# Thread: Speed of light vs mass limit?

1. Newbie
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Aug 2008
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## Speed of light vs mass limit?

I have checked here and can't seem to find the answer to this question:

My understanding is that as an object approaches the speed of light its mass increases, wouldn't then any object with mass become a black hole as it reached the gravitational limit as it was accelerated?
Is this what may happen in the LHC as protons are accelerated and smashed?

Thanks
Dan

2. Established Member
Join Date
Oct 2007
Posts
1,904
I have checked here and can't seem to find the answer to this question:

My understanding is that as an object approaches the speed of light its mass increases, wouldn't then any object with mass become a black hole as it reached the gravitational limit as it was accelerated?
Is this what may happen in the LHC as protons are accelerated and smashed?

Thanks
Dan
From the relativity faq:

Nick

I have checked here and can't seem to find the answer to this question:

My understanding is that as an object approaches the speed of light its mass increases, wouldn't then any object with mass become a black hole as it reached the gravitational limit as it was accelerated?
Is this what may happen in the LHC as protons are accelerated and smashed?

Thanks
Dan
If you have read Nick Theodorakisī excellent links, especially the second "long answer" link (thank you for this link, Nick), you should be aware of the tricky nature of "relativistic mass". Itīs astonishing that Einstein himself tried to avoid the concept of relativistic mass already in 1948, and still, itīs used in todayīs textbooks.

I explained it to myself this way: Imagine a ball of, say, mass = 1kg. Accelerate it to .8 c (= 80% of the speed of light) relative to your position. Some minutes later you accelerate to .95 c, same direction as the ball. After a while, you will catch up with the ball (wonīt you?) and adjust your speed to the ballīs speed (velocity). Assuming you have all the means necessary to measure the ballīs mass, what mass will you measure? 1 kg!
If you donīt believe it, just try it. Again and again, in a Gedankenexperiment.

You see, this is why I "hate" the concept of relativistic mass, and I fully agree with Philip Gibbsī statement

... relativistic mass is of no use at all ...

4. Newbie
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Thanks for the answers, now I am off to get a handle on relativistic mass.

Dan

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Taking another tack: classical (Newtonian) physics tells us that it requires more energy to accelerate a larger mass. As an object's speed increases, its relativistic mass increases, approaching infinite mass as speed approaches c. Thus, as velocity approaches c, the energy required to go any faster will approach infinity, meaning the entire universe does not have sufficient energy to accelerate a physical mass to the speed of light. The available energy for acceleration may be an effective block to accelerating any mass sufficiently to create a relativistic BH.

6. Originally Posted by Gandalf223
... As an object's speed increases, its relativistic mass increases, approaching infinite mass as speed approaches c. ...
Relativistic mass is a bitterly unhappy "definition" of the expression mo/(1-vē/cē)1/2 which makes many people believe that the mass of an object increases as its speed increases.

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