General relativity

Originally posted by robbie carrobie
do you have any illustrations about travelling at the speed of light and what it would appear like, would everything be frozen to a standstill? or any illustrations that helps me grasp the principles for naturally the mathematics will be quite beyond a noob like me.

No. You have mass, so you cannot - repeat: can not - travel at the speed of light. In fact, realising that is one of the fundamentals of understanding relativity.

Richard

Originally posted by Andrew Hamilton
General relativity explains gravity by saying that, when you fall to the Earth, although in a three-dimensional sense you ARE accelerating towards the Earth, in a forth-dimentional sense it is not you that is accelerating towards the Earth but the surface of the Earth that is accelerating toward you! That is because three dimensional space is curved in four dimensions.

Nonsense.

General relativity explains that, when you are accelerating towards Earth, Earth is also accelerating towards you, depending on your relative point of view.

Neither POV is "more correct". Of course, some are more useful... but since either POV is, mathematically, completely equal to the other, both are equally correct. Stating that it's not you who is accelerating is very misleading. You are. So is Earth. From the POV of someone on Mars (with very accurate measuring apparatus...), both of you are accelerating towards one another. All of these are not only correct, but can be shown to be the same.
That is the fundamental point of relativity: once you take into account the position of the observer, it does not matter whether Mohammed goes to the mountain, or the mountain goes to Mohammed. The end result is that mountain and Mohammed are in the same place at the same time. This remains true whether seen from Mohammed's coat-tails, the mountain's roots, or the photon which bounces between the two.

Richard

Originally posted by Shallow Blue
Nonsense.

General relativity explains that, when you are accelerating towards Earth, Earth is also accelerating towards you, depending on your relative point of view.

Neither POV is "more correct". Of course, some are more useful... but since either POV is, mathematically, completely equal to the other, both are equally correct. Stating tha s coat-tails, the mountain's roots, or the photon which bounces between the two.

Richard

“...General relativity explains that, when you are accelerating towards Earth, Earth is also accelerating towards you, depending on your relative point of view. ...”

isn't that what I just said/implied?

Originally posted by Shallow Blue
No. You have mass, so you cannot - repeat: can not - travel at the speed of light. In fact, realising that is one of the fundamentals of understanding relativity.

Richard

As an object is accelerated it increase mass too right? Particles ect.....




Manny

Originally posted by menace71
As an object is accelerated it increase mass too right? Particles ect.....




Manny

Using relativistic mass is a rather outdated practise.

Originally posted by Andrew Hamilton
“...General relativity explains that, when you are accelerating towards Earth, Earth is also accelerating towards you, depending on your relative point of view. ...”

isn't that what I just said/implied?

What you wrote was:

"it is not you that is accelerating towards the Earth but the surface of the Earth that is accelerating toward you!"

It's the first part of this which is wrong. Yes, the surface of the Earth accelerates towards you; but the idea that this could mean that you do not accelerate towards it is precisely what relativity debunks. Both PsOV are correct. You cannot say either is wrong without relapsing into Newtonian principles. There's no fixed frame of reference, anywhere; you get to choose one, but you do not get to say that any of the others are not right.

Richard

Originally posted by Shallow Blue
What you wrote was:

[b]"it is not you that is accelerating towards the Earth but the surface of the Earth that is accelerating toward you!"

It's the first part of this which is wrong. Yes, the surface of the Earth accelerates towards you; but the idea that this could mean that you do not accelerate towards it is precisely what relativity debun et to choose one, but you do not get to say that any of the others are not right.

Richard[/b]

You have taken the wrong meaning possibly because you read it too fast. When I said "it is not you that is accelerating towards the Earth but the surface of the Earth that is accelerating toward you!" I meant in the forth-dimensional sense. In the three dimensional sense you are accelerating towards the Earth -as shown by what I had prefixed that comment with which was “...although in a three-dimensional sense you ARE accelerating towards the Earth, in a forth-dimensional sense ...” so that whole comment was:


“....although in a three-dimensional sense you ARE accelerating towards the Earth, in a forth-dimensional sense it is not you that is accelerating towards the Earth but the surface of the Earth that is accelerating toward you! ...” (my spelling mistake corrected)

Originally posted by Andrew Hamilton
You have taken the wrong meaning possibly because you read it too fast. When I said "it is not you that is accelerating towards the Earth but the surface of the Earth that is accelerating toward you!" I meant in the forth-dimensional sense.

The distinction is nonsensical, whether in the third, fourth-, or tenth-dimensional sense.

Now go forth and be relative.

Richard

Originally posted by Shallow Blue
No. You have mass, so you cannot - repeat: can not - travel at the speed of light. In fact, realising that is one of the fundamentals of understanding relativity.

Richard

he wait a minute I thought that all that would happen to me is that time slowed down, this is a very difficult idea to try to understand, its no wonder you boffins have got such big foreheads. if as i approached light speed, would my mass start to change into pure energy or something else? mass and energy are interchangeable, right? would it like dissipate into space and would I start falling to bits? I seen the millennium falcon go to light speed! 🙂

Originally posted by robbie carrobie
he wait a minute I thought that all that would happen to me is that time slowed down, this is a very difficult idea to try to understand, its no wonder you boffins have got such big foreheads. if as i approached light speed, would my mass start to change into pure energy or something else? mass and energy are interchangeable, right? would it like di ...[text shortened]... nto space and would I start falling to bits? I seen the millennium falcon go to light speed! 🙂

“.... I thought that all that would happen to me is that time slowed down, ...”

If you were wearing a watch and an observer observing you as you whiz past him and watched the speed at which your watch ticked at your closest approach to him then he would see that your watch ticks slower ( and if you were talking or doing something, you would appear to be doing it slower from his perspective than your perspective) than the speed of the ticking he would expect if not taking account of relativity.
But to you, your watch would appear to be ticking just fine at its normal speed and, if you looked at his watch at the moment of the closest approach to him, it would be HIS watch that is ticking slow!
There is no contradiction here and both your observation and his are correct because the speed of time is relative to the frame of reference and which watch is ticking slow depends on your relative motion.


“....if as i approached light speed, would my mass start to change into pure energy or something else? ...”

from the perspective of a 'stationary' (according to some arbitrary frame of reference ) observer observing you, it would appear that your mass would have increased. But from your perspective, it wouldn’t be your mass that has appeared to increased but his!

“...mass and energy are interchangeable, right? ...”

under the right circumstances, correct. I would say the best example of that is in nuclear reactions. But energy was also converted to mass during the Big Bang.

“...would it like dissipate into space and would I start falling to bits? ...”

No. As you approach the speed of light, both your momentum (which is your speed multiplied by your mass) and your kinetic energy (which is equal to half of your mass multiplied by the square of your speed ) would increase in exactly the way you would expect even if you took NO account or relativity. But as your kinetic energy increases, your speed would NOT increase in exactly the way you would expect if you took no account or relativity and that's because your speed would be less than what you would expect because your mass (as seen from a 'stationary' observer according to some arbitrary frame of reference) would increase instead.

I hope that doesn't confuse you 🙂

incidentally, none of that above has much to do with General relativity because all that has to do with special relativity.
I would say special relativity is a lot easier to understand than General relativity, especially the mathematical aspect of it; the mathematics of General relativity is a nightmare in comparison!

Originally posted by robbie carrobie
do you have any illustrations about travelling at the speed of light and what it would appear like, would everything be frozen to a standstill? or any illustrations that helps me grasp the principles for naturally the mathematics will be quite beyond a noob like me.

Actually one of the points of 'special relativity' is that you can't travel AT the speed of light. although you can get really close.

It works like this;
You have a gun with a muzzle velocity of 300m/s.
You sit at the side of the road and shoot a road sign and you measure the speed your bullet to be 300m/s
Now you do the same thing but sitting on the front of a car doing 50m/s.
Now you measure the speed of the bullet from your gun to be 300+50m/s, I.E. your speed plus the speed of the car.

So far so normal. But Einstein realised that light was different.

Maxwell discovered that light was caused by interactions between travelling waves of electric and magnetic forces. the oscillating magnetic field creates the electric field and the oscillating electric field creates the magnetic, with the energy of the light wave being moved back and forwards from electric to magnetic and back again.

The crucial part of this is that the magnetic and electric fields have to be moving for this to work.

Therefore Einstein reasoned like this;

If I chase a beam of light and somehow go fast enough that I can match its speed then it would appear to be stationary.
But stationary light can't exist. thus the beam of light wouldn't exist.

As two major law's/principles of physics are that energy can't be created or destroyed, and that the laws of physics are the same for all observers. This situation must not be possible.

The solution is that all observers measure the speed of light (in a vacuum) to be the same regardless of the observers velocity.

The consequences of that are that it is impossible to make matter travel at or faster than light speed and that the faster you travel the slower time passes.

This means you can never travel at or more than the speed of light so you can never get stationary light beams and that as you approach the speed of the light beam you are chasing time travels slower for you so your measurement of the speed of the light beam will always be the same.

The reason for a particle/object with mass (i.e. matter) can't travel at or faster than light speed is that not only does time slow down for fast moving objects but they increase in mass as well. thus the faster you move something the heaver it gets and the harder it gets to make it go faster.

The mathematics of this does actually allow for particles that ONLY travel at ABOVE the speed of light, dubbed tachyons, so beloved in star trek.
They have never been detected and don't exist in most of the current contenders for 'theory of everything'.

One of the problems with mathematical descriptions of the world is that sometimes you can get more than one answer, for example of you do the math for the trajectory of a shell fired from a gun you will get two answers for where it hits the ground,.

One is the one you expect where the shell goes forwards and, hopefully, hits the target.
And another where the shell goes backwards through the gun and hits the ground behind it.

The second solution is obviously not physical and is thus ignored.

however there are some instances where the maths turns out to be right and the 'second solution' is a real phenomena.

The discovery of Anti-Matter was one such instance, The maths predicted a mirror image of ordinary matter should exist, most people thought it was non physical but a few years later they actually detected particles in particle collider's that matched the properties of this anti-matter.

Tachyons probably don't exist, and are a purely mathematical construction with no basis in reality, however if they do exist, special relativity says that they not only travel faster than light but also travel backwards in time.

All that said, this does not necessarily preclude FTL travel, by other means, (read spacial warping, wormholes, hyperspace ect) but your never going to do it by getting a big rocket and blasting your way through space.

EDIT: oh and there are three kinds of relativity:
Principle of Relativity, Invented by Galileo Galilei
Special Relativity, Invented by Einstein in 1905
General Relativity, Invented by Einstein in 1915

In very basic terms;
The first says the laws of physics are the same for all admissible reference frames.
The Second deals with objects travelling at a constant speed near the speed of light, and the equivalence of mass and energy.
The third deals with Gravity and objects accelerating with the existence of 4 dimensional 'space-time' as the explanation for how gravity works.

Originally posted by googlefudge
Actually one of the points of 'special relativity' is that you can't travel AT the speed of light. although you can get really close.

It works like this;
You have a gun with a muzzle velocity of 300m/s.
You sit at the side of the road and shoot a road sign and you measure the speed your bullet to be 300m/s
Now you do the same thing but sitting on istence of 4 dimensional 'space-time' as the explanation for how gravity works.

you sir have blown my mind! why didn't they teach this stuff when i was doing physics at school? all we got were ticker tapes and trolleys! I know not what you do but you have the makings of a great teacher!

Originally posted by robbie carrobie
can anyone explain to me in layman's terms what general relativity is? or more
importantly can you provide references or illustrations to explain what it is, for i have
looked on the net and its not so easy to grasp, for me anyway.

In simplest terms it means that the perspective of spacetime is relative... light travels relative to the observer. It also goes into the fact that you travel through spacetime at the speed of light.. the speed that you go through the space part is relative to the speed that you go through the time part but you are always traveling through spacetime at the speed of light.

EX

Assume I can run 149 896 229 m/s(half the speed of light), I am racing a beam of light and you are watching.

To you light is only traveling 149 896 229 m/s faster than me and is only getting that far ahead every second. However, to me it is traveling 299,792,458 m/s(speed of light) faster and getting ahead of me that much faster.

get it? well thats the simplest aspect of the whole thing anyway the rest is rather more complicated.