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Author Topic:   Misconceptions of E=MC^2
Percy
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Posts: 19408
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 4 of 243 (451966)
01-29-2008 10:50 AM
Reply to: Message 1 by pelican
01-29-2008 10:20 AM


Hi Heinrik,

Chiroptera gave the right answer, but I want to offer a little more clarification.

Chiroptera put the word "proven" between quotes, and he did so because when scientists talking about science use the word "proven" they do not mean it in the same sense as laypeople. Laypeople tend to think of the word "proven" as meaning 100% certainty, but all "proven" means within science is that the idea is supported by sufficient evidence that it has formed a consensus of acceptance within relevant scientific circles. The acceptance is granted provisionally and only until such time as new evidence or improved insight indicates a change is required.

So when a scientist says that E=mc2 has been proven, all he means is that the accuracy of the equation is supported by a great deal of empirical evidence.

--Percy


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Replies to this message:
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Percy
Member
Posts: 19408
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 7 of 243 (451983)
01-29-2008 11:22 AM
Reply to: Message 5 by Chiroptera
01-29-2008 10:52 AM


Chiroptera writes:

And one has to ask, what in the real world is ever known with 100% certainty? One can state that something is not proven unless it is 100% certain, but then the word "proof" has no practical meaning in the real world.

I grant this semantic issue, but I think creationists tend to think of "proven" in a more absolute sense and believe it implies that no other conclusion is possible, the way we think of mathematical and logical derivations. Presenting the issue of tentativity alongside use of the word "proof" is also difficult, often seeming to be a contradiction. Plus creationists think the existence of the Christian God is 100% certain, proven beyond any doubt by the literal truth of the Bible in terms of history and prophecy.

So that's why I take the approach I do, but I'm open to more effective approaches.

--Percy


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Percy
Member
Posts: 19408
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 58 of 243 (452262)
01-29-2008 9:39 PM
Reply to: Message 56 by pelican
01-29-2008 9:11 PM


Re: E=MC2 experiments
Hi Heinrik,

c is a universal constant that can be directly measured because it is equal to the speed of light in a vacuum. The c2 in the equation is just a conversion factor between mass and energy and has nothing to do with how fast the mass is traveling. Using units of meters/second for c, the equation could be rewritten like this:

E = 8.98755179 × 1016 × (meters2/seconds2) × m

So if you converted, say, 5 kilograms of mass to energy, the amount of energy released would be:

E = 8.98755179 × 1016 × (meters2/seconds2) × 5 kg
= 4.49377589 × 1017 kilogram × (meters2/seconds2)
= 4.49377589 × 1017 joules

Does that help?

--Percy


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Percy
Member
Posts: 19408
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 99 of 243 (452380)
01-30-2008 8:30 AM
Reply to: Message 69 by pelican
01-30-2008 12:21 AM


Re: E=MC2 experiments
Heinrik writes:

As it stands e = mc2 i.e the theory of producing matter from energy using the square of the speed of light has never been proved, only the reverse.

The equivalence has been experimentally verified in both directions. The conversion of energy to mass is much more difficult because such huge amounts of energy are necessary to create very little mass.

--Percy


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Percy
Member
Posts: 19408
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 124 of 243 (452811)
01-31-2008 11:16 AM
Reply to: Message 122 by Kapyong
01-31-2008 6:49 AM


Re: E=MC2 experiments
Iasion writes:

Haven't you noticed yet that you keep writing the formula wrong?
e=mc2 is wrong.
The correct formula is e=mc^2.

In the interests of completeness, the formula can be expressed typographically in three ways that I know of:

  • E = mc2
  • E = mc^2
  • E = mc**2

As you noted, E = mc2 is incorrect since it says that energy equals mass times the speed of light times 2, but most people have gotten in the habit of ignoring the mistake because they know what is meant and realize that the mistake is due to what happens when you cut-n-paste "E = mc2", since the fact that the 2 is a superscript doesn't copy.

I'm sure you know all this, this is just for the benefit of Heinrik.

--Percy


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Percy
Member
Posts: 19408
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 160 of 243 (453453)
02-02-2008 9:04 AM
Reply to: Message 149 by molbiogirl
02-01-2008 7:30 PM


Re: mass * the speed of light squared = energy ?
Relativity always turns out to be more complicated than I think, but I believe it would be correct to say that E=mc2 is for a mass at rest with respect to the observer. If the mass were moving at velocity v then the non-relativistic version of the equation might become:

E = mc2 + mv2/2

But mass actually increases with relative velocity, so for a mass in motion I'm guessing that the equation might really be:

E = mc2 + mv2/(2 * (1-v2/c2)1/2)

But I'm just guessing. Modulous's answer in Message 151 may be the correct one, and his equation simplifies to:

E = mc2 / (1-v2/c2)1/2

Anyone know which is correct and why? I'm trying to see how Modulous's answer reduces to mv2/2 (the Newtonian answer) for non-relativistic velocities after subtracting out an mc2, but I can't figure it out.

--Percy


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Replies to this message:
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Percy
Member
Posts: 19408
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.7


Message 165 of 243 (453480)
02-02-2008 10:26 AM
Reply to: Message 164 by cavediver
02-02-2008 9:52 AM


Re: mass * the speed of light squared = energy ?
Thank you. I looked at the Wikipedia article on the Taylor Series and it was a bit beyond me. Is this something that can be explained more simply?

--Percy

Edited by Percy, : Grammar.


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