I don't understand Theory of Relativity: A)I am not clever B)Nothing to understand

[ajb]

Based on it? If you by that mean that they use the mathematical model of special relativity to explain some things, then yes.

You don't have to build special relativity into quantum (or classical) field theory, but as one is looking for models of physics it is natural to do so. From a mathematically point of view it can be best not to and use mathematically nicer Euclidean groups. Anyway, the key thing is that you want your physical theory, both classically and quantum mechanically to be Lorentz invariant. That is it respects the symmetries of nature as encoded in special relativity. This leads to some fascinating links between group representation theory and what kinds of particles we can find in nature, the uniqueness of the vacuum and so on... That is another story really.

 

Also, I did 'chuckle' a bit when you mentioned string theory. The basic simplest string theories (flat background) also have special relativity 'written into them'. It depends exactly on the formulation you use as to exactly how this is expressed, but again basically the theory respects the symmetries of nature as encoded in special relativity.

 

I think that in 10-20 years we will come to understand (if we are open enough) that quantum mechanics (or a subset/advancement of these field) create the observable effects of curved space time, not in any way the other way around.

I am not really sure what you are saying here. We know that matter effects space-time via the Einstein field equations. We also know that we can study quantum theory on curved space-times, with all the problems that involves.

Edited April 12, 2015 by ajb

[michel123456]

My impression is that a lot of people argue that they understand Relativity although they don't. The Internet is full of "explanations" that explain nothing, adding confusion to the innocent mind. I have even seen strong arguments raised between people who both believe they understand Relativity ending with insults on both sides.

 

As I posted before, to me, Relativity is a Theory of observation.

Relativity describes rather accurately what an observer will observe and measure, and how one observation can be transformed into another for another observer.

That's it.

 

When this Theory is used to describe the Universe, I don't know.

[studiot]

 

As I posted before, to me, Relativity is a Theory of observation.

 

I did not see that post, but it is an interesting (and likeable) way of putting it. +1

 

Does your presentation run to including any form of uncertainty principle?

Your exposition above was completely definite.

Edited April 12, 2015 by studiot

[swansont]

My impression is that a lot of people argue that they understand Relativity although they don't. The Internet is full of "explanations" that explain nothing, adding confusion to the innocent mind. I have even seen strong arguments raised between people who both believe they understand Relativity ending with insults on both sides.

 

As I posted before, to me, Relativity is a Theory of observation.

Relativity describes rather accurately what an observer will observe and measure, and how one observation can be transformed into another for another observer.

That's it.

 

When this Theory is used to describe the Universe, I don't know.

 

 

That's because science is based on observation. The one way we can learn about how things behave is by comparison of models with reality. There are numerous threads where it is explained that science deals with how nature behaves, and not the fundamental reality of nature. The latter is metaphysics. So when you say "Relativity describes rather accurately what an observer will observe and measure" then I say yes, that's exactly it. That's what all science does. Anything that can't be observed and measured is ignored, because it doesn't matter.

[Questionist]

I'm not even going to dignify the post above this one since it includes direct and personal insults.

Questionist

 

You mentioned earlier about light bending around a star. Here's a picture of the light of a galaxy 12 billion light years away, bending around another galaxy 4 billion light years away, that's in our line of sight. This phenomenon was predicted by General Relativity. It's called an Einstein Ring.

 

 

http://phys.org/news/2015-04-alma-einstein-stunning-image-lensed.html

Yes, Yes of course light bends around stars. But not because something non-tangible such as space-time, bends.
Because nothing can't bend.

People need to understand my objections with the theory. It is not that its calculations are incorrect, it is that it is currently lacking physical explanations.
It's as back when some dudes postulated that quarks existed or should exist based on their calculations. But they didn't invent them, claim their physical realities and so on. Instead through experiments some of their attributes were shown to be real and their actual structure and shape is still unknown and they obviously exist in more varieties than the two imagined..

You don't have to build special relativity into quantum (or classical) field theory, but as one is looking for models of physics it is natural to do so. From a mathematically point of view it can be best not to and use mathematically nicer Euclidean groups. Anyway, the key thing is that you want your physical theory, both classically and quantum mechanically to be Lorentz invariant. That is it respects the symmetries of nature as encoded in special relativity. This leads to some fascinating links between group representation theory and what kinds of particles we can find in nature, the uniqueness of the vacuum and so on... That is another story really.

Also, I did 'chuckle' a bit when you mentioned string theory. The basic simplest string theories (flat background) also have special relativity 'written into them'. It depends exactly on the formulation you use as to exactly how this is expressed, but again basically the theory respects the symmetries of nature as encoded in special relativity.


I am not really sure what you are saying here. We know that matter effects space-time via the Einstein field equations. We also know that we can study quantum theory on curved space-times, with all the problems that involves.

 

 

From my understanding early string theorist were lambasted because their theory did not manage to fit everything, the theory has since been modified. But in fact string theory is an attempt to tie in all the knowns that would not fit General Relativity.

 

 

As I posted before, to me, Relativity is a Theory of observation.

Relativity describes rather accurately what an observer will observe and measure, and how one observation can be transformed into another for another observer.

That's it.

 

This I would agree with. The problem is that people actually claim that the different observations are in fact real changes. Different words are used depending on different texts.
I found this good example on the web:

At .9 times the speed of light, the factor becomes 2.294157338705618. Finally, the effects of relativity become significant. What does this factor mean though? If you were in a spaceship traveling at .9 times the speed of light:
1) the ship's mass (and you) would increase by a factor of 2.294
2) the ship (and you) would contract in the direction of travel by 2.294, meaning a 300 foot ship would shrink to 130.77 feet.
3) Perhaps the most interesting change is that 1 year to you would seem to be 2.294 years for someone back on Earth.

 

 

Obviously a rocket traveling close to the speed of light would from earth be measured as if taking longer than it actually does to the distance that light has to travel. Any object traveling at any speed from a point of reference at distance of that object takes longer to measure because of the reflection of that object taking time to reach the observer.

But those claiming there would be an actual physical change (and there are many of them) are those who both frighten me and make me laugh.
Or even claiming that the ships form would actually change. All that would change is the observation of the ships form, that would mold into itself. Nothing else, at least there is no evidence for anything else.

 

Edited April 12, 2015 by Questionist

[studiot]

Don't feed the Trolls

[Strange]

As I posted before, to me, Relativity is a Theory of observation.

Relativity describes rather accurately what an observer will observe and measure, and how one observation can be transformed into another for another observer.

That's it.

 

And that is true for all scientific theories. That is how science works.

 

When this Theory is used to describe the Universe, I don't know.

 

As the only way we can know about the universe, that is why a theory based on those observations is considered a good description of the universe.

 

(Obviously, religion or metaphsyics may say that there is more to the universe than what we can observe. But they have the luxury of not being constrained by evidence.)

Edited April 12, 2015 by Strange

[Mordred]

I'm not even going to dignify the post above this one since it includes direct and personal insults.

Yes, Yes of course light bends around stars. But not because something non-tangible such as space-time, bends.

Because nothing can't bend.

 

People need to understand my objections with the theory. It is not that its calculations are incorrect, it is that it is currently lacking physical explanations.

It's as back when some dudes postulated that quarks existed or should exist based on their calculations. But they didn't invent them, claim their physical realities and so on. Instead through experiments some of their attributes were shown to be real and their actual structure and shape is still unknown and they obviously exist in more varieties than the two imagined..

 

 

 

From my understanding early string theorist were lambasted because their theory did not manage to fit everything, the theory has since been modified. But in fact string theory is an attempt to tie in all the knowns that would not fit General Relativity.

Unfortunately all the points in this post are inaccurate. It's apparent from just this post alone that you never truly looked at either of the above theories in mathematical detail. If you had you would realize that the term space is simply volume.

 

Space time is any geometric model of space with the time component as a vector.

Gravity only affects mass. So gravity can only influence particles.

Space time is a geometric distribution of gravity upon the particles contained within a volume of space. If you look at the stress energy tensor you would realize it's energy density/pressure related.

[Questionist]

Unfortunately all the points in this post are inaccurate. It's apparent from just this post alone that you never truly looked at either of the above theories in mathematical detail. If you had you would realize that the term space is simply volume.

 

Space time is any geometric model of space with the time component as a vector.

Gravity only affects mass. So gravity can only influence particles.

Space time is a geometric distribution of gravity upon the particles contained within a volume of space. If you look at the stress energy tensor you would realize it's energy density/pressure related.

What all points.

If time was just a vector I would be fine with that, I've said this many times over. Love for puppies can be a vector.

Again you have people in this and the other thread unable to agree with each other on basics.

 

It's a freaking religion with deviant currents.

Edited April 12, 2015 by Questionist

[Strange]

Yes, Yes of course light bends around stars. But not because something non-tangible such as space-time, bends.

Because nothing can't bend.

 

What "bends" is the geometry use to define the measurements of space and distance between events. So, you are right, there is no physical "space-time" that bends. It is just that the mathematical model describes the curvature of geometry. (Did you ever come across non-Euclidean geometry in your studies?)

 

 

People need to understand my objections with the theory. It is not that its calculations are incorrect, it is that it is currently lacking physical explanations.

 

The physical explanation is that the geometry of space time is affected by mass, energy etc. If you don't find that sufficient, there isn't much anyone can do. You are just saying you don't like the way the theory works, not that the theory is wrong.

 

It's as back when some dudes postulated that quarks existed or should exist based on their calculations. But they didn't invent them, claim their physical realities and so on. Instead through experiments some of their attributes were shown to be real and their actual structure and shape is still unknown and they obviously exist in more varieties than the two imagined..

 

As we can only observe quarks indirectly, it is possible that they don't really exist and are just a good model for how protons and neutrons behave.

 

Actually, we can't observe anything directly, which is why science is all about creating useful models rather than "truth" or "reality".

[ajb]

From my understanding early string theorist were lambasted because their theory did not manage to fit everything, the theory has since been modified. But in fact string theory is an attempt to tie in all the knowns that would not fit General Relativity.

The first applications of string theory was to hadons. This fell out of fashion as QCD was developed. The interesting thing about string theory is that the graviton is necessarily included the spectra. This is quite amazing as the theory does not mention gravity at the start. The promise of a unification scheme via string theory (or now M-theory) has not be realised. However, today it remains the best framework we have to seek such a unification scheme.

[Strange]

Science deals with the fundamental reality of nature.

 

No. That would be metaphysics (or religion).

 

Science just builds the best possible models of what we can observe.

 

Thus theories concerning "fundamental particles".

 

That doesn't mean they are describing "fundamental reality" just that, at the moment, those particles are thought to be indivisible. There are a number of theories proposing that they are in fact made up of "lower level" particles.

 

edit: In general this is the most convincing experiment ever performed: http://en.wikipedia.org/wiki/Hafele–Keating_experiment

But there are objections to it, and alternative explanations. Still it amazes me that none of you have taken it up, not even in other threads I'm looking through.

 

Perhaps you could identify one of those objections so it can be discussed?

[ajb]

Science deals with the fundamental reality of nature. Thus theories concerning "fundamental particles". Get your own stuff straight.

Questions of 'reality' are for metaphysics, which is a branch of philosophy. Swansont is right, when all is said and done, science is about what we can measure. One has to employ mathematical concepts and tools here for which one does not usually question if they "exist" or are "real". The only things that are real are what we can measure.

 

p.s. Please watch your language.

[imatfaal]

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Questionist.

 

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[Mordred]

http://en.m.wikipedia.org/wiki/Stress%E2%80%93energy_tensor

 

String theory was never intended to replace GR. Lol this was suppose to be part of my previous post. Phone didn't update

Edited April 12, 2015 by Mordred

[Questionist]

My god man, I'm not going to try anymore, I'm done lazy, thanks for being a shining beacon of objective justice.

Here is how I understand Relativity (in a way that other people may laugh at)
_it has nothing to do with relativity. Relativity principles were known by Galileo and Newton.
_it has to do with the introduction of an absolute, the speed of light, and the way to conciliate this observational absolute with the well-known principles of relativity.

Following Galileo and Newton, the concept of speed is relative: there is no such thing as an absolute speed, and under this premise talking about a constant or maximum speed is pure nonsense.

Following Einstein, there is an absolute speed, C, which is constant, and which no massive object can attain. In order to make this concept "fit" into the older concepts of relativity, Einstein had to stretch and squeeze the concepts of Space & Time. In fact Einstein's Theory could have been named "Theory of Absolutivity" or "Theory of Constancy".

In other words, Einstein's Relativity transforms Galileo's "nonsense" into a physical evidence.

In my (poor) understanding, Einstein's Theory is an observational Theory, I mean it is a Theory in which an observational crucial element -C- has been inserted, and as a matter of consequence, all observations will always confirm the Theory. It is the snake who eats his own tail.
So IMVHO it is an excellent Theory for describing what any observator will observe but not necessarily a Theory that depicts what really happens. Unless one consider that what we observe is identical to what happens.

I see you have expanded this post. I would agree with everything here but I would say that your understanding ot the theory is wrong. Your understanding of Einsteins intentions are wrong. And in fact, and in admittance of my own shortcomings, realities has proven at least some aspects of the actual STR, without really explaining what causes them.

Or perhaps more in my (our?) favour, Einsteins assumptions are wrong, but his measurements are rock solid.

 

 

Unless one consider that what we observe is identical to what happens.

 

This what I understand many people sadly do with the theory.

[xyzt]

 

I see you have expanded this post. I would agree with everything here but I would say that your understanding ot the theory is wrong. Your understanding of Einsteins intentions are wrong. And in fact, and in admittance of my own shortcomings, realities has proven at least some aspects of the actual STR, without really explaining what causes them.

 

Or perhaps more in my (our?) favour, Einsteins assumptions are wrong, but his measurements are rock solid.

 

This what I understand many people sadly do with the theory.

Or your fixation with "Einstein was wrong" is clouding your thinking?

[Myuncle]

Questionist, it looks like you are frustrated like me when I started this thread 5 years ago. After 5 years, I am less frustrated, I mean, I still think that the Relativity is not well written and not well explained, and that there are things that don't make any sense (time is not a dimension, it's just a sequence of movements). But at least I am happy to have understood (or at least I am convinced to have understood...) that there is substance in the theory. This substance can be explained in a few words: gravity bends the light (see eclipse 1919, in the photos the stars behind the sun changed position), and I understood that a combination of gravity and speed, alter the state of clocks, bodies, or any subatomic particle. Lack of gravity accelerates the clocks, and speed (of a travelling satellite etc) decelerates the clocks. This is why clocks on a satellite give a different reading than clocks on the ground. And this is why an atomic clock upstairs is slightly ahead of an atomic clock downstairs. After 5 years I learnt that our GPS still relies on this theory. So, big deal?...you might think? Yes, it's a big deal, and if Einstein was the first one to discover it and calculate it, he deserves all the credit. Hope this helps you Questionist, you and all the common mortals like me, who thought Relativity was just rubbish.

[Strange]

I am glad you have managed to come to some sort of resolution of your doubts.

 

... there are things that don't make any sense (time is not a dimension, it's just a sequence of movements)

 

On this specific point, I know there are people (including very serious philosophers of science) who think that time might not be "real" in some deeper sense (whatever that means). But you cannot get away from the fact that, even in everyday life, time is a dimension. If you want to organize an event (e.g. to meet someone) you need to specify 4 independent coordinates: 3 spatial ("where") and 1 temporal ("when"). This is nothing to do with relativity. Even if you think time is just movement (*) or a psychological artefact, you can't get away from that fact about the world we live in.

 

(*) This is trivially wrong, but that has been thrashed out in thousands of posts in dozens of other threads so lets not discuss it here.

[Myuncle]

I am glad you have managed to come to some sort of resolution of your doubts.

 

 

On this specific point, I know there are people (including very serious philosophers of science) who think that time might not be "real" in some deeper sense (whatever that means). But you cannot get away from the fact that, even in everyday life, time is a dimension. If you want to organize an event (e.g. to meet someone) you need to specify 4 independent coordinates: 3 spatial ("where") and 1 temporal ("when"). This is nothing to do with relativity. Even if you think time is just movement (*) or a psychological artefact, you can't get away from that fact about the world we live in.

 

(*) This is trivially wrong, but that has been thrashed out in thousands of posts in dozens of other threads so lets not discuss it here.

 

Thanks Strange. If you want to organize an event you don't need time, you just use time as tool. You don't need a when, but it would be better to say that you use a when, just to keep track and calculate the movements. There are many sequences that we can calculate and measure, time is just one of this sequence. But I agree that we can discuss this in other threads .

[StringJunky]

 

Thanks Strange. If you want to organize an event you don't need time, you just use time as tool. You don't need a when, but it would be better to say that you use a when, just to keep track and calculate the movements. There are many sequences that we can calculate and measure, time is just one of this sequence. But I agree that we can discuss this in other threads .

Two massive objects cannot occupy the same space at the same time, but they can at different times, therefore, time is not just a tool.

[Myuncle]

Two massive objects cannot occupy the same space at the same time, but they can at different times, therefore, time is not just a tool.

Two objetcs cannot occupy the same space because they collide with each other, no matter when. Again, space is needed, time is not needed. I never said that time is only a tool, I say that time is 1) a sequence of movements, 2) a meausuring tool, 3) a human idea.

[ajb]

Two objetcs cannot occupy the same space because they collide with each other, no matter when.

Quantum mechanics starts to make this even less clear, but anyway we can stick to classical stuff here.

 

I never said that time is only a tool, I say that time is 1) a sequence of movements, 2) a meausuring tool, 3) a human idea.

How is this fundamentally different to the concept of length as a measuring tool (we assign some units to length) and a human idea?

[StringJunky]

Two objetcs cannot occupy the same space because they collide with each other, no matter when.

So, if massive object A passes through xyz at t=1 and massive object B passes through xyz at t=2, they will collide?

[ajb]

So, if massive object A passes through xyz at t=1 and massive object B passes through xyz at t=2, they will collide?

I think he considers on object to be fixed and then for all time you cannot place another object at the same location as the first object. Rather than fix a location...