than a wistful daydream and we'll have to go slogging around the universe the old fashioned way, still, it's not all bad, once you're immortal, spending a few years in transit doesn't look so bad anymore.

By the time we can bend physics around our then metaphorical little fingers to allow FTL, we won't be resembling homo sapiens anymore than an anemone resembles a supercomputer. But that makes for bad TV, so we never see it.

[K^2]

well to the untrained mind having a universal speedlimit like that is kinda ludicrous dont you think?

Your perception of the world surrounding you is faulty. Your brain is trained to perceive the world in the simplest possible way so as not to overtax it. (The brain, that is, not the world.) Common misconceptions are numerous, and I'll list a few just to give you some idea.

When you drop an object, it does not accelerate towards ground. Ground accelerates towards it.

When you "touch" something, there is no physical contact. You are interacting with that object via electric fields.

A solid object is mostly empty space. Again, it's just the electric fields that prevent you from passing through. There is nothing actually "solid" there.

Difference between past and future is only in which one you can remember. They both have already "happened".

And these are just some everyday things off the top of my head. The rabbit hole is very deep.

[Lotto]

Your perception of the world surrounding you is faulty. Your brain is trained to perceive the world in the simplest possible way so as not to overtax it. (The brain, that is, not the world.) Common misconceptions are numerous, and I'll list a few just to give you some idea.

When you drop an object, it does not accelerate towards ground. Ground accelerates towards it.

When you "touch" something, there is no physical contact. You are interacting with that object via electric fields.

A solid object is mostly empty space. Again, it's just the electric fields that prevent you from passing through. There is nothing actually "solid" there.

Difference between past and future is only in which one you can remember. They both have already "happened".

And these are just some everyday things off the top of my head. The rabbit hole is very deep.

Ok, those two concepts I can't wrap my head around at all....Well, the first one I can't wrap my head around at all. How does the ground accelerate towards the objects when it doesn't move, is it the gravity accelerating towards the object to pull it down?


Ok, I know the past has happened but the future?

[Heaven]

oversimplification is making these statements unintelligible.
the first statement should actually be both the object and the ground accelerate toward each other (they both experience equal force in opposite directions). since the Earth is massive however its acceleration is negligible.
the second statement is too obscure to understand what hes talking about, entropy or determinism?

[K^2]

Heaven, you are incorrect. General Relativity tells us that neither the center of mass of the earth, nor center of mass of the object accelerate. They simply follow their respective geodesics. However, the surface of the earth does accelerate outward away from center at acceleration of 9.8m/s² in any inertial frame of reference.

The position of the surface is a 4-vector (-ct,r,theta,phi) in spherical coordinates centered at Earth's center of mass, which is a good choice for inertial reference frame. (Earth here is assumed to be spherical, which is a fair approximation to within precision being used.) Theta and phi are irrelevant, and can be taken to be zero due to symmetry. The proper velocity of the surface is (c/sqrt(1-2*G*M/(r*c²)), 0, 0, 0). If you take the covariant derivative of this vector along itself, you will get acceleration: (0, G*M/r², 0, 0). That is, surface accelerates along radial direction at the rate stated above. (See Schwarzschild Metric for some references.)

In terms of determinism vs entropy - both. In a closed system, entropy is conserved. Why the entropy appears to increase and how that gives rise to apparent flow of time are complex topics, so I won't go into details. Simplest way to view this, however, is through Many World Interpretation of Quantum Mechanics, where there are more possible future states than possible past states for any particular current state of the system. This would result in increasing entropy in any one particular history. (See Many-Worlds Interpretation.)

@Lotto, these things aren't trivial. Explaining them to a graduate Physics major takes some time. Explaining them to someone who knows very little physics takes a very, very long time. The book I linked goes into some of it on the topic of accelerations. If you want to read more about Many-Worlds, I've seen a couple of good books and I can recommend some that you'd be able to follow.

[TBA]

Those statements are some pretty heavy mindscrews... The time one is interesting, what do you mean with 'Many Worlds'?

[K^2]

Try reading the wiki article on Many-Worlds Interpretation. It's not great, but it will give you a general idea.

[Medicman]

Actually... no. Even through through our understanding of physics may evolve, physics itself will not. The same events that happen today will be happening tomorrow, and the day after, and so on, the speed of light barrier has been tested in particle accelerators, it will not change, you will not be able to exceed it.

The sad fact is that in all probability, FTL will turn out to be nothing more than a wistful daydream and we'll have to go slogging around the universe the old fashioned way, still, it's not all bad, once you're immortal, spending a few years in transit doesn't look so bad anymore.

By the time we can bend physics around our then metaphorical little fingers to allow FTL, we won't be resembling homo sapiens anymore than an anemone resembles a supercomputer. But that makes for bad TV, so we never see it.

True. I knew what I was trying to say I just couldn't word it correctly. Thanks for correcting that for me.

As for the Hyperdrive and FTL Check this out. I think its a pretty interesting read. And no matter what anyone says you gotta love what those guys at CERN are doing! http://http://www.popsci.com/technol...on-well-theory

[Aer'ki]

Heaven, you are incorrect. General Relativity tells us that neither the center of mass of the earth, nor center of mass of the object accelerate. They simply follow their respective geodesics. However, the surface of the earth does accelerate outward away from center at acceleration of 9.8m/s² in any inertial frame of reference.

You know, your continual mumbo jumbo is getting real annoying. You think that by throwing a lot of scientific terminology around it will make people think you know what you're talking about...except that I understand this stuff in the first place so I can detect your theoretical B.S.

HEAVEN...you are correct. All matter pulls all other matter towards it assuming some other force doesn't trump gravity(like magnetism). Right now, you are being pressed into the ground by gravitational ACCELERATION. That's why you can grip the ground with your feet and walk instead of floating around. It has to be a constant acceleration to achieve the compression.

Now, does the Earth move towards you? In theory, yes, but the amount moved is so negligible its almost not worth measuring. However, the path of the Earth in orbit will show the variation as opposed to measuring things on the 'ground.' So it does matter, just not very much.

And for the record, physics isn't that complicated once you break it down into fundamental principles...the mumbo jumbo is complicated because you've got con men trying to sell you crap that isn't true and they go to great lengths to do so...often wearing you out until you finally say you don't care.

For all the real physicists out there(or people who care) here are a few fundamentals to consider.

1.Space doesn't exist outside of academia. If it doesn't exist, it can't bend or distort.
2. Time doesn't exist outside of academia. There isn't a substance or energy called time that can be manipulated. Therefore Time is a constant.
3. Gravity is a constant as far as we can tell, and extends to infinite distance diminishing as it goes(the infinite part is academic since we can't measure it)
4. Earth is not the center of the universe and measurements shouldn't be taken from our point of view.
5. Relativity in the basic principle is real...there is no gridded baseline for everything in the universe to be measured off of. All speeds are relative to the point of measurement(highway speeds are measured compared to the ground). Is one object moving or another? Both are, from a certain point of view. Impact velocities are the same regardless which is 'moving' and which is 'getting hit'.
6. Because all speeds are relative, there can be no 'absolute speed limit', thus faster than light travel RELATIVE TO EARTH is possible.

[Heaven]

Aer'ki thanks for the support but K^2 is not wrong
he's just talking from a GR perspective, whereas what I said is the Newtonian view.
in GR gravity is treated as spacetime curvature instead of the Newtonian force view.

[Flyboy]

You know, your continual mumbo jumbo is getting real annoying. You think that by throwing a lot of scientific terminology around it will make people think you know what you're talking about...except that I understand this stuff in the first place so I can detect your theoretical B.S.

HEAVEN...you are correct. All matter pulls all other matter towards it assuming some other force doesn't trump gravity(like magnetism). Right now, you are being pressed into the ground by gravitational ACCELERATION. That's why you can grip the ground with your feet and walk instead of floating around. It has to be a constant acceleration to achieve the compression.

Now, does the Earth move towards you? In theory, yes, but the amount moved is so negligible its almost not worth measuring. However, the path of the Earth in orbit will show the variation as opposed to measuring things on the 'ground.' So it does matter, just not very much.

And for the record, physics isn't that complicated once you break it down into fundamental principles...the mumbo jumbo is complicated because you've got con men trying to sell you crap that isn't true and they go to great lengths to do so...often wearing you out until you finally say you don't care.

For all the real physicists out there(or people who care) here are a few fundamentals to consider.

1.Space doesn't exist outside of academia. If it doesn't exist, it can't bend or distort.
2. Time doesn't exist outside of academia. There isn't a substance or energy called time that can be manipulated. Therefore Time is a constant.
3. Gravity is a constant as far as we can tell, and extends to infinite distance diminishing as it goes(the infinite part is academic since we can't measure it)
4. Earth is not the center of the universe and measurements shouldn't be taken from our point of view.
5. Relativity in the basic principle is real...there is no gridded baseline for everything in the universe to be measured off of. All speeds are relative to the point of measurement(highway speeds are measured compared to the ground). Is one object moving or another? Both are, from a certain point of view. Impact velocities are the same regardless which is 'moving' and which is 'getting hit'.
6. Because all speeds are relative, there can be no 'absolute speed limit', thus faster than light travel RELATIVE TO EARTH is possible.

I was under the impression that time was relative as it is dependent significantly on the strength of gravity, thus time progresses at differing rates depending on the gravity fields present. Einstein's twin paradox and all that.

Furthermore, am I not correct in stating that there is some measurable form of time - the plank length? That is to say, time doesn't flow, but rather skips along tick by tock like a clock does?

[Crazy Tom]

True. I knew what I was trying to say I just couldn't word it correctly. Thanks for correcting that for me.

As for the Hyperdrive and FTL Check this out. I think its a pretty interesting read. And no matter what anyone says you gotta love what those guys at CERN are doing! http://http://www.popsci.com/technol...on-well-theory

Welcome, but link doesn't work.P

On a tangent, do you know about Orion's Arm?