Speed of Light

Mike Hewson
Mike Hewson
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RE: if mass increase with

Message 59019 in response to message 59018

Quote:
if mass increase with the speed increase then why ordinary objects no matter how small mass they have - why dont they become black-holes when accelerated to high enough speed ?


I think they are proposed to do that if sufficient mass/energy was applied. You need enough of it condensed to the small enough volume/radius to make the 'escape' velocity greater than light speed. That and whether or not classical GR is adequate at that level anyway, not having QM involved. :-)

There's alot of interpretative issues and modelling that is applied when we move away from human scales of length, energy, mass etc.

Indeed is it the Brookhaven Lab that is going to look into this, with their heavy ion facilities ?

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

debugas
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RE: RE: if mass increase

Message 59020 in response to message 59019

Quote:
Quote:
if mass increase with the speed increase then why ordinary objects no matter how small mass they have - why dont they become black-holes when accelerated to high enough speed ?

I think they are proposed to do that if sufficient mass/energy was applied.

No they are not.
Just think about it :) - for two different observers both in inertial frames one would think the object is a black-hole and the other would think it is not a black-hole ?

The thing is gravitational-mass does not change so the objects do not become black holes at all. It is only inertial mass that increases with speed increase.

You wrote it yourself:

Quote:

It's probably easier to state that the inertia of massive bodies increases with speed. This implies that it requires more force/energy/momentum input to induce a given velocity increase, as you go faster. You could then 'blame' the mass changing for that greater 'sluggishness'.

i'd only reverse the last part - the 'sluggishness' (which is absent in classical view with low velocities) then can be called extra mass in order to interprete high-speeds theory in terms of classic (low-speeds) one.
However this interpretation is not completely correct and if applied as 100% accurate it is misleading and it leads to paradoxes

debugas
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I'd like to continue and

Message 59021 in response to message 59020

I'd like to continue and point out one more notion which is well defined in classic (low speeds theories) and is artificial artefact in high speeds theories.

The notion in question is Force.
At high speeds (comparable to the speed of light) the Force is dependend on object's speed vector.
For some reason we still claim the Forces are real - we are so used to them in classical (low speeds) theories that we attempt to think in terms of forces at high speeds even though we clearly see the notion is ridiculous.
There are no forces in nature!
It just happens the laws of nature are such that in low-speed limit ( when light speed is infinite) we can interprete them as forces.

Mike Hewson
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RE: No they are not..... it

Message 59022 in response to message 59020

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No they are not..... it leads to paradoxes


Experimentally it's precisely the point of the exercise to see whether gravitational mass == inertial mass, and whether energy and mass are always truly equivalent. So Brookhaven is going to throw things together and see if they can detect the signature radiation of 'mini-black holes'. I think the implication is to seek to see if the near space ( which will be a tiny radius ) can be so stuffed full of mass/energy that photons will at least temporarily trap. This also assumes ( there is a long list of assumptions in this research ) Hawking type radiation for that energy to be released back out for our measurement.

I wasn't talking of an a-priori selection of theory variant, but measurement to compare proposed models of gravity in the small. While a 'distant' lab observer in an inertial frame may interpret dynamic changes as reflecting mass increase, the close-in space may viewed as non-inertial with respect to that. In any case viewing an accelerated particle from separate inertial frames still involves the history of the acceleration of that particle with respect to either. In that sense acceleration is an absolute that can't be 'framed away' except by going to a full GR treament, if done then those separate inertial observers will still both see a black hole ( but may disagree upon it's exact mass/energy content ). As General Relativity is a generalisation of Special Relativity one can begin by approximating with SR then adjusting with GR - experiment will decide whether that was a good enough exercise.

As for 'forces': well Einstein posited geodesics as the lines within an accelerated frame ( that seem to curve from the view of a distant inertial frame ) that removed gravity as a force description and inserted spacetime as warped. Alas other force types haven't geometrised in that regard ( yet ... see String Theory ).

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

debugas
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RE: accelerated

Message 59023 in response to message 59022

Quote:
accelerated particle


sorry i was not talking about accelerated particle.
I was talking about a particle moving with constant speed close to speed of light (retalive to non-moving observer)

Erik
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"Scientists have apparently

"Scientists have apparently broken the universe's speed limit. For generations, physicists believed there is nothing faster than light moving through a vacuum - a speed of 186,000 miles per second. But in an experiment in Princeton, N.J., physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering. The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum."

Link

gravitysmith
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RE: "Scientists have

Message 59025 in response to message 59024

Quote:
"Scientists have apparently broken the universe's speed limit.

True, but it can't be used to violate causality (learning of something before it happens). This one is tricky because it calls into question what defines the location of a pulse. Is it the peak? Is it the beginning, and if so, what defines where it begins?

I wrote a bit more about this in a much earlier post about the "superluminal" light.

smith

Mike Hewson
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Well, it's apples and oranges

Well, it's apples and oranges time again. This old chestnut keeps re-appearing in many forms, and from memory was first observed using microwave cavities.....

The velocity of light in a vacuum is the phase velocity, the speed of propagation of a selected point on the wavefront [ goes like ~ frequency/wavenumber ].

The velocity in the gas medium is the group velocity [ goes like ~ rate of change of frequency w.r.t wavenumber ] of a superposed set of frequencies.

By fiddling with 'dispersion' - the behaviour of speed with frequency - one can alter the 'shape' of that response and hence the value of the group velocity.

So yes, one can expand and/or compress pulse waveform shapes to get some interesting effects like that quoted. Thus

Quote:
the peak of the exiting pulse leaves the chamber about 62 billionths of a second before the peak of the initial pulse finishes going in


while quite true leaves out a few bits of crucial detail. Specifically the cavity properties are such that the outgoing pulse, while based upon the ingoing one, is not in fact the same one: it is a re-radiated version.

The apparent problem is a language one, in using the word 'peak' to imply a phase velocity measurement when in fact it is a comment on dispersion effects changing waveforms.

However if you examine the transition states between two such different waveforms, one will find the change in said waveform does not propagate faster than lightspeed.

Cheers, Mike.

NB As an aside ..... what is the propagation of light in a material medium but the capture and re-radiation of light by whatever charged particles are present, and with propagation via the vacuum between them? Like a bowling ball bouncing through a forest it's capture/bounce/radiate etc ........

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

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