Can you see an object approaching c grow?

[Baby Astronaut]

When an object travels at nearly the speed of light, it gains mass. My question is, how does its mass gain look to an observer?

 

Let's say the object is a spacecraft leaving the galaxy, and you're here on Earth. If you had observed the people inside the spacecraft (from its departure until it eventually attained the near-light speed), would you have witnessed each person growing in size?

 

Would the travellers have noticed their own growth while it happened?

 

And if they continued on the way to gaining near-infinite mass, does that mean you'd eventually see their physical bodies and spacecraft expanding into our solar system (from their other end which is still in a distant galaxy), due to the cosmic mass gain?

 

Or does the mass gain cause an increase of density rather than size? Or does it cause both? Or would they transform into a star first and then a black hole after a certain point of mass gain?

[Kyrisch]

The mass only appears to increase due to energy-mass equivalence. There is no growth in size.

[Baby Astronaut]

Does that mean it's only a virtual increase of mass, like saying in order to go faster, the object would need that much more energy as if it really had the extra mass?

[Klaynos]

This is why I don't like having invariant mass...

 

http://en.wikipedia.org/wiki/Mass_in_special_relativity#Controversy

[Baby Astronaut]

Thanks for the link Klaynos.

 

So, there's a dispute of whether the theory works for rest mass or relativistic mass?

 

Here's what I understood: rest mass is easier to determine because, unless I'm mistaken, the energy of relativistic mass adds the energy of the whole system it's in. But we exist in a subsystem of a subsystem of a subsystem, etc.

 

If that's correct, don't we have part of the speed needed for reaching light speed already supplied to us by the speed of our cosmic surroundings? Which, if objects truly weigh more the faster they move, we'd probably be able to move easier if our surrounding cosms would just slow it down a bit

 

OK, back to earth. Is it really a virtual mass gain, and if so, is it by density? Or does the mass remain with both its original density and size, and only increases its weight?

[swansont]

The object, in its own frame, is at rest. It sees nothing different.

 

The question "Is it really a virtual mass gain, and if so, is it by density?" requires that you define which mass you are using, and how you are doing your measurements. Rest mass and relativistic mass are not interchangeable, and not really compatible in the same discussion. (and if you go far enough in the calculations, relativistic mass breaks the symmetry of Minkowski spacetime)

[Baby Astronaut]

The question "Is it really a virtual mass gain, and if so, is it by density?" requires that you define which mass you are using, and how you are doing your measurements.

Not really sure what you mean. If you can elaborate please (but keep it in layman terms)?

[Baby Astronaut]

Not really sure what you mean. If you can elaborate please (but keep it in layman terms)?

*bump*

[swansont]

There is rest mass, and there is relativistic mass. They are not the same, nor are they interchangeable. (In fact, the physics you use changes somewhat if you use relativistic mass — it's a term of convenience)

 

So, which one you are using affects the answer. Using rest mass, there is no mass change of an object when it's moving.

[Baby Astronaut]

Is it really a virtual mass gain, and if so, is it by density? Or does the mass remain with both its original density and size, and only increases its weight?

 

There is rest mass, and there is relativistic mass. They are not the same, nor are they interchangeable. (In fact, the physics you use changes somewhat if you use relativistic mass — it's a term of convenience)

 

So, which one you are using affects the answer.

What if my question is applied to relativistic mass?

[Baby Astronaut]

*bump*

 

What if my question is applied to relativistic mass?

[swansont]

If you use relativistic mass, the mass increases because you've defined mass to be E/c^2, and you've increased the energy.

[Baby Astronaut]

But is it a virtual mass gain? In other words, is it a mass gain only in the sense that it gains weight (and/or it's needed to make related physics calculations valid), but visually you wouldn't see the gain?

[Gilded]

But is it a virtual mass gain? In other words, is it a mass gain only in the sense that it gains weight (and/or it's needed to make related physics calculations valid), but visually you wouldn't see the gain?

 

How can you "visually see" how much mass something has? Anyway, it's a relative gain and in this case happens as noted by swansont, and can be observed. I don't know what your definition of virtual is but I'd say there's a relativistic truckload of evidence to support the fact that relativity is in fact very real.

[Baby Astronaut]

How can you "visually see" how much mass something has?

The same way you can determine that a mountain has greater mass than an apple.

 

Anyway, it's a relative gain and in this case happens as noted by swansont, and can be observed. I don't know what your definition of virtual is...

Refer to the parts in bold from my opening question, quoted below.

 

When an object travels at nearly the speed of light, it gains mass. My question is, how does its mass gain look to an observer?

 

Let's say the object is a spacecraft leaving the galaxy, and you're here on Earth. If you had observed the people inside the spacecraft (from its departure until it eventually attained the near-light speed), would you have witnessed each person growing in size?

 

Would the travellers have noticed their own growth while it happened?

 

And if they continued on the way to gaining near-infinite mass, does that mean you'd eventually see their physical bodies and spacecraft expanding into our solar system (from their other end which is still in a distant galaxy), due to the cosmic mass gain?

 

Or does the mass gain cause an increase of density rather than size? Or does it cause both? Or would they transform into a star first and then a black hole after a certain point of mass gain?

What I mean by virtual, is not a real mass gain per se, such as how we understand objects with greater and greater mass have more of a gravity pull, weight and size, eventually becoming a star and then a black hole.

 

So by virtual, I mean an object is treated as having the extra mass, but it doesn't have the associated gravity pull, size, or collapsing into nuclear fusion problems. Maybe it does have the weight though.

[Moontanman]

The same way you can determine that a mountain has greater mass than an apple.

 

Size and mass are not interchangeable. It is possible for a object the size of an apple to be more massive than the mountain.

 

Refer to the parts in bold from my opening question, quoted below.

 

 

What I mean by virtual, is not a real mass gain per se, such as how we understand objects with greater and greater mass have more of a gravity pull, weight and size, eventually becoming a star and then a black hole.

 

It's my understanding that the mass increase is quite real.

 

So by virtual, I mean an object is treated as having the extra mass, but it doesn't have the associated gravity pull, size, or collapsing into nuclear fusion problems. Maybe it does have the weight though.

 

The object does have the extra mass, it come from the energy you put into accelerating the object to near light speed. The only visual effect would be the object or space craft being shortened along the axis of acceleration.

[swansont]

What I mean by virtual, is not a real mass gain per se, such as how we understand objects with greater and greater mass have more of a gravity pull, weight and size, eventually becoming a star and then a black hole.

 

So by virtual, I mean an object is treated as having the extra mass, but it doesn't have the associated gravity pull, size, or collapsing into nuclear fusion problems. Maybe it does have the weight though.

 

You've chosen "relativistic mass" to be the mass under discussion, but have now asked other questions that contradict that use. Such is the problem of equivocation (intentional or not)

 

The relativistic mass is not the term that goes into these equations — a star does not become a black hole because it is moving relative to you and has a larger relativistic mass.

 

This is one reason why rest mass is the more useful term. It's not frame-dependent, and avoids some of this confusion.

[Baby Astronaut]

You've chosen "relativistic mass" to be the mass under discussion, but have now asked other questions that contradict that use. Such is the problem of equivocation (intentional or not)

 

The relativistic mass is not the term that goes into these equations — a star does not become a black hole because it is moving relative to you and has a larger relativistic mass.

 

This is one reason why rest mass is the more useful term. It's not frame-dependent, and avoids some of this confusion.

So what you are saying is that relativistic mass, i.e. it's total energy including momentum, will not have the same properties as its equivalent in rest mass?

 

For example, say an object (A) at "rest" has x units of mass, which is enough to trigger star formation due to its mass quantity alone.

 

Then let's say an object (B) with 10 times less the units of mass were accelerated up to the point that it would now have x units of mass due to its rest mass + its velocity.

 

Conclusion: object B won't collapse into a star because of its mass, even though its units of mass are identical to that of object A. Is that correct?

[Gilded]

Conclusion: object B won't collapse into a star because of its mass, even though its units of mass are identical to that of object A. Is that correct?

 

Yes. As I've understood it an observer will measure the (relativistic) masses as being identical. But for something to collapse due to gravity it would obviously need to have enough mass in its own frame of reference. This is why I haven't been crushed by my own gravity just because high-energy cosmic rays might think I should've.

[Baby Astronaut]

Yes. As I've understood it an observer will measure the (relativistic) masses as being identical. But for something to collapse due to gravity it would obviously need to have enough mass in its own frame of reference.

The frame of reference bit makes it all clear.

 

Also, it shows what I mean by virtual. Because an object will have a minimum amount of mass in any frame of reference, that minimum amount is basically its true mass. Anything more than its rest mass would be virtual, because the object itself can't measure those increases within its own frame of reference.

 

At least I don't believe it can.

[Baby Astronaut]

A couple of things still nagging at me.

 

1. If a spaceship were cruising at near light speed, it would take a vast amount of energy to make it go faster. So logically, you'd need vast amounts of energy to accelerate just the people within the spacecraft as well. Yet I can't imagine them needing a vast reservoir of energy to run from the back of the ship towards its front, which in essence accelerates them.

 

Or better yet, let's say there's a planetary system cruising at near light speed for some unknown reason. If one of its planets were inhabited, its people shouldn't have trouble racing cars or launching a ship in front of the planet, towards the same direction it's cruising in (their star is also cruising along with its planets, so life is about the same as here on Earth).

 

Now, if they went by spaceship and were calculating how much energy they'd need to reach light speed, they'd arrive at a conclusion that the energy needed to get there would increase every step of the way. But since they're already going 99.999% of light speed, they would be going much faster than any Earth ship can. Ironically, that'd be the case even if they took off in the opposite direction. But relatively, they'd be going as fast as us, at least in their own frame of reference.

 

My point is, all that energy required to reach light speed, 99.999% of it has been given to them as a shortcut, and with that in mind, can they achieve light speed by eventually developing superior technology?

 

Let's say we on Earth in a few hundred years develop a ship that goes 99.999% the speed of light. Now, let's say that other planet develops an identical ship, but they're entire planet is already going that speed, so it'd be 99.999% + 99.999% meaning they'd get a lot closer than us. But can they pass the speed of light?

 

2. The new particle accelarator has particles cruising at near light speed. If their mass increases substantially from going that fast, shouldn't they weigh more than our planet?

 

If not, how much do they weigh (in anyone's opinion/calculation)?

[swansont]

A couple of things still nagging at me.

 

1. If a spaceship were cruising at near light speed, it would take a vast amount of energy to make it go faster. So logically, you'd need vast amounts of energy to accelerate just the people within the spacecraft as well. Yet I can't imagine them needing a vast reservoir of energy to run from the back of the ship towards its front, which in essence accelerates them.

 

You're mixing reference frames. Energy isn't an invariant when you go from one frame to another. In the frame of the rocket, someone at rest has no kinetic energy, and someone moving within has only a small amount.

 

 

Or better yet, let's say there's a planetary system cruising at near light speed for some unknown reason. If one of its planets were inhabited, its people shouldn't have trouble racing cars or launching a ship in front of the planet, towards the same direction it's cruising in (their star is also cruising along with its planets, so life is about the same as here on Earth).

 

Now, if they went by spaceship and were calculating how much energy they'd need to reach light speed, they'd arrive at a conclusion that the energy needed to get there would increase every step of the way. But since they're already going 99.999% of light speed, they would be going much faster than any Earth ship can. Ironically, that'd be the case even if they took off in the opposite direction. But relatively, they'd be going as fast as us, at least in their own frame of reference.

 

My point is, all that energy required to reach light speed, 99.999% of it has been given to them as a shortcut, and with that in mind, can they achieve light speed by eventually developing superior technology?

 

Let's say we on Earth in a few hundred years develop a ship that goes 99.999% the speed of light. Now, let's say that other planet develops an identical ship, but they're entire planet is already going that speed, so it'd be 99.999% + 99.999% meaning they'd get a lot closer than us. But can they pass the speed of light?

 

 

Speed (or velocity) is always measure with respect to something — there is no absolute frame of reference. You can't say "they're already going 99.999% of light speed" without that reference.

 

2. The new particle accelarator has particles cruising at near light speed. If their mass increases substantially from going that fast, shouldn't they weigh more than our planet?

 

If not, how much do they weigh (in anyone's opinion/calculation)?

 

Their (rest) mass doesn't change. The notion that it does comes from sloppy mixing of definitions.

[Baby Astronaut]

You're mixing reference frames.

Which reference frames? And how?

 

Energy isn't an invariant when you go from one frame to another. In the frame of the rocket, someone at rest has no kinetic energy, and someone moving within has only a small amount.

Are you saying that for us to move the super fast craft, but doing so from our own frame, we'd need the tremendous energy, but, for the people in their own frame to move that very same craft, they need only the typical amount?

 

Meaning, someone never gets a head-start towards going light-speed by starting off in a faster frame than us?

 

Speed (or velocity) is always measure with respect to something — there is no absolute frame of reference. You can't say "they're already going 99.999% of light speed" without that reference.

But they do when explaining the Large Hadron Collider.

 

"Capable of sending a single proton through the 27KM loop at 99.99% the speed of light, or within 90 milliseconds."

 

Their (rest) mass doesn't change. The notion that it does comes from sloppy mixing of definitions.

Which definitions?

[swansont]

Which reference frames? And how?

 

 

Are you saying that for us to move the super fast craft, but doing so from our own frame, we'd need the tremendous energy, but, for the people in their own frame to move that very same craft, they need only the typical amount?

 

The reference frame of the rocket moving fast relative to you is a different frame than the rocket itself. You can't compare values of energy between those frames.

 

Meaning, someone never gets a head-start towards going light-speed by starting off in a faster frame than us?

 

No, that's not what I said. But to do the comparison you have to remain in the same frame of reference.

 

But they do when explaining the Large Hadron Collider.

 

"Capable of sending a single proton through the 27KM loop at 99.99% the speed of light, or within 90 milliseconds."

 

That's relative to someone standing on the earth. Relative to another proton in the ring, they aren't.

 

Which definitions?

 

Rest mass and relativistic mass. They are not interchangeable. If we limit ourselves to using rest mass, then it is incorrect to say that the mass of a moving body increases.

[Baby Astronaut]

I'm simply not understanding what you're saying.

 

In particular, the quoted parts below. (remember, when using references to other things, I don't have the background you do)

 

The reference frame of the rocket moving fast relative to you is a different frame than the rocket itself. You can't compare values of energy between those frames.

 

No, that's not what I said. But to do the comparison you have to remain in the same frame of reference.

What comparison?

 

Relative to another proton in the ring, they aren't.

?

 

Rest mass and relativistic mass. They are not interchangeable. If we limit ourselves to using rest mass, then it is incorrect to say that the mass of a moving body increases.

When can I use it, and when shouldn't I? Please be clear. (no offense )