Why you can't travel faster than the speed of light

[chemtom24]

Why would it be written like that? Surely:

E^2=mc^4+pc^2

Would make more sense?

mathematically you are correct (mc^2)^2 = mc^4, but since m = 0 in this case it doesnt matter.

[chemtom24]

m^2 c^4 sorry

[Big Jim Slade]

Why do electrons have mass?

Eh? Did I say/imply that?

[chemtom24]

jim i wondered why that comment was made too. they do have mass though, they are a fundamental particle (and/or wave for you pedantic lot! )

[Big Jim Slade]

Albert was certainly a smart fellow, but I can't get past the fact that it is only the THEORY of relativity.

Not this one again, surely? There's a big difference between the day to day usage (as in "I have a theory as to why every third Big Mac I buy has an extra gherkin in it", they way you are using the word), and a scientific theory, which is a set of postulates/rules that can be tested by experiment and observation. A scientific theory also allows you to make predications about future behaviour, which again can be tested/observed.

I've not been on SGL that long, but I think you'll find "It's only a theory" goes down like a lead balloon around here.

[Big Jim Slade]

jim i wondered why that comment was made too. they do have mass though, they are a fundamental particle (and/or wave for you pedantic lot! )

Hehe. But what's 1/1836 of the mass of a proton between friends?

[Superewza]

that'd be E^2 = m^2c^4 + p^2c^2

It is sometimes written like that, but i find it neater to write it with the brackets because it allows you to easily think in terms of components, by analogy to Pythagoras:

a^2 = b^2 + c^2

you've got your rest mass term and your momentum term on the right, which you can think of as the vertical and horizontal sides of the triangle

then the energy term on the left is the hypotenuse - it feels more intuitive to me to think of it like that

Ah, i get you. A while since i covered BODMAS.

Eh? Did I say/imply that?

No, but as far as i'm aware it's practically impossible to answer, thought it might have sparked some sort of interesting discussion or parallel with the style of question being asked in the OP... i don't know, just shut up, K?

[chemtom24]

i dont doubt that you are right superewza, however i do wonder then why i have a data book from my chem department that states the mass of an electron is (9.109534 x 10^-31 Kg).

so i must ask why it is thoguht impossible to measure? firstly because i cant think of any reason why it would be, although admittedly it is a very small number, and secondly because i have a value for its mass quoted to 6dp!!

6dp is a mighty fine guess by anyones standards!

[Big Jim Slade]

No, but as far as i'm aware it's practically impossible to answer, thought it might have sparked some sort of interesting discussion or parallel with the style of question being asked in the OP... i don't know, just shut up, K?

Hey, when it comes to this stuff I'm just running on mis-remembered A level physics, my copy of "The New Quantum Universe" and Wikipedia - gimmie a break.

[toml42]

i dont doubt that you are right superewza, however i do wonder then why i have a data book from my chem department that states the mass of an electron is (9.109534 x 10^-31 Kg).

so i must ask why it is thoguht impossible to measure? firstly because i cant think of any reason why it would be, although admittedly it is a very small number, and secondly because i have a value for its mass quoted to 6dp!!

6dp is a mighty fine guess by anyones standards!

I think he asked why it has mass, which is a whole other kettle of fish!

We do have very accurate measurements of electron mass, i actually managed to do it myself up to about 3 dp in 1st year lab at university.

[chemtom24]

I think he asked why it has mass, which is a whole other kettle of fish!

We do have very accurate measurements of electron mass, i actually managed to do it myself up to about 3 dp in 1st year lab at university.

ah. i shouldve read it properly, i do apologise

tom

[chemtom24]

so on that question, cant it be extrapolated to all the particles, and then we can ask why the hell does anythign have mass? what is mass?

this is where my naive physics knowledge breaks down

[toml42]

so on that question, cant it be extrapolated to all the particles, and then we can ask why the hell does anythign have mass? what is mass?

this is where my naive physics knowledge breaks down

Well, that's not bad going on your part, considering that's the point where the collective knowledge of the human race breaks down!

This is actually one of the things the LHC is trying to discover - the Higgs boson (the 'God' particle): you may have heard of it.

If the standard models of particle physics are correct - and they have a pretty good track record so far - then the Higgs boson imbues every particle with mass. We should all be sitting in a Higgs field that gives us our mass.

of course - this might be wrong.

[Macavity]

One could be forgiven for wondering which ideas are current, but:

Lepton - Wikipedia, the free encyclopedia

seems solid (no pun intended) enough.

Aside: Fantastically ROUND... as well!

http://www.guardian.co.uk/science/2011/may/25/electrons-round-cosmos

[rabbithutch]

@rabbithutch: I think you've gone down a blind alley there. You're trying to apply an equation that deals with the relationship between mass and energy, to something that has no mass (a photon). E=mc2 by definition can only be applied to things with mass (I think; IMNAPhysicist etc.)

I confess to being neither a physicist nor a mathematician - nor much of a logician. I was simply trying to point out my ignorance of the equation.

If . . .

E = energy (as an abstract concept? or as a physical quantity?)

L = light (a term I introduce under the precept that light is energy)

m = mass (

then, if . . .

Light = Energy is true, then the speed of light (c^2), it seems to me, is the velocity of energy and the equation as I (mis)understand it represents that Energy is equal to the velocity of itself (c^2) multiplied by mass. Perhaps I'm too literal with my attempt to equate things; and perhaps c^2 refers to some specific energy, not energy as an abstract concept.

As I've said, I can't wrap my brain around this but that is probably because I am too ignorant of too many things to even consider the subject matter.

[chemtom24]

photons have no mass so e=mc^2 has no meaning. photons do have energy tho, and the relationship is given by E=hf, which has been explained above. another relationship is wavelength=h/p , where p=mv (mass x velocity)

i think to say that light is energy may be looking at it backwards, similar analogy to the speed limit of the universe and the speed of light where the speed of light is not determined by light itself but by the universes maximum speed, which is a constant.

you also need a true definition for energy, ie, what is it? im no physicist so i have no idea, but my guess is that it isnt understood yet.

what is understood is that energy, whatever that is, is conserved. when an eletron and a positron annihilate each other, their total mass ( and therefore energy) is converted into a gamma ray. light in the general sense, ie visible light, is only a very small part of the electromagnetic spectrum, and is relatively low in energy.

it therefore follows that light can have energy. as i understand it this energy is stored in the form of a wavelength.

since a photon of light is massless, it seems that it should follow that a photon = wavelength = energy. However I suspect, again, that this is the wrong way to look at it. We can say that a photon carries, or has energy, in the form of a wavelength. but to equate the two 'by-proxy' seems like a jump that shouldnt be made.

I however have no actual physical education, so I may well be wrong, and i do hope someone can correct me in any errors i have made!

[chemtom24]

@rabbithutch ... the term 'c' means the speed of light, which is ~ 3 x 10^8 metres per second. you may often see it written as 3x10^8 ms^-1 . a value to the power of -1 simply means 'per' that unit, eg s^-1 = per second. more mathematically correct it means the number 1 divided by that value. , eg 3^-1 = 1/3

c^2 is the speed of light squared, which if my dodgy maths is ok, is ~ 9x10^16 ms^-1

again i may be fantastically wrong with this so i do hope someone can and will pick me up on it.

[ronin]

Does the total mass of the books you own affect how fast you read?

No, you will find that the books get more massive as you read them slowly.

The idea that this is only a theory isn't true any longer. It was a theory when first thrown out to the world but in the intervening years we have accumulated so much proof of this that it is no longer a theory, just an accepted state of physics.

Dark matter is called dark because we know/knew nothing about it. When we eventually learn about it then it will no longer be "dark" just another, slightly weird, form of matter. But not dark.

X-rays were/are called X becxaue they did not know what they were, X = Unknown. They are now very well known, measured, detected and created but still called X. Taught at GCSE level physics so hardly unknown.

People put the word "theory" in front when postulating their ideas. Somehow it often gets stuck there. Newtion had/has one on Gravity.

[mijijim]

Hi Iw24,

Read the book Tau Zero by Poul Anderson it is a good read on that subject.

Pm me your address and I will send you my copy.

mijijim.

[TFC]

Not this one again, surely? There's a big difference between the day to day usage (as in "I have a theory as to why every third Big Mac I buy has an extra gherkin in it", they way you are using the word), and a scientific theory, which is a set of postulates/rules that can be tested by experiment and observation. A scientific theory also allows you to make predications about future behaviour, which again can be tested/observed.

I've not been on SGL that long, but I think you'll find "It's only a theory" goes down like a lead balloon around here.

I wasn't refering to the Big Mac theory, but the scientific variety.

So far, all the tests, experiments and observations have failed to disprove that travel faster than the speed of light is not possible - that doesn't make it a fact however.

The big bang thoery hasn't yet been disproved, but I get the impression that it is falling out of favour as a sensible explanation for how everything started.

[Syzygy2011]

And theorist's in the 40's said that the sound barrier couldn't be broken????

[noakesy]

if i was taller could have stopped that going over my head,, how heavy / interesting was that... ta

[scogyrd]

This thread has got me thinking, what is the difference between a scientific theory and a scientific law? For example why is the second law of thermodynamics a law but the theory of special relativity a theory? What does it take for a theory to become a law?

[todd8137]

but if you could , and the machine you was traveling in had head lights,how fast would the light of the head lights be traveling at ?

[Earl]

Well, that's not bad going on your part, considering that's the point where the collective knowledge of the human race breaks down!

This is actually one of the things the LHC is trying to discover - the Higgs boson (the 'God' particle): you may have heard of it.

If the standard models of particle physics are correct - and they have a pretty good track record so far - then the Higgs boson imbues every particle with mass. We should all be sitting in a Higgs field that gives us our mass.

of course - this might be wrong.

I was watching Through the worm hole last night which was talking about this.

Could the Higgs field be Dark Energy?