Nah, Syd just wants coolness, the kind you get by putting a playing card into your bike spokes to make it sound like a motorbike. ;)
He could just take his car speedometer, scratch out "km/hr" and write in "c", and his commute could be at 100c!
Cheers
Phil Hobbs
On a recent gizmo I put an audio amp with a gain from 0-11. So marked on the panel. (No customer comments yet)
George H.
The spinal anaesthetic hasn't worn off yet. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
No need to be petulant, just because you hadn't considered the issue and jumped to an incorrect knee-jerk response :-)
Cheers
-- Syd
Silly me, thinking you wanted an accurate measurement!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I wouldn't expect any comments. Audiophools *expect* their amplifiers to go to 11.
Indeed. I suspect the OP was only interested in engaging in sophistry rather than understanding relativity so we were wasting our time.
If you do come across the paperback with that proof in the form I described I would very much like to find it again - as a book to recommend to people who are struggling to grasp what relativity means.
Too often in engineering courses it is taught deus ex machina with the transforms not properly or convincingly derived for the students. This is a pity since making the laws of physics the same in all inertial frames is a *very* compelling symmetry argument.
-- Regards, Martin Brown
Maybe Gamow's "Mr Tompkins In Wonderland"?
Cheers
Phil Hobbs
Not at all. The discussion was very useful, this had been something I was unsure of for some time, but I now conclude that:
1) A 'conventional' onboard speedometer timing previously laid out mile markers using the spaceship's clock *can* indicate more than c. 2) This indication is not a meaningless number, for example, it could be used to very easily calculate the onboard time remaining for the spaceship to reach a destination with the distance scaled off a printed star chart. 3) None of this violates relativity, nor is it intended to. 4) Some people can't or won't think beyond what they've learnt.You may well disagree with 4. Does anyone still disagree with the first three?
Cheers
-- Syd
I make no claim to have a full understanding of relativity, but I basically agree with your points. However, it has been shown that the conventional speedometer is based on a fallacy. This brings up another point, which is how the instrumentation in such a spaceship could determine its velocity and calibrate its clocks to correspond to what would be observed from the "relatively stationary" earth and other objects in that reference plane.
The traveler knows the distance between certain identifiable objects (mile markers) as they appear from earth's reference plane. So, if he counts
186,000 mile posts in a time "t" as measured by his internal clock, he will think that his speed is 186,000/t relative to earth. But his speed is such that his time has slowed to half that on earth, his relative speed would be 186,000/2t. Without going through the math, there would be a point where his speedometer would read a multiple of "c", perhaps 10c, while on earth the speed would appear to be 0.9c.It seems that the traveler could use a similar conversion to determine earth time and speed. But I think the spaceship speedometer would correctly determine the arrival time as experienced by the traveler. So at very near the speed of light, his travel time would appear to be just about instantaneous, while from earth it could be many years.
Another way to determine the speed of the spacecraft might be to keep track of the acceleration. In the absence of gravity, an acceleration of 1 G would provide a good estimate of speed up to some fraction of the speed of light. But as speed approaches relativistic levels, the traveler's clock will slow down, and if that is taken into account, the speed must converge to c. However, momentum would increase linearly with constant acceleration, such that the mass will increase. Of course, the spacecraft would need to convert mass to energy in order to continue accelerating, so the mass will be depleted. However, since the mass is also increasing, and if it can be converted to energy for propulsion, the two may tend to somewhat cancel.
Like I said, I'm no expert, but this seems to make sense to me. But I enjoy such discussions.
Paul
You got the equation wrong the time would be 1/2 t so the math would be
186,000*2/t. Time slowing means the traveler will see the trip take *less* time, not more.Yes, that is right, just look at the twin paradox, which is what you are summarizing.
The traveler won't know he is feeling relativity. He will feel 1 G for all time.
I wouldn't try to bring any practicalities into this such as "how does he continue to accelerate or how does he get the fuel? Imagine he is constantly refueled on the trip by finding and exploiting fuel reserves traveling at his speed.
How about two travelers moving apart? Both seem slowed relative to the original frame of reference, but they still see each other as even more slowed.
-- Rick C
That's an interesting point. If it takes X gallons of rocket fuel to travel some light years, and from the traveller's POV his speed is such that the journey only takes a few months, say, then his fuel pump (for example) will need to be huge to pump all that fuel in such a short time.
Cheers
-- Syd
Fuel is only needed for acceleration and deceleration. Once you attain a certain speed in space, with a near perfect vacuum and negligible effects of gravity, you can travel any distance with no expenditure of fuel. The problem is that it takes a lot of fuel to get even close to the speed of light, and then much of the energy is used to increase mass.
It may be possible to se a "gravitational slingshot" to obtain energy and accelerate a space ship by using the gravity of a planet or other massive object, as well as its momentum.
Another source of power for refueling enroute is solar (or stellar) energy, which entails getting close enough to a source of light (or having a large enough solar array) to replenish some of the fuel in the ship. But it is not very efficient with today's technology to store such energy and then use it for propulsion in space.
I still think the spacecraft's speedometer (or the traveler's computation of speed) based on earth's reference point could read many times the speed of light. For instance, he may pass close to two stars on his journey that are known to be, say 1 light-year apart. But if he is traveling almost at the speed of light, he might see the stars pass by in just a day, according to his clock, which has slowed down by a factor of 365. So he would see it as
365 C. Of course, the distance between the stars, and their diameter in the direction he is traveling, will appear much less, more like a flat disc of thickness 1/360 of normal as the object is approached. However, AFAIK, as he passes by and observes the star at right angle to his trajectory, it will appear normal. And then, as he looks in the rear view mirror, I think the star will appear to be stretched out by a factor of 360:1.Perhaps the degree of perceived flattening and elongation of objects known to be spherical, could be used to determine speed?
Pal
(snip)
Yes, it makes sense. But gravity alone can't do it, I think. The planet must have some velocity in the direction you wish to go. Otherwise, the space ship will slow (due to gravity) when it departs as much as it gained on approach (due to gravity).
That makes no sense at all. Again, you are mixing two perspectives.
-- Rick C
Is that illegal?
But anyway, putting it another way, if his journey time is only a few months, he only needs supplies for a few months, so his fridge can be smaller than that on a slower craft. I don't think that's mixing anything up.
Cheers
-- Syd
There are no laws, but it won't give you meaningful results. From the perspective of the traveler, he is burning the fuel just as he expected which will be a high enough rate to get him there in the time he expects. But he can't expect for the trip to take longer than it will from *his* time frame.
The other observer will see the ship approach the speed of light but never exceed it. But correspondingly, the fuel will burn slower, but the trip takes longer.
What you seem to be saying is that the traveler would expect to see the same slow burn speed that the other observer sees, but only for the shorter time frame.
No, but that applies to sailing ships too. Slower trip, more supplies.
-- Rick C
one that times wheel rotations would not, due to length contraction.
chronographing milestones seems unconventional to me.
-- This email has not been checked by half-arsed antivirus software
Assertion don't prove nothing. The wheels on the bus go round and round.
'Chronographing'? Are you in marketing or something?
Timing mileposts is no different from timing wheel rotations. There are a fixed number which will be passed.
This is done and dusted, the spaceship's speedo can read >c if it relies on pre-positioned mile markers passed as timed by the ship's clock. Or wheels on the road, same thing.
Cheers
-- Syd
That is not a strange thing to insist on. Suppose I drive 100 km/h and the hospital is 150 km away. It will take me 1.5 hour *as seen on my own watch*. Why would I measure that differently? Or even differently if I go really fast?
So it is the practical km/h that one uses to find out at what time one will arrive. Time is relative so in what frame? Well of course "my" frame. So yes, you see a speed of 1.5 C and low and behold, after your watch indicates one year passed, you're 1.5 lightyear ahead. That is what you want to see on your speedometer.
The OP had a well posed question. If you understand physics well enough you realize that light speed is in fact an infinite speed. Photons get to the other site of the universe in less than 10^-100 nanosecond.
Groetjes Albert
-- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst
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