# Speed of Light: Exploring Special Relativity

• Arens
In summary: This is incorrect:... Now if our particle is seen from many infinite point reference points, it travel with infinite speed.This is correct:... If universe is infinite than distance also is infinite.
Arens
I've read a lot about special relativity, and what i don't understand is that speed of lights is the highest speed that a particle can reach.
If we look to this simple experiment, i want to show, maybe you will understand better my thoughts.
We are moving inside a car with a speed of 100 miles/h, and there is someone out of the car in the road standing up, not moving. I am sit in the back of the car, In the moment before we pass the guy standing outside i through a ball in the front car window. Me in inside see the ball moving with 5 miles/h, but the guy outside see the ball moving much faster from his point of view the ball is moving 100 miles/h + 5 miles/h = 105 miles/h.

If we have a particle, moving at speed of light, from a point A of a galaxy, to a point B of the same galaxy, and that galaxy itself is moving with a known speed, in the same direction as our particle, and if we are inside the galaxy we see this particle moving with the speed of light, but if we stand out of this galaxy, as an outside reference point we will see the particle moving faster than light speed.

And now i will go in abstract, but is just my thought.
Universe (not the only one from BB theory) that we know, is INFINITE. If universe is infinite than distance also is infinite. Now if our particle is seen from many infinite point reference points, it travel with infinite speed.
S(speed)=Di(infinite distance)/T(time)

I'd refute you, but I don't have the scientific background to explain fully. So just allow me to say that the speed of light really IS an absolute limit, and the universe will not allow you to pass it. No matter how fast you're going when you shine a light, it will go at the speed of light and no faster.

If I understand your first point correctly, your mistake lies in assuming that classical vector additions apply at relativistic speeds. For high speeds, in order to add one must use a different vector addition formula which you can read up on Wikipedia under the SR section: http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_theory_of_relativity

Your second point seems a bit muddled. The particle itself isn't traveling an infinite distance as seen by a single observer as per his measured time interval so its coordinate velocity won't be infinite.

How have you read a lot about special relativity yet don't understand this most basic tenant of it?

That's the thing about special relativity, particles traveling at near the speed of light don't add up velocities just like you normally add up velocities in your day to day experience.

The prototypical example example you see in textbooks goes something like this: You have a spaceship moving at 1/2 the speed of light, or 0.5c. The spaceship then fires super ridiculously fast missile at 3/4 the speed of light, or 0.75c. What velocity does an observer watching this happen see the missile fly off at?

Your everyday instinct tells you "duh, it goes off at 1.25c, 125% the speed of light" but that's not what special relativity says!

It turns out the velocity the observer at rest sees the missile fly off at is given by

$$v = {{v_{spaceship} + v_{missile}}\over{{1+ {{v_{missile}v_{spaceship}}\over{c^2}}}}}$$

You can show that this is NOT 1.25c. That's the whole point of special relativity. Now, what you hopefully notice is that if the speed of the spaceship and speed of the missile are much much less than the speed of light, then the denominator will become 1 and you get the typical velocity addition you're use to in everyday life.

Ok, I'm giving just a thought of mine, btw everything is relative, nothing is absolute.
if u see our universe from another point of view and it resize inside an electron orbiting in an atom. Tell me why it couldn't be! And i as well said : let's think for a moment that our universe resize inside an electron orbiting in an atom. That atom stays inside a molecule of a football game ball. We know that our particle that is moving inside our universe with the speed light, needs a time T=D/C to go from a point to another point, before our particle reach point B and someone kicks the ball, where our universe is, CAN SOMEONE TELL ME NOW, what speed is our particle moving after the kick, if you look it as a reference point outside the ball??

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Hi, Arens,

Welcome to PF!

Arens said:
Universe (not the only one from BB theory) that we know, is INFINITE.

-Ben

bcrowell said:
Hi, Arens,

Welcome to PF!

-Ben

Thanks for the welcome :)

Arens said:
Ok, I'm giving just a thought of mine, btw everything is relative, nothing is absolute.
Now let we say that, our universe is that big same as an electron and it is inside that electron orbiting around an atom. That atom stand inside the molecules of a football game ball. We know that our particle that is moving inside our universe with the speed light, needs a time T=D/C to go from a point to another point, before our particle reach point B and someone else kick the ball where our universe is, inside its atom , CAN SOMEONE TELL ME NOW, what speed is our particle moving, if you look it as a reference point outside the ball??

What the heck are you talking about?

Pengwuino said:
What the heck are you talking about?

Hmm.. If you could be more polite and read before post, will be great. What we see around is infinite. I wrote that if u see our universe from another point of view and it resize inside an electron orbiting in an atom. Tell me why it couldn't be! And i as well said : let's think for a moment that our universe resize inside an electron orbiting in an atom. That atom stays inside a molecule of a football game ball. We know that our particle that is moving inside our universe with the speed light, needs a time T=D/C to go from a point to another point, before our particle reach point B and someone kicks the ball, where our universe is, CAN SOMEONE TELL ME NOW, what speed is our particle moving after the kick, if you look it as a reference point outside the ball??

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Arens said:
Hmm.. If you could be more polite and read before post, will be great. What i wrote is that if u see our universe from another point of view it would be big as same size or less of an electron orbiting in an atom. What we see around is infinite. Tell me why it couldn't be! And i as well said : let's think for a moment that universe is that big same as an electron and it is inside that electron orbiting around an atom. That atom stand inside the molecules of a football game ball. We know that our particle that is moving inside our universe with the speed light, needs a time T=D/C to go from a point to another point, before our particle reach point B and someone else kick the ball, where our universe is, inside one of the ball atom , CAN SOMEONE TELL ME NOW, what speed is our particle moving, if you look it as a reference point outside the ball??

I read your post about three times and still couldn't figure out exactly what you're saying. Please use proper punctuation and grammar so we have a chance of knowing what you're trying to ask.

What do you mean "why it couldn't be"? Why couldn't what be? What do you mean what we see around is infinite? Beyond that I don't know what you're trying to ask.

Ok. writing again!
if u see our universe from another point of view and it resize inside an electron orbiting in an atom. Tell me why it couldn't be! And i as well said : let's think for a moment that our universe resize inside an electron orbiting in an atom. That atom stays inside a molecule of a football game ball. We know that our particle that is moving inside our universe with the speed light, needs a time T=D/C to go from a point to another point, before our particle reach point B and someone kicks the ball, where our universe is, CAN SOMEONE TELL ME NOW, what speed is our particle moving after the kick, if you look it as a reference point outside the ball??

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Arens, I'm having a hard time understanding your #5. It would be helpful if you could use standard punctuation and grammar. I assume you're not a native English speaker, but you can still use a spellchecker and not write in textspeak ("i" for "I," etc.) Please also make sure you understand the section of the rules https://www.physicsforums.com/showthread.php?t=414380 on overly speculative posts.

Sorry is hard to write perfect english sometime, :P. but i wrote again, think now is in a good grammar, give it a look. :)

Arens said:
Ok. writing again!
if u see our universe from another point of view and it resize inside an electron orbiting in an atom. Tell me why it couldn't be! And i as well said : let's think for a moment that our universe resize inside an electron orbiting in an atom. That atom stays inside a molecule of a football game ball. We know that our particle that is moving inside our universe with the speed light, needs a time T=D/C to go from a point to another point, before our particle reach point B and someone kicks the ball, where our universe is, CAN SOMEONE TELL ME NOW, what speed is our particle moving after the kick, if you look it as a reference point outside the ball??

Why do you want the whole universe inside a football? Why can't you simply consider an electron inside the football? Or light going between atoms inside the football?

If you try to put the universe in a box or football or whatever and try to detach your observer from it, you're losing what it means to measure velocities in any meaningful way.

Pengwuino said:
Why do you want the whole universe inside a football? Why can't you simply consider an electron inside the football? Or light going between atoms inside the football?

If you try to put the universe and try to detach from it, you're losing what it means to measure velocities in any meaningful way.

what i mean is that our universe resize inside an electron orbiting one atom of that ball.

From what i said above, i mean that the highest speed is not the light speed of 299,792,458 m/s, but Speed= infinite

Arens said:
From what i said above, i mean that the highest speed is not the light speed of 299,792,458 m/s, but Speed= infinite

Your question is unphysical. You can't put the universe in a box and do things to it, it makes no sense.

Pengwuino said:
Your question is unphysical. You can't put the universe in a box and do things to it, it makes no sense.

My perception of universe is that it is infinite. This says it all :)

Arens said:
From what i said above, i mean that the highest speed is not the light speed of 299,792,458 m/s, but Speed= infinite

OK, now I think I see what you're getting at.

A couple of suggestions:
-Let's drop the idea that we're fitting the entire universe into a small space. The universe may very well be infinite -- we don't know. (Did you read the link to the FAQ that I posted?) All that's really necessary for your argument is some very large space -- say the solar system -- is compressed down to the size of an atom. It doesn't need to be the whole universe.
-We get a lot of people posting on this site who think they can prove that relativity is wrong, etc. It gets tiresome. You will get more helpful responses if you just say, "here is a paradox, how do you think it can be resolved?" The ALL CAPS creates the impression that you're angry, which doesn't help.

GR does not have any preferred scale, so it's true that you can take any solution to the Einstein field equations and compress it spatially by any factor you like, and it's still a solution to the Einstein field equations. In fact, GR allows you to do any smooth, one-to-one coordinate transformation you like. However: (1) The speed of light doesn't change under such a transformation. (2) The matter that lives inside a spacetime obeys laws of physics that are *not* scale-invariant in this way. For example, if you take a hydrogen atom wavefunction and scale it down by a factor of 1000, it's no longer a solution to the Schrodinger equation. This is ultimately because theories like quantum mechanics contain universal constants like Planck's constant, which set preferred scales that are not present in bare GR.

-Ben

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bcrowell said:
OK, now I think I see what you're getting at.

A couple of suggestions:
-Let's drop the idea that we're fitting the entire universe into a small space. The universe may very well be infinite -- we don't know. (Did you read the link to the FAQ that I posted?) All that's really necessary for your argument is some very large space -- say the solar system -- is compressed down to the size of an atom. It doesn't need to be the whole universe.
-We get a lot of people posting on this site who think they can prove that relativity is wrong, etc. It gets tiresome. You will get more helpful responses if you just say, "here is a paradox, how do you think it can be resolved?" The ALL CAPS creates the impression that you're angry, which doesn't help.

GR does not have any preferred scale, so it's true that you can take any solution to the Einstein field equations and compress it spatially by any factor you like, and it's still a solution to the Einstein field equations. In fact, GR allows you to do any smooth, one-to-one coordinate transformation you like. However: (1) The speed of light doesn't change under such a transformation. (2) The matter that lives inside a spacetime obeys laws of physics that are *not* scale-invariant in this way. For example, if you take a hydrogen atom wavefunction and scale it down by a factor of 1000, it's no longer a solution to the Schrodinger equation.

-Ben

Sorry for caps. I am not proving that relativity is wrong. I am not saying that light speed changes. Speed light is same everywhere! what I am saying is that speed light isn't the highest speed in the all universe.
Arens. :)

Be very careful, you are engaging in speculation. There are no observations from outside of our universe, so how can your ideas be validated. At Physics Forums we do not allow discussion of such speculations.

You would do well to spend some time reading and learning before attempting to find errors in the current state of physics.

## 1. What is the speed of light?

The speed of light is a fundamental constant in physics, denoted by the letter c. In a vacuum, it has a value of approximately 299,792,458 meters per second (m/s). This is the maximum speed at which all forms of matter and information can travel.

## 2. How did scientists discover the speed of light?

The speed of light was first measured by Danish astronomer Ole Rømer in the 17th century. He observed the difference in timing of the eclipses of Jupiter's moons as the Earth moved closer to or further from Jupiter in its orbit. This led to the first estimation of the speed of light at 220,000 km/s.

## 3. What is special relativity?

Special relativity is a theory developed by Albert Einstein in 1905 that explains the relationship between space and time. It states that the laws of physics are the same for all observers in uniform motion and that the speed of light is constant in all inertial frames of reference.

## 4. How does special relativity impact our understanding of the speed of light?

Special relativity revolutionized our understanding of the speed of light by showing that it is the same for all observers, regardless of their relative motion. This means that no matter how fast an observer is traveling, they will always measure the speed of light to be the same value of approximately 299,792,458 m/s.

## 5. Can anything travel faster than the speed of light?

According to the theory of special relativity, nothing can travel faster than the speed of light. As an object approaches the speed of light, its mass increases, making it more and more difficult to accelerate. This makes it impossible for anything with mass to reach or exceed the speed of light.

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