# Speed of light limit

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#### killium

##### Guest
The more one will try to accelerate an object, the more it will resist acceleration by raising it's total mass. Suppose there is an object somewhere in space that had never have any contact with Earth in the past. This object ALREADY have some vectorial speed relative to earth. Suppose this object has some kind of engine on board and fires it. If this action "adds" some speed to the object relative to Earth, the acceleration should be less than what it should be due to the object having more mass (as seen from Earth). It would imply that NOTHING in the whole universe moves faster than C, RELATIVE to ANY other things in the universe as if everything KNEW about the speed of everything else. How could this be ?

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#### neomaine

##### Guest
Hmmm...

If two objects are moving at .75c and are moving exactly away from each other they are each still moving at .75c. Their relative speed to each other will be 1.5c.

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#### origin

##### Guest
neomaine":2cci9cz7 said:
Hmmm...

If two objects are moving at .75c and are moving exactly away from each other they are each still moving at .75c. Their relative speed to each other will be 1.5c.
Nope that can't happen, that would mean that a light beam sent from one object could not 'catch' the other object. And that would be breaking the law, a physical law, which can't happen.

Good question in OP, I will have to noodle that.

S

#### SpeedFreek

##### Guest
origin":1hgjbck0 said:
neomaine":1hgjbck0 said:
Hmmm...

If two objects are moving at .75c and are moving exactly away from each other they are each still moving at .75c. Their relative speed to each other will be 1.5c.
Nope that can't happen, that would mean that a light beam sent from one object could not 'catch' the other object. And that would be breaking the law, a physical law, which can't happen.

Good question in OP, I will have to noodle that.
Their relative speed would be 1.5c, but only from the frame of reference of a third observer. Each object would calculate the other to be receding at less than c, of course.

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#### origin

##### Guest
SpeedFreek":2hsgpwd3 said:
origin":2hsgpwd3 said:
neomaine":2hsgpwd3 said:
Hmmm...

If two objects are moving at .75c and are moving exactly away from each other they are each still moving at .75c. Their relative speed to each other will be 1.5c.
Nope that can't happen, that would mean that a light beam sent from one object could not 'catch' the other object. And that would be breaking the law, a physical law, which can't happen.

Good question in OP, I will have to noodle that.
Their relative speed would be 1.5c, but only from the frame of reference of a third observer. Each object would calculate the other to be receding at less than c, of course.
Yup, thanks for the clarification SpeedFreak! You da man as always...

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#### Jerromy

##### Guest
The light that was emitted from an object moving at .75c would be no faster or slower than light emitted from a stationary object. If the observer of that light was moving away from the source at .75c it would take 4 times as long for the light to reach them relative to a stationary observer. Galaxies recede from each other at relative velocities greater than the speed of light but eventually the light does make the trip.

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#### killium

##### Guest
SpeedFreek":2xzotthk said:
origin":2xzotthk said:
neomaine":2xzotthk said:
Hmmm...

If two objects are moving at .75c and are moving exactly away from each other they are each still moving at .75c. Their relative speed to each other will be 1.5c.
Nope that can't happen, that would mean that a light beam sent from one object could not 'catch' the other object. And that would be breaking the law, a physical law, which can't happen.

Good question in OP, I will have to noodle that.
Their relative speed would be 1.5c, but only from the frame of reference of a third observer. Each object would calculate the other to be receding at less than c, of course.
So a light beam sent from one object will "catch" the other object ? So SpeedFreek's third observer would see that light beam running at 1.5c ?

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#### SpeedFreek

##### Guest
killium":20dt1a49 said:
So a light beam sent from one object will "catch" the other object ? So SpeedFreek's third observer would see that light beam running at 1.5c ?
Yes, the light from one will reach the other, because neither is moving faster than c. Nobody sees the light beam moving faster than c, as everything is moving at less than c, relative to space, but light moves at c relative to space. The third observer will see each object moving away from their origin point in space at .75c, in opposite directions. That third observer will therefore calculate that the objects are separating at 1.5c, but the observer understands that neither is traveling faster than light. If each object shines a light towards the other, that light will propagate at c. Each object is only moving away from the origin at .75c, so the light from each object will reach the origin point. Then, as each object is only moving at .75c relative to that origin, the light that has now reached the origin will eventually reach the other object, at c!

And due to the time-dilation and length contraction between the objects themselves, each calculates the other is receding at less than c, so there is no surprise from their point of view that the light from one can reach the other.

S

##### Guest
Speed of Light: Besides what has been broadcast in articles lately is there anything in the Universe that could "impede" the speed of light in the Universe?

If light is moving thru the Universe and is being uniformly impeded in its movement....that could explain its magnitude of velocity being 300,000km/s. Where if its movement was not impeded...its "real" velocity could be much higher.

I figure if a light wave's movement thru the Universe is being impeded...that the speed of light could be different than what people measure today....is there any weight to this idea?
Thank you.
SC

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#### ramparts

##### Guest
killium":kar5ug2r said:
The more one will try to accelerate an object, the more it will resist acceleration by raising it's total mass. Suppose there is an object somewhere in space that had never have any contact with Earth in the past. This object ALREADY have some vectorial speed relative to earth. Suppose this object has some kind of engine on board and fires it. If this action "adds" some speed to the object relative to Earth, the acceleration should be less than what it should be due to the object having more mass (as seen from Earth). It would imply that NOTHING in the whole universe moves faster than C, RELATIVE to ANY other things in the universe as if everything KNEW about the speed of everything else. How could this be ?
It looks like this original question hasn't been answered.

I'm a bit puzzled by the first couple of assumptions. There is an object which has had "no contact with Earth" - what do you mean by that? Do you mean it doesn't know anything about the Earth's position, etc.? Because that would imply it's outside of the Earth's light cone (i.e., too far away for even light to reach it), and then it actually doesn't make sense to talk about its velocity relative to Earth.

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