Speed, mass increase & outside observers.

In summary, the concept of mass and motion becomes complicated when considering the perspective of an observer within a spacecraft. If there are no external factors to indicate motion, one could consider themselves stationary. But when accelerating to near light speed, the mass of the craft may appear to increase, causing confusion as to whether it has actually changed or not, as there is no external reference point. However, from the perspective of the observer, there is no change and therefore it cannot be said to have truly increased.
  • #1
Endervhar
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Imagine you are in your spacecraft , and within your observable universe there is no other body. As far as you are aware, you are stationary. If you shine a light inside your craft you will measure its speed as 300,000kps, as you also will if you shine a light outside the craft. Nothing gives you any information about your possible state of motion, so you are quite justified in thinking that you are at rest. Now, if you accelerate your craft so that your instruments tell you that you are traveling at approaching the speed of light, what happens to the mass of your craft? You will be aware of no change, if you were, you would know that you were in motion. If there were an outside observer, she would measure your craft’s mass as approaching infinity as you neared light speed, but there is no external observer, and in your frame of reference nothing has changed. As there is no-one in whose frame of reference your craft’s mass has increased, can it, in fact, be said to have increased?
 
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  • #2
Endervhar said:
Imagine you are in your spacecraft , and within your observable universe there is no other body. As far as you are aware, you are stationary. If you shine a light inside your craft you will measure its speed as 300,000kps, as you also will if you shine a light outside the craft. Nothing gives you any information about your possible state of motion, so you are quite justified in thinking that you are at rest. Now, if you accelerate your craft so that your instruments tell you that you are traveling at approaching the speed of light, what happens to the mass of your craft?
Your speed relative to what? Assuming that your craft has external sensors so that for its "observable universe" there are other bodies then it can give your speed relative to one of those bodies. But, of course, it would really tell you that the other bodies are going faster relative to you. From the point of view of the craft, you are still stationary.

You will be aware of no change, if you were, you would know that you were in motion. If there were an outside observer, she would measure your craft’s mass as approaching infinity as you neared light speed, but there is no external observer, and in your frame of reference nothing has changed. As there is no-one in whose frame of reference your craft’s mass has increased, can it, in fact, be said to have increased?
There is absolutely no reason to say it has increased or, in fact, that your speed has changed. Why is that a problem?
 
  • #3
Even with no other observable body, would you not be aware that you were in motion while you were accelerating?
 

1. How does speed affect mass increase?

According to Einstein's theory of relativity, as an object approaches the speed of light, its mass increases. This is because the object's energy also increases, and mass and energy are equivalent according to the famous equation E=mc^2.

2. Can an object actually reach the speed of light?

No, according to the theory of relativity, an object with mass would require infinite energy to reach the speed of light. Therefore, it is impossible for an object with mass to travel at the speed of light.

3. How does mass increase affect an object's movement?

As an object's mass increases, it becomes more difficult to accelerate it further. This is because more energy is required to increase the object's speed due to its increased mass.

4. How does an outside observer perceive an object's mass increase?

From the perspective of an outside observer, an object traveling at high speeds would appear to have a greater mass than it actually does. This is due to the effects of time dilation and length contraction, which are also predicted by the theory of relativity.

5. Does mass increase only occur at high speeds?

No, mass increase, also known as relativistic mass, occurs at any speed. However, the effects are only significant at speeds approaching the speed of light. At lower speeds, the change in mass is negligible and can be ignored in most practical situations.

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