## JerryP Group Title What is the root cause of relativity? one year ago one year ago

1. UnkleRhaukus

spacetime

2. Mashy

the nature just works that way.. its almost as if at the time of big bang, something was decided.. and that something was the speed of light c.. it was decided that regardless of what happens, the speed of light in our universe in vacuum will always be c.. maybe its like a unique identity given to all the universes... so that we can distinguish one universe from another!!.. just a theory :D

3. JerryP

If that’s true, then what’s the root cause of space-time?

4. UnkleRhaukus

expansion

5. gleem

"The more the universe seems comprehensible, the more it also seems pointless" Steven Weinberg Do you get it?

6. karenraymond

I guess everything is wrapped up in space n time..!:D And you really can't separate time and space!

7. TuringTest

I would add, spacetime + the non-relative character of the speed of light

8. gleem

Time is intertwined with change in position which allows us to distinguish between events and in fact defines events. Does time exist without matter? does space exit without matter?

9. JerryP

Do you believe that structures can be dimensionless? That is an object that can not be referenced in any way; as contrasted to a point, though dimensionless, that may be referenced by it coordinates in space. If you do, how could you substantiate its existence?

10. gleem

I don't understand your point.

11. tigger12many

space and time!

12. Iamgmg90

The relationship between space and time with a constant of SQRT(1-(v^2/c^2)). & the relationship between energy and matter with a constant c^2. Where c = 299 792 458 m/s

13. Jemurray3

Special relativity relies on the following postulates: (1) The speed of light in vacuum is a finite constant, independent of reference frame and (2) The laws of physics are the same in all inertial reference frames. I think that the fundamental question you're trying to get at is "Why do things behave in such strange ways at high speed, in a few (comprehensible) sentences?" The answer to that question is that when we observe the world around us we are used to associating an event with the time that we see it -- for instance, if you see somebody drop a coffee cup, you say "aha, you have just now dropped your cup!" In reality, though, the more precise statement is "aha, the light from your dropped cup has just now reached my eyes!" These two statements are fundamentally different because the first associates an event with your observation without referencing the fact that you were not influenced by the cup, but rather by the light coming from the cup. In other words, you form a link from the cup to your eyes and think nothing more of it. However, the second (correct) statement links the cup to the light, then the light to your eyes. Because light travels so very quickly, in everyday experience these two ways of understanding your observation are, for all intents and purposes, equivalent, because the light takes effectively no time at all to reach your eyes. However, when moving with speed comparable to that of the speed of light, moving towards or away from the cup as it falls can significantly change what you perceive. Hopefully that wasn't too long and drawn out. The short answer is "Because light travels at a constant, finite speed".

14. JerryP

Everyone has provided very good responses so far, but not the final answer I am looking for; i.e. one root cause for general or specific relativity.

15. Mashy

Like i said.. my view is that when the universe was created.. something about it was SET... a constant was set.. and that constant turns out to be C the speed of light in vacuum.. cause to make laws of nature, it must be in reference with something... so in our universe all laws are built by taking that reference.. that whatever happens, you ll never see light going in vacuum at any speed other than c, regardless of what you do ..

16. Iamgmg90

Relativity is understood by very few, I don't fully understand it and I've studied it for a year. An explanation cannot be given in English alone, Jemurray3 gave the best response you'll get.

17. Mashy

i believe the true question is why is the speed of light a constant.. !??

18. Iamgmg90

its not really, well, it is, in a vacuum. It travels different speeds in different mediums. The electromagnetic spectrum is the bigger picture that's to be looked at. speed of wave = frequency x wavelength. Ultra-violet, Infrared, Microwaves, Gamma waves. Wave-particle duality, quantum mechanics, light isn't something we understand fully either, we know have deduced how it behaves in situations. What question are you asking.

19. Mashy

m talking about its speed in vacuum itself :P.. its a constant regardless of which frame of reference you are in.. thats not true with anything else!! its like all the laws of nature are just made to make sure C remains a constant!!

20. Jemurray3

This might be kind of confusing, but think of it this way... the fact is that there is a maximum speed limit for objects traveling through space. That is a fundamental property of the universe. It also happens that no object that has this peculiar property called "mass" can ever be accelerated to reach this speed -- so only massless objects can ever move with this enormous velocity. We call it the speed of light because light is the only common and well-understood thing that moves through space without having to deal with mass. It travels at this enormous rate but for no reason other than the fact that light is massless. @JerryP Special (not specific) relativity is the correct theory of space and time, linking them together into a 4-dimensional arena called spacetime. If you allow for light to travel at finite speed regardless of the motion of the observer, then the rest of special relativity follows but the mathematics can get complicated so if you're searching for a trivially easy explanation of its details I think you're fighting a losing battle. General relativity is the extension of special relativity that describes gravity as warps and curves in the normally nice, flat spacetime. Any understanding beyond that will require deep and advanced mathematics, I'm afraid. Far deeper than is required to adequately understand special relativity.

21. JerryP

Jemurray3 All your points are good. I have the following questions: Does special (or specific) relativity exist without mathematics? If no, then what in mathematics is essential to their definitions? If light is massless then how can it be affected by gravity; i.e. black holes? If I understand correctly, as objects approach the speed of light their mass increases infinitely, except for light and neutrinos. Finally, I am confused by the use of velocity to describe its speed. After all we don’t really see light, we only see the artifacts of the intersections of its waves, no?

22. Jemurray3

It is special, not specific. Your first question is not particularly meaningful. We describe physical reality through mathematics, but I don't know what you mean by asking "does relativity exist without it". Photons and gravity: According to general relativity, mass and energy cause the fabric of spacetime to be warped and curved. All objects then move along those curves, the result being an apparent attraction to one another. Although light does not have mass, it still must travel through this warped space, and therefore strong gravitational fields will bend the path of the light. Increasing mass: In the old days, people said that mass was a function of velocity and that it increases as one approaches the speed of light. Nowadays we change our terminology a bit, and we say that the mass of an object is constant but its momentum approaches infinity as its velocity approaches the speed of light. This is a better way to look at it for a number of reasons. Neutrinos do in fact have mass so the same thing applies, but their masses are extremely small. Lastly, when we speak of the speed of light, we mean the velocity with which the light waves propagate in space. If you throw a rock in a pond, the circular waves travel outward from the splash at some speed -- in a similar way, light waves travel through space at the constant speed c = 300,000,000 meters per second.

23. JerryP

Thanks for clearing this up, I get it now - It is special, not specific. As for "does relativity exist without it [mathematics]", what I am asking is can you separate reality from mathematics? Or, put another way; do you believe that you can map all of relativity to mathematics? For instance, where is zero? Can you step outside and point to it? Is it not a pure mathematical construct? On your Increasing mass point I’m confused. I thought the speed of light [c] has the following relationship with mass: $p=m*v$ (where p is the momentum, m is the mass and v is the velocity) Finally, on your point about Photons and gravity: yes, I agree that that it widely held today that strong gravitational fields will bend the path of the light but I asked about black holes, where light is just not bent, but is demolished. Again, if light is massless then how can it be affected by gravity like this? Also if it’s massless the above formula would be a constant zero; meaning that the momentum would be zero. You express yourself very well, I appreciate your efforts. Thanks :) JerryP

24. Jemurray3

The first point still doesn't make sense to me. Perhaps it is because you have a different idea of what mathematics is. We all have the ability to think logically and analyze reality quantitatively -- You may count banana slices when making breakfast, or deduce that you should fill up your gas tank because your fuel gauge is close to empty. This is what mathematics is, in its infancy. When you're planning a road trip and need to budget for travel expenses, the calculations aren't as simple as adding banana slices or reading a gauge so its helpful to use a calculator or a pen and paper -- but this is no more mathematical, only more complicated. When you describe a ball bouncing up and down, the same ideas apply. Its true that the methods of calculation have become more abstracted (algebra is more abstract than arithmetic), but it is yet again no more mathematical. The tools you have developed are more advanced and generally applicable to many different situations, but the fundamental heart and soul of what your doing is the same. And finally, when you discuss the motion of a particle with tremendously high speeds and describe it using special relativity, although the mathematics is yet more advanced than algebra, at the end of the day it's all counting banana slices. So when you ask me whether relativity "exists" outside of mathematics, I am confused. Relativity isn't something that 'exists' or 'doesn't exist', it is just a more accurate description of the world than we had before. I don't understand what you mean when you ask if something can exist outside of your way of describing it. It seems like a nonsensical question.

25. Jemurray3

As to your other point -- no, that is not true. Momentum obeys this relationship: $\vec{p} = \frac{ m\vec{v}}{\sqrt{1- v^2/c^2}}$ if v<<c, then the denominator is basically equal to 1 -- so your relationship is true. That is the relationship that we used in nonrelativistic physics because it's easier to use, but it's only an approximation that is valid for small velocities. As for the part about the mass being zero -- the true relationship between energy and momentum for an object is $E^2 = m^2c^4 + p^2 c^2$ You'll notice that in our above equation for momentum, if m = 0 but v = c then we have an undefined quantity. That way of describing momentum is true only for massive particles -- it is inadequate for describing the momentum of massless photons. Notice from the energy-momentum relationship above that if m = 0, $p = \frac{E}{c}$ is the momentum of the photon. Using this, it is possible to recover the equation for radiation pressure that was originally established using the model of light where it travels as a wave rather than a discrete photon -- an example of the fact that multiple ways of looking at a phenomenon are not necessarily mutually exclusive if they make the same predictions. Finally, in a black hole light is not 'demolished'. A black hole is a region of space where the gravity is so strong that the warps and curves in space essentially loop back on themselves. In that case, photons traveling along those curves would never leave the black hole, you see?

26. JerryP

Jemurray3, I cannot find your formulas. Would you provide links, Wikipedia or such, to them? Thanks - JerryP

27. Jemurray3