Relativity

Hi friends, Once again I got this situation in my head. Let there be a metal rod of original length l, and the rod material has a coefficient of linear thermal expansion of a. Let this rod travel towards a star at a speed v, very near to the speed of light. Let the change in temperature of the rod be T. Then new length after thermal expansion l' = l(1+aT). But there is also length contraction. So the real length l" = l'/y = {l(1+aT)}/y , where y is the Lorentz factor. Am I right in this calculation ? Or, am I missing out some other factors ?

Do we get different curved geometries in all Spaces that have different forces(= fields?) present ? I have never heard of space time curvature being applied to other areas like magnetism but are there also geodesics in magnetic fields, as an example and is it right to also talk about a spacetime curvature in that context as well? If one needs to calculate the path of an incoming object that was subject to the Earth's magnetic field is it possible to do so (ignoring gravity) in terms of it following a "magnetic geodesic" ? Does such an object ,in a magnetic field undergo acceleration ? If it does, does that say it is not following a geodesic?

If an expanding wave of light is viewed as a sphere which increases in size and propagates away from the source, is it fair to say that a portion of the wave actually moves at 2c with respect to a corresponding portion of the wave expanding in the opposite direction? Is that true and does anything follow from that observation? Or is it not true and is this an example of how relativistic speeds do not add linearly ? Or is it perhaps an example of ,as I have heard the idea that you cannot use light as a frame of reference?

According to Einstein's Special Theory of Relativity, time passes slowly for an observer when the observer is near a gravitational source. So, if there are two observers, time passes slowly for the one whose distance from the gravitational source is less as compared to the other. So, time dilates for the lower observer in relation to the upload observer ( considering the case in a gravitational potential well). However, if the two observers are not allowed to communicate or see each other, they would never realize the time difference. The direct result of the gravitational time dilation is gravitational redshift. For an upper observer, time passes more quickly than the l…

I would like to ask you all a question about Photons and the expansion of the universe, and how they relate to one another. I thought about it after a long talk with a friend about how photons react to the universe, and how they basically don't experience time, since they are in fact traveling at the speed of light, where the time dilation is close to infinite. Then I wondered about what exactly happened after the big bang? We have the microwave background radiation that we can observe, and red shift and blue shifting of bodies of light traveling towards and away from us, that I understand, but, here's the question that got me waking up at 5 in the morning: where exactl…

Can it be tested as to whether the theory of GR still applies in the extreme situation where two bodies (not particles) interact at such a remove from sources of mass-energy that we can ,for all intents and purposes regard them as constituting the entire universe? If we consider only the mass-energy bound up in the two bodies in question is it known/expected that they will curve spacetime in the same way as they do when they are just a part of the overall system of macro objects? It is not possible is it that GR will lose its applicability (or need to be tweaked) as such an extreme situation is approached?

Hello, sorry if this question is out of correct forum or seems silly, I am relatively young (13) and decided to learn Physics but since I am self-teaching I am finding it hard to grasp certain concepts since I am self-teaching myself. When it came to Planck's Constant and Photons I got a bit confused. The book I am reading just put the equation e=hc/wavelength but didn't explain how to do the equation so I went online. After going on http://www.pveducation.org/pvcdrom/2-properties-sunlight/energy-photon I entered all the numbers into my calculator, after doing 6.626x10^-34 (which is Planck's Constant) x speed of light, I got my answer to be 1.9864x10^-25. Then it said t…

An "event" is a point on the Space-Time graph where something occurs . Or is it? Is it a point where something may occur but may not? (Are there [x,y,z,t] s where nothing happens? ) Also, I have an (erroneous?) idea in my head that the Space-Time graph can ,if drawn in sufficiently fine detail model every macro level interaction between things in the real world. Is this a misapprehension ? Is the name "event" in the Space-Time graph (or manifold) simply a description of when and where something might occur but it does not describe the occurrence in its entirety? So "event " is only a partial description of what is happening? If th…

Is the gravitational attraction of a massive body greater depending on its temperature? Does the energy in the heat of the object contribute to curving space-time around it?

Does a clock measure time, or does a clock measure itself? To me it makes sense that gravity simply affects the clock in these experiments, gravity isn't effecting "time" itself.

I am not quite sure this should be in Relativity and I am not quite sure why I am asking the question .I am "fishing" a bit ,perhaps to flesh out my ideas but this is the question. Suppose we are in London and need to be in Glasgow in a week's time , what is the most energy efficient method of getting there? (obviously the method of transport and all other environmental factors are the same no matter which route is taken) So ,the first option could be to leave directly ,arrive at Glasgow in 6 hours and remain in Glasgow for 6 days and 18 hours. As an alternative itinerary we could also leave at once , go to Norwich in three days (traveling very …

Suppose we have two events in Space-Time and they are (fictionally): (1) In AD 0 Marcus Suetonius is walking his dog in Londinium (2) In AD 2000 Ray Davis is having a coffee in a cafe near to the same place in London. QI Can these two events be modeled as members of a set of Space-Time events in a 4D manifold? Q2 If they can, are they joined** in this manifold by the entire set of events that can both have been caused by(1) and have been able to cause(2)? Q3 If this manifold model can be built it it necessary to choose a frame of reference at the outset? Will Hastings 1066 be as good as any? Q4 Is there a chain of Space-time events connecting (1) and (2) ? In fa…

In the philosophy forum we are discussing interpretations of the car scenario that was earlier discussed in this forum. The car has two synchronized clocks. While rehashing it, I turned it "on the fly" into a twin scenario by letting the car do a turnaround. To keep it simple, a let the car take a sharp turn without changing speed. Without much reflection I stated that after turnaround the car's "reference system has been messed up: the speed of light doesn't seem the same anymore in both directions" because the clock synchronization was done for a different inertial reference system. Mordred added that "A change in direction results in loss of synchronizatio…

I have been searching for the "author" of the rubber sheet analogy for the curvature of Space Time and the question has arisen as to whether there exist better analogies. I can well imagine that all analogies are likely to be flawed and misleading to one degree or another but perhaps they can be educational provided (as is not the case with me personally) the mathematical model is well embedded in the mind of the student. Be that as it may ,I have come across this alternative analogy. Are there other ,better ones? http://www.academia.edu/815814/Reflections_on_a_Variational_Principle_in_Space_Gravity_and_Light on page 6 they give an analo…

Not strictly a physics question, more history of science. But this has come up in a few threads where people have mentioned "Einstein's rubber sheet model". I have read little of Einstein's original writing but I didn't think he came up with this analogy. Does anyone know where it originated?

This gif was posted by a fellow member in another thread My question is: If you look carefully, some dots are crossing the diagonal lines. As explained above, the events that pass the two diagonal lines in the bottom half of the image (the past light cone of the observer in the origin) are the events visible to the observer. Does that mean that the dots as seen by the traveler suddenly appear as coming from nowhere? That events pop out? As if coming out from the unobservable part they appear suddenly? I hope that my question is clear.

A key premise of relativity is that there is not a fundamental frame of reference that is above all other frames of reference. But this seems to lead to a logical conflict when explaining how clocks lose time when they travel in a round trip (the travelling twin scenario). Please can the steps of how the travelling clock loses time with respect to the stay at home clock be walked through, with particular focus on why the following is not a problem... A recent post discussed travelling clocks and rulers. The conclusion with regards to rulers, was that a travelling ruler does not physically change its length compared to a stay at home ruler. Although each frame…

I just want to know about how to store thunder lighting in copper pieces... Its all i think that it is useful in Random power to use the process for charge the neuclar power station of weapons....Is that all possible...??

it is time to share the concepts that i had accumulated since few months past , related to the photo electric effect. which was explained by the Enistein nearly a century ago but i felt that his version is lacking little informational concept that would explain the phenonmenon more precisely so inshallah sooner i will share those concepts on this forum so that every one would be able to explore those concepts and i hope that my version will become more familiar to people which however is same as Enistein had mentioned regarding the concept, but i had just structured it in little distinct way which can be under stood by considering both wave as well as particle nature of…

This thread is about Langevin's The Evolution of Space and Time Here in English https://en.wikisource.org/wiki/Translation:The_Evolution_of_Space_and_Time And in French https://fr.wikisource.org/wiki/L’Évolution_de_l’espace_et_du_temps Quoted from page 45 (enhancing by me) The first bold part is understood by me as the contrary of the second bold part. (I checked the original text in French and it is not an error in translation) Where is my error?

So i had to write an essay on relativity and something's really bothering me: Why do I find every source saying "the moving clock ticks slower"? My issue is that i find it hard to believe that if time is dilated to it, then it should be moving it's mechanism slower. I think even though time is being dilated, it ticks just as fast as the stationary clock, when compared afterwards they show different times because the moving clock ticked for less time than the stationary clock and thus seems as if it ticked slower. Please someone tell me which one's right and why.

And with this comment we are back to the beginning (the rulers discussion) The clock "does" nothing, because velocity is relative. IOW all different observers from different frames will observe the clock ticking at different rates. Like the ruler that remains the same length for the traveler who has the ruler at hand, the clock doesn't change rate for the traveler that has the clock at hand. So, the clock "does" nothing, it continues ticking as usual. Anyway, the clock cannot tick at multiple rates just because there are multiple observers.

If a person flies off in a rocket then returns, that person has aged less than the starting point? If two people fly in opposite directions and return they are both younger than the starting point? Because they have travelled away from each other at twice the speed/distance as from their starting point, is not one then younger than the other?

I am a firm believer that the further you look into space with a telescope the older the transmissions of light one can see, and therefore shall you be in a distant galaxy and you observe Earth with a very powerful telescope that you may be able to see Earth during, perhaps say, the Jurassic Period. But it wasn't until I began to become involved in optics that I began to have some questions. I know that light travels ~186,000 miles/second. I also know that the larger the aperture, the more light is able to be collected. But the speed of light is constant. On the face of things, it began to become apparent to me that the light hitting the telescope l…

Based on the widely diverse solutions to the twin paradox, Twin paradox solutions almost seem like an opinion poll and they seem to disagree on certain aspects, so I'm lost on what's the most accepted. Five questions on SR: 1) is acceleration ≡ gravity still the most accepted solution for the twin paradox? 2) Which is more accepted: Clocks moving towards observer run faster or slower than the local clock? 3) Is there any proof that shows that length could not exceed proper length regardless of direction of movement (towards/away)? 4) What are the consequences of the invariant spacetime interval? 5) is there a specific finding or proof that triggered controversy?