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

[Serena2003]

Two assumptions considered in special relativity:

 

-Laws of Physics remain the same for all observers

 

-Speed of light is constant regardless of the motions of light source and observer.

 

 

When considering two observers in an environment without acceleration and deceleration, all gravity, mechanics and the speed of light would be experienced the same. Two events may look concurrent to one observer, but to the other, the measure of time may feel completely stretched or enduring. When two observers are in relative motion together, the peculiar effect is called "relativity of simultaneity." This may seem insignificant in reality, but depending on an object relative speed, it becomes more evident. Clocks in accordance to "time dilation" may be measured more slowly than and observer's stationary clock.

 

E=MC2 pertains to the mass-energy equivalence which means nothing can move faster than the speed of light. Both energy and mass are interchangeable and conserved energy would increase an object's mass. Time is dependent on the relative motion of the observer who is measuring time.

 

General relativity is meant to define the topology of spacetime and the inertia of objects with a metric theory of gravitation. It measures the effects an object's movements without any force pushed upon it in which the acceleration and gravitational field are the same. "Gravitational time dilation" is a consequence of slowed time when gravity is more dense.

 

An understanding of the appropriate level of math may give you a more accurate understanding, but really it is all about the intimate relationship between time and space and that they can be stretched, warped and exchanged.

[Myuncle]

Two assumptions considered in special relativity:

 

-Laws of Physics remain the same for all observers

 

-Speed of light is constant regardless of the motions of light source and observer.

 

 

When considering two observers in an environment without acceleration and deceleration, all gravity, mechanics and the speed of light would be experienced the same. Two events may look concurrent to one observer, but to the other, the measure of time may feel completely stretched or enduring. When two observers are in relative motion together, the peculiar effect is called "relativity of simultaneity." This may seem insignificant in reality, but depending on an object relative speed, it becomes more evident. Clocks in accordance to "time dilation" may be measured more slowly than and observer's stationary clock.

 

E=MC2 pertains to the mass-energy equivalence which means nothing can move faster than the speed of light. Both energy and mass are interchangeable and conserved energy would increase an object's mass. Time is dependent on the relative motion of the observer who is measuring time.

 

General relativity is meant to define the topology of spacetime and the inertia of objects with a metric theory of gravitation. It measures the effects an object's movements without any force pushed upon it in which the acceleration and gravitational field are the same. "Gravitational time dilation" is a consequence of slowed time when gravity is more dense.

 

An understanding of the appropriate level of math may give you a more accurate understanding, but really it is all about the intimate relationship between time and space and that they can be stretched, warped and exchanged.

 

Thanks Serena, but you see, I find it difficult to understand for example the twin paradox, and to understand what Einstein said that others didn't before him, here is my rant...

Travelling clocks: the quality of the original results has been criticized in 1996 by A. G. Kelly, and Louis Essen (the inventor of the atomic clock) in 1988 in which he discussed the inadequate accuracy of the previous experiments. Also one thing is a clock, another thing is human travelling near speed of light, all the opposite could happen: wrinkled skin, failing organs, weaker immune system, etc.

Mercury's orbit: why don't we go back and give more credit to Le Verrier? In 1859, Le Verrier was the first to report that the slow precession of Mercury’s orbit around the Sun could not be completely explained by Newtonian mechanics and perturbations by the known planets. He suggested, among possible explanations, that another planet (or perhaps, instead, a series of smaller 'corpuscules') might exist in an orbit even closer to the Sun than that of Mercury, to account for this perturbation.

Lasers: why don't we talk about Townes and Schawlow? In 1954 Charles Townes and Arthur Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation - the maser was invented before the (optical) laser. The technology is very close but does not use a visible light.

Gravitational lensing: Orest Chwolson is credited as being the first to discuss the effect in print in 1924, the effect is more commonly associated with Einstein (wonder why...), who published a more famous article on the subject in 1936.

The speed of light: is constant, fair enough, but Ole Rømer first demonstrated that it travelled at a finite speed in the 17th century, I find it much more fascinating than Einstein, that's all I need to know, all the other examples about the twin or two astronauts in space make no sense to my limited intelligence. Things change of course when travelling near speed of light, but no man has ever travelled at that speed, not even ants.

It looks like Einstein has been pumped up by the media, he has been accredited for things he didn't do at all.

Sometimes I think that kids are much better scientists, you can't fool them, they have less prejudices than adults, if something doesn't make sense to them they don't hesitate to show it to you. If you try explaining the relativity to 10 years old kids they probably are going to suggest that this makes no sense, you can keep talking about examples of the twins, and they will tell you that it doesn't make sense to them. But if you explain Darwin, Edison or Newton the kids understand it pretty well and feel even excited about it.

Just my modest view, not because I hate Einstein, but just because I am interested in the truth and nothing but the truth, and sorry for the rant

[Serena2003]

The paradox is suppose to exemplify that one twin has undergone acceleration and deceleration while the other is stationed in an inertial environment which differentiates both cases. It may not make much sense, but hence why it is called a paradox. But the paradox has been used to accurately measure clocks in airplanes.

 

Like Darwin who was not the first to speculate evolution, Einstein may not have been the first to speculate relativity. However, he is considered to be the one who proved it. Whether or not the credit for his works was just stimulated by the media is beyond me, but as far as we know it was not. The truth is something we would all like a piece of, but even after all we have accomplished and discovered, we are still no where near it.

[Paul Murphy]

Myuncle,

 

There are a few really good examples of time dilation. One example is Muons decaying more slowly than they should as they fall through our atmosphere at .994 of the speed of light. Also, GPS would accumulate errors and be off by almost a mile within 24 hours if relativistic time effects weren't corrected for (both the satellite motion and the gravitational considerations due to time dilation). These experiments and many others lead me to believe that relativity is describing what happens in reality. If you really do want to understand relativity, my recommendation is to try the Teaching Company lectures taught by Wolfson or make a short list of specifically what you're not understanding about relativity and someone here on the forums will do their best to make a clear explanation. Brian Greene's book, The Fabric of the Cosmos, also has a great explanation about the relativity of simultaneity. It goes something like this...

 

Imaging drawing a cartoon of a duel on transparency slides with two people shooting at each other. Each page of transparency would be an interval of time and you would stack them in an ever growing pile until the made a cube. The trajectory of the bullet would be a line in 3D space. Now, imagine tilting the entire cube at a certain angle and slice trough it, layer by layer. You will intersect the lines at different times based on the angle your slices are being cut at. Also, if you are accelerating as you slice, the slice will have a curve and you'll have different results again.

 

I don't know if your Barnes and Noble will have it, but the ones by me have Leonard Suskind's, The Black Hole War, for about $5 in hardcover on the bargain books shelves. His writing is very clear and I'd recommend that book as well. They also have the double-volume illustrated Hawking books, but I think they are $15. Still worth it, in my opinion.

 

I know I'm new here and I won't be able to help much until I become more educated, but my advice stands. If you honestly want to understand rather than debunk, I'm sure you'll get a lot of help here.

Edited September 6, 2010 by Paul Murphy

[swansont]

Speed of light is constant, ok, what does the Relativity has to add to that? I find it hard to believe that after so many years there are so many people (including me..) that don't understand this theory, I mean are we all so stupid and just a few genius can afford to understand it? And yet if I read a simplyfied explanation I always find it doesn't make sense...

 

I'll reiterate: our common experience is Newtonian physics and Galilean transforms. People have similar responses to quantum mechanics — it's just weird in comparison to classical physics. But that doesn't make it wrong.

 

Thanks Serena, but you see, I find it difficult to understand for example the twin paradox, and to understand what Einstein said that others didn't before him, here is my rant...

Travelling clocks: the quality of the original results has been criticized in 1996 by A. G. Kelly, and Louis Essen (the inventor of the atomic clock) in 1988 in which he discussed the inadequate accuracy of the previous experiments. Also one thing is a clock, another thing is human travelling near speed of light, all the opposite could happen: wrinkled skin, failing organs, weaker immune system, etc.

 

From what I recall of Kelley's criticism, it boils down to him not understanding timekeeping. Clocks measure time, so no, the opposite won't happen, if the effects are due to the passage of time.

 

Lasers: why don't we talk about Townes and Schawlow? In 1954 Charles Townes and Arthur Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation - the maser was invented before the (optical) laser. The technology is very close but does not use a visible light.

 

I doubt most people have ever seen a maser, whereas lasers are ubiquitous. People see them in action every time they go to the store and they might be aware that the own one or two in their CD and DVD players.

 

 

Most of your objections are related to the teaching of science history rather than the science itself. Yes, they are fascinating topics, but in the finite amount of class time available to learning physics in a class devoted to learning physics, they are pretty much irrelevant.

[Myuncle]

Myuncle,

 

Imaging drawing a cartoon of a duel on transparency slides with two people shooting at each other. Each page of transparency would be an interval of time and you would stack them in an ever growing pile until the made a cube. The trajectory of the bullet would be a line in 3D space. Now, imagine tilting the entire cube at a certain angle and slice trough it, layer by layer. You will intersect the lines at different times based on the angle your slices are being cut at. Also, if you are accelerating as you slice, the slice will have a curve and you'll have different results again.

 

Thanks Paul, I tried already with these kind of examples, they make you go like " Oh yes, now I understand it !", but they just give me the illusion that it makes sense, I prefer to be more realistic and think that I am not clever enough rather than pretending to understand.

[Severian]

I will go with option A.

[lemur]

Why didn't anyone build an atomic bomb or nuclear reactor before Einstein came up with the equation?

 

To use mass conversion as the source of energy for the explosion, one needs to know that mass is a form of energy, and can be converted to other forms. Without that concept, nobody would bother pursuing it.

 

Maybe the only reason anyone developed such a bomb is because they were afraid of the consequences of what it would mean for people to have access to unlimited energy. The fact that people react to power with fear and the desire to control power is not reason to blame the messenger. While some people reacted to the prospect of infinite energy with fear, others saw it as a road to peace and prosperity. If that ideology had dominated the reception of Einstein's claim, why would they have developed bombs instead of nuclear power plants?

 

BTW, do you really find it legitimate to blame use of a technology on its inventors or developers? Do you think Karl Daimler or Henry Ford is responsible for all the deaths, injuries, and health problems caused by driving each year globally?

[katabana]

i only have very, very, very basic knowledge on relativity, so i hope i'm posting in the right place..

 

i've read that the watch an observer that is closer to a sun runs slower than the observer that is further from the sun and 1st observer due to their perception of time/space, and the 1st observer actually age slower than the 2nd observer, correct?

 

can i assume that two perfectly synchronised, perfectly conditioned watch will run with different speed because of their distance from gravity? or does the "time" that i've read refering to our biological clock, and both watches will still run in perfect synchronisation?

[Klaynos]

The perfect clocks will run differently.

[swansont]

Maybe the only reason anyone developed such a bomb is because they were afraid of the consequences of what it would mean for people to have access to unlimited energy. The fact that people react to power with fear and the desire to control power is not reason to blame the messenger. While some people reacted to the prospect of infinite energy with fear, others saw it as a road to peace and prosperity. If that ideology had dominated the reception of Einstein's claim, why would they have developed bombs instead of nuclear power plants?

 

BTW, do you really find it legitimate to blame use of a technology on its inventors or developers? Do you think Karl Daimler or Henry Ford is responsible for all the deaths, injuries, and health problems caused by driving each year globally?

 

I'm not sure how you got here from what I said. I did not blame Einstein for anything, nor was I discussing politics/ideology. I was simply pointing out that one would not investigate mass as an energy source if one did not know mass was a form of energy.

[Myuncle]

I was simply pointing out that one would not investigate mass as an energy source if one did not know mass was a form of energy.

 

After the discovery of radioactivity in 1897 it was well known that the total energy due to radioactive processes is about one million times greater than that involved in any known molecular change. The existence of a huge amount of latent energy, stored within matter, was proposed by Ernest Rutherford and Frederick Soddy in 1903. Rutherford also suggested that this internal energy is stored within normal matter as well.

[swansont]

After the discovery of radioactivity in 1897 it was well known that the total energy due to radioactive processes is about one million times greater than that involved in any known molecular change. The existence of a huge amount of latent energy, stored within matter, was proposed by Ernest Rutherford and Frederick Soddy in 1903. Rutherford also suggested that this internal energy is stored within normal matter as well.

 

And without Einstein's contribution, undoubtedly someone else would have made the discovery that mass was a form of energy, because of the experimental evidence that was accumulating. But AFAIK nobody was looking to build a reactor or bomb, using this principle, prior to the early 1900s. Even after relativity, it took the discovery of the neutron to point in that direction. Many of the discoveries along this path are inter-related, of course.

[lemur]

And without Einstein's contribution, undoubtedly someone else would have made the discovery that mass was a form of energy, because of the experimental evidence that was accumulating. But AFAIK nobody was looking to build a reactor or bomb, using this principle, prior to the early 1900s. Even after relativity, it took the discovery of the neutron to point in that direction. Many of the discoveries along this path are inter-related, of course.

 

You're still implying that the conditions of a technological development are at least partly responsible for the usage/application of the technology in practice. What you are basically saying is that without the scientific and technological developments that were conditions for developing atomic weaponry, that weaponry couldn't have been deployed. But you could say the exact same thing about the conditions of nationalism and war that culminated in the ability to exact wholesale slaughter against a regional population without regard for the individuality of victims separately. So you're basically attributing nuclear holocaust to the scientific and technological conditions without paying any attention to the political and social conditions. Furthermore, please note that other mass killing went on during the same time and previously in history without the use of nuclear technology. So the physics may have changed the tool, but it didn't create the project the tool was used for. Would you blame physicists for the use of the guillotine or electric chair? Would you blame biologists for biological weapons or chemists for chemical ones?

[swansont]

You're still implying that the conditions of a technological development are at least partly responsible for the usage/application of the technology in practice.

 

I don't think I am, and in any event, that is not my intent.

[Sisyphus]

lemur, I don't think anyone is blaming Einstein for nuclear holocaust.

[lemur]

I don't think I am, and in any event, that is not my intent.

 

Then what are you saying exactly about the relationship between Einstein, E=MC^2, and the emergence of atomic weaponry?

[swansont]

Then what are you saying exactly about the relationship between Einstein, E=MC^2, and the emergence of atomic weaponry?

 

That if there were no knowledge of E=mc^2, one would not have been investigating these interactions as an energy source, contrary to the "Einstein is overblown" position of the OP. I don't think I've stated any position regarding the "goodness" or "badness" of the results, in this thread.

[between3and26characterslon]

Why anytime I ask explanations about it I hear always the same excuses "if I don't understand it's because it's too complicated...blah blah". Why nobody can explain Einstein easily or simply? There is nothing difficult in this world if someone explain it properly. This theory sounds like useless bombast. I haven't seen any fact yet, not a single acceptable proof. There is nothing to understand because there is no substance, just castles in the air. Nothing of what he said has been clearly proven. All we got now it's not because of Einstein: computers, rockets, fridges, televisions, robots, electricity, cars, radio. Why everybody understand Darwin, Marconi, Newton? Because they said clever things with substance. In Einstein I see no substance. Did we go to the moon thanks to Einstein?

 

 

Ok to get back to your question I will try to explain it simply.

 

First of all we need to go back to Galileo who suggested 'The Principle of Relativity'. The principle of relativity says that whatever laws of nature are true for one observer they must also be true and the same for another observer. The laws in one system of coordinates must be no less simple in another system of coordinates.

 

It also said that all observers are in motion relative to something, that is to say NOTHING is absolutely at rest. If something was absolutley at rest then every observer would be in motion relative to it. That means an observer would have to take into account their motion when formulating their laws of physics.

 

An example; when I drop a ball I see it fall straight to the ground. If I was on a moving train and I dropped a ball I would also see it fall straight to the ground (floor of the train) If the principle of relativity was not true I would have to take into account the motion of the train when describing how the ball falls. This means the laws of physics on the train would be different to those on the ground outside.

 

to clarify, the principle of relativity is

 

1) Objects or observers can be at rest with respect to each other but nothing is absolutely at rest.

2) All objects or observers are in motion with respect to something.

3) The laws of physics for one observer must be the same and no less simple for another observer.

 

What did Einstien do?

 

He realised that if the laws of physics state that the speed of light in vacuo is constant then it must be constant for every observer regardless of how they are moving. But how can that be?

 

If I am standing on a platform at a train station and a train shoots past at some enormous speed and a beam of light is fired in the direction the train is travelling then I on the platform measure the speed of light to be c (3x10^8 meters per second). Also the person on the train measures the speed of this light beam to be c, he does not add or subtract his speed from the speed of light because the speed of light in vacuo must be constant for all observers regardless of how they are moving.

 

If you accept Galileo's principle of relativity is true and that both observers measure the speed of light to be the same something doesn't make sense.

 

So how can it be that if I'm stationary relative to the source of light and another observer is moving with incredible speed in the same direction as the beam of light we both measure the light to be travelling at the same speed relative to us.

 

The theory (Einstein's) is that on the train time has slowed down relative to the observer on the platform and distance (in the direction the train is moving) has got less relative the the observer on the platform. This means when the light gets to the observer on the train it has less distance to travel because the train is shorter and has more time to do it in because time has slowed down.

 

The observer on the train does not notice that his time is slower or his length is less, to him nothing has changed. Exactly the same laws of physics apply to him moving at speed as apply to the observer on the platform who is stationary (relative to the light source)

 

The principle of relativity is preserved and the speed of light is preserved for both observers but there is a transformation form one observer to the other. The laws of physics that describe the transformation of time and length of one observer as viewed by the other observer are the same for both observers viewing each other and are no less simple as per the principle of relativity.

 

Hope that makes sense.

[TrueHeart]

Why nobody can explain Einstein easily or simply?

Relativity is all about how light behaves, and from that some truth is differentiated from some fiction. Light's behavior is particularly at issue because the cosmos is ever expanding… some of the very distant galaxies are receding from us at near light speed — we find that true while looking in every direction.

 

Getting right into it, if a fleet ("The Fleet") of spacecraft left Earth and sped away at a significant fraction of lightspeed, then how would light (and/or radio, EM) signals behave between us and them? and how would such signals behave among The Fleet members themselves?

 

Would a radio signal sent from Earth take extra time to reach The Fleet, because it is receding away? Yet the reverse is not true?? ie. signals from The Fleet will transit only the predetermined distance through Earth's fixed coordinate system? Who is actually receding from whom?? Does it depend on how Earth is moving with respect to a higher coordinate system, some fixed master coordinate system?

 

In a word no, none of that is true. OK it's all true, relatively true. What's absolutely true is the denial of any master cosmic framework serving as medium for electromagnetic signal transmissions: EM signals find their own way about, somehow transcendent of mortal ciphering. It's uncanny; we don't know the how but we know the how much. We realize now that light behaves relativistically, which means that every clock and every ruler in the world must cede something to accommodate the feat.

 

In the stated scenario, The Fleet astronauts experience one thing while us Earthbound folk experience something altogether different, something that seems contradictory. By all reckoning, the astronauts witness EM signals to be moving at fixed lightspeed with respect to The Fleet's native 3D coordinate system — and by native is meant simply, "that x-y-z frame with respect to which The Fleet is stock still in space." Those astronauts… they witness their outgoing signals as requiring extra time to "catch up" to the receding Earth, yet incoming Earth signals need only travel the predetermined distance from their release point. And all the calculations work out… no, there is no incompetence.

 

And wouldn't you know? Earthlings can make the very same claim. By all reckoning, they witness EM signals behaving as if Earth's native 3D coordinate system is boss. Their outgoing signals require extra time to catch up to the receding space Fleet, yet incoming Fleet signals need only travel the predetermined distance from their release point.

 

And this relativity carries over to within The Fleet itself: its member craft are able to swap messages among themselves, with only their fixed separation distance dictating the transmission delay. Light and radio signals don't take longer to transit in one particular direction because of The Fleet's supposed motion "through space" — that element is negated entirely.

 

And now the final concluding point. Isn't it great that light behaves this way? especially considering that many millions of distant galaxies are flying away from us at tremendous speeds. If light simply moved relative to Earth, or relative to some master cosmic coordinate system (with respect to which Earth is fairly still), then how could those (hypothetical) zillions of aliens who populate those myriad distant galaxies ever live, eh?? they couldn't!! They would live in a giant ever-distorted world, where a simple twisting of the neck would mean drastic changes in their view of the surroundings — all hot and blue-shifted in one direction, pale and red-shifted in the other. They could be burned alive by a single candle flame if its radiations were coming from the wrong side.

[Myuncle]

I believe in the future stem cells will cure everything and stop the aging process, and I also think that any mammal travelling at high speed would be affected by failing organs and a weaker immune system (just my opinion).

So, two people of the same age are on Earth. They are identical twins, twin A and twin B, they are 20 years old. Twin A boards a spaceship and begins to travel near the speed of light, Twin B remains on earth. 40 years later Twin B, still on earth is now 60 years old but thanks to stem cells he looks and functions still like a 20 years old. Twin A has just returned to Earth and (unless he died in the first few hours) he looks much older than Twin A because he didn't take any stem cells.

Any thought on this?

Thanks.

[swansont]

I believe in the future stem cells will cure everything and stop the aging process, and I also think that any mammal travelling at high speed would be affected by failing organs and a weaker immune system (just my opinion).

So, two people of the same age are on Earth. They are identical twins, twin A and twin B, they are 20 years old. Twin A boards a spaceship and begins to travel near the speed of light, Twin B remains on earth. 40 years later Twin B, still on earth is now 60 years old but thanks to stem cells he looks and functions still like a 20 years old. Twin A has just returned to Earth and (unless he died in the first few hours) he looks much older than Twin A because he didn't take any stem cells.

Any thought on this?

Thanks.

 

My thought is that it is not really about relativity.

[Craig Dilworth]

Why anytime I ask explanations about it I hear always the same excuses "if I don't understand it's because it's too complicated...blah blah". Why nobody can explain Einstein easily or simply? There is nothing difficult in this world if someone explain it properly. This theory sounds like useless bombast. I haven't seen any fact yet, not a single acceptable proof. There is nothing to understand because there is no substance, just castles in the air. Nothing of what he said has been clearly proven. All we got now it's not because of Einstein: computers, rockets, fridges, televisions, robots, electricity, cars, radio. Why everybody understand Darwin, Marconi, Newton? Because they said clever things with substance. In Einstein I see no substance. Did we go to the moon thanks to Einstein?

 

 

You're quite right. I've written a paper undermining the theory. (Why do you think Einstein sticks his tongue out on that famous photograph?) I don't want to publish the paper here, so if you're interested and give me your email or think of some other way we might contact privately, I'll send you a copy.

 

Craig

 

I'd argue that plenty of people don't understand Darwin, Marconi and Newton.

 

Anyway, lasers are a result of Einstein's work, which (as Klaynos has mentioned) enables the internet.

 

 

Yes Swanson, but a result of his photon theory, not special relativity. The 'experimental results' of the special theory do not differ from those of the Maxwell-Lorentz theory.

 

Craig

[michel123456]

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.

Edited December 5, 2010 by michel123456

[IM Egdall]

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.

 

 

A little history:

 

Before Einstein

Galileo's dictum in effect said that there is no way to tell internally whether you are in uniform motion or at rest. Uniform motion is relative. Physicists used the so-called Galilean transform equation to go from at rest to moving uniformly. Newton's laws of motion obeyed Galileo's dictum but Maxwell's equations of electromagnetism did not! In other words, Maxwell's equations were different for inside a moving vehicle than for inside one at rest. This impied that electromagnetism behaves differently when a vehicle is moving uniformly. This, of course, is not true. This was a great puzzle to physicists.

After Einstein

 

Einstein came along in 1905 and proposed that light always travels at the same speed (in vacuum), regardless of the motion of the source of that light or the motion of any observer. From this absolute speed of light postulate, Einstein then came up with a new transformation equation for relative motion. It showed that Maxwell's equations now do obey Galileo's dictum. It also meant that Newton's laws of motion had to modified when speeds approach the speed of light.

 

Einstein didn't know at the time that his new transform equation had already been developed by Lorentz (and others). So it is called the Lorentz transform. (But Lorentz did not understand its full physical significance.) The point is that Einstein took Galileo's dictum on relative motion and extended it to electromagnetism. Einstein then declared that Galileo's dictum applies to all physical phenomena. So Einstein took Galileo's dictum and made it a universal law.

 

And yes, all of special relativity comes from Einstein's light postulate. Reportedly, Einstein did not like the name "relativity" for his theory. He preferred it be called "invariance" theory, because the speed of light does not vary.