A specific reference frame that describes its coordinates in a manner that does not depend on time and is isotropic.

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Fundamental paradox with Newton's Law of Gravity?

This is my first post here, but I've been struggling with this problem in my head since I studied physics at school when I was 14 (30 years ago!). There seems to be a fundamental paradox with ...
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2answers
59 views

Shape and even connectedness of accelerating components in SR is frame dependent?

In some inertial frame consider a disk of radius 1 lightyear at rest. Then along the edge of the disk there are some people in spacesuits at rest hovering right above the disk (which has negligible ...
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60 views

Derive the velocity-additon formula from the Lorentz transformation

In a Euclidian world the sum $s$ of two velocities $v$ and $u$ is so such that $s = v + u$. However, in the world of special relativity that's not the case. Instead, the velcity vector sum $s$ is ...
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1answer
66 views

Time dilation and relativity paradox? [duplicate]

I've come across a weird paradox that I can't answer, I will explain it via the following thought experiment: There is a space-train and an observer 1 light year apart with synchronised clocks. The ...
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1answer
35 views

How can we find velocity, acceleration etc, of a revolving particle with respect to an observer inside the circle(not at center)

A particle is revolving in horizontal a circle of radius $R$ with constant speed of $|\vec{v}|$ and constant angular velocity $\omega$. There is another observer standing inside the circle, at a ...
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2answers
142 views

Two sets of coordinates each in frames $O$ and $ O' $ (Lorentz transformation)

Suppose inertia frame $O'$ is moving at velocity $v$ relative to inertia frame $O$. Let the coordinate systems of $O$ be denoted by $(x,y,z)$ and the corresponding one on $O'$ be denoted by ...
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65 views

Lorentz Transformations understanding

I am wondering whether or not I fully understood what the variables represent in the Lorentz time and distance transformations. What I understand is: t′ is the 'proper time', the time taken to move ...
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3answers
256 views

A question in Special Relativity

In books the equation for length contraction is derived by supposing that the velocity of the spacecraft is the same for both observers. So the question is that, is the velocity really the same for ...
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3answers
137 views

Why can't we find a true inertial frame?

From one book, I read that if we release a ball horizontally on earth, its velocity does change in very accurate observations. If we track its motion, we get full information of its motion (incl. ...
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2answers
277 views

What does the first postulate of specially relativity really say?

I know these two versions of the same postulate is saying the same thing. But I failed to connect them. Please help me understand the links between them. version1 The laws of physics are the same ...
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1answer
69 views

Problem conserving 4-momentum at CoM frame in an inelastic collision [closed]

I am confused about the case where mass is not conserved in a collision (not due to relativistic factors). The center of momentum (CoM) frame is not the same before and after the collision. Let's ...
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65 views

Energy in the Relativistic COM Frame

I have been taught that in Classical Mechanics, the total energy of a system of two particles in the Centre of Mass Frame is given by $$ E_\mathrm{total} = \frac{1}{2}MV^2 + \frac{1}{2}\mu v_r^2 $$ ...
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81 views

Relative Lorentz factor for two shells

Shell 1 is travelling at a speed $v_1$ with Lorentz factor $\Gamma_1$, and shell 2 at speed $v_2$ with Lorentz factor $\Gamma_2$. Just before the two shells meet, the relative lorentz factor ...
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1answer
161 views

Non-inertial frames in Lagrangian mechanics?

Building on this Phys.SE post I am interested in how non-inertial frames can be considered in Lagrangian mechanics. My understanding is that changing the reference frame causes a transformation of the ...
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0answers
25 views

Traveling near the speed of light? [duplicate]

Suppose we can travel on a spacecraft near the speed of light, how long it would take for the person on the spacecraft to travel one light year, not to a person observing him/her from Earth, if there ...
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3answers
175 views

Isn't the aether existent?

Before you say I'm wrong consider this, Einstein is supposedly the first person to get completely get rid of the various aether models that were proposed. But didn't Einstein actually prove them right ...
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3answers
125 views

Isn't a physical frame of reference useless for calculating speed? [closed]

Please ignore relativistic effects and the effects of the expansion of space-time due to the expanding universe theory for the purposes of this question. Whenever someone asks what is the speed of X, ...
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3answers
184 views

If traveling at the speed of lights stops time, why does it take light 8 minutes to reach Earth?

I just learned that, according to Einstein's relativity theory, time reaches zero for an observer (light) when traveling at the speed of light, so everything is supposed to be at the same place in the ...
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0answers
19 views

I need a good book for learning mechanics in non-inertial frames [duplicate]

I'm studying classical mechanics, but without those stuffs Lagrangians and Hamiltonian mechanics...just Newtonian..the problem is a find hard to learn this non-inertial frames system, like ...
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1answer
52 views

Shooting a bullet in space [closed]

Imagine I was in space holding a gun and I shot a bullet from it. Do I go back? Or does the bullet move forward? Or both of us go in the same speed at different directions? Or what? Please Explain. ...
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1answer
41 views

Non-inertial system [duplicate]

Supposing I am in a non-inertial system and I don't know what forces are acting. How can I test EXPERIMENTALLY and in practice to be in a non inertial system? If I am in a system and I don't know how ...
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2answers
90 views

Is this an inertial frame of reference in relativistic context?

What I've learned from our special relativity lectures is that an inertial frame of reference in relativity is one that experiences no gravitational forces. Also, it is a frame where if a particle is ...
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138 views

Lorentz transformation of Gamma matrices $\gamma^{\mu}$

From my understanding, gamma matrices transforms under Lorentz transformation $\Lambda$ as \begin{equation} \gamma^{\mu} \rightarrow S[\Lambda]\gamma^{\mu}S[\Lambda]^{-1} = ...
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4answers
60 views

Can we observe two different events occuring at the same point?

I was wondering a situation. Suppose a train is moving with a certain acceleration. It turns on its front light at a certain time, and it's back light say t s after. But to a inertial, or non ...
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1answer
51 views

Newton's laws in non inertial frame

Suppose we take a two particle system in CM frame such that the particles are connected by a massless spring and a force $F$ is applied on one particle ($m_1$ and $m_2$. Let $F$ acting on $m_2$). Now ...
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1answer
96 views

Newton's first law of motion a corollary of second law? [duplicate]

His first law of motion states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. That means, ...
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1answer
43 views

Is distance always 0 relative to an object moving at speed of light $c$?

As I understand it, when an object is traveling at the speed of light, relative to itself all travel is instantaneous and the distance is zero. If a photon traveling from the sun was aligned with the ...
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2answers
85 views

The invariance vs constancy of the speed of light in vacuum

This is perhaps as much a question of semantics as of physics but it is something I have been thinking about recently and was wondering if anyone else had a perspective on this. Now, it could be that ...
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2answers
1k views

Is the Earth the center of the Solar System? [duplicate]

Alright guys, so I attracted you with the title. Now, to preface the question, I am fully aware of the work of Copernicus, as well as the concepts of Heliocentrism and Barycentric Coordinates. I have ...
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1answer
55 views

Is gravitation time dilation simply c/v?

Recently, I've been very interested in forms of time dilation. I'm relatively new to relativity, so I apologize for any stupid mistake I may make. I was messing with the equation for gravitational ...
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4answers
1k views

Why the speed of light in vacuum is same in all inertial reference frames? [duplicate]

If Cathy’s velocity toward Bill and away from Amy is v = 0.9c, Cathy finds, by making measurements in her reference frame, that the light from Bill approaches her at speed c, not at c + v = 1.9c. ...
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1answer
56 views

Derivation of length contraction from lorentz transforms

i have struggled to understand how length contraction is derived. My lecture book says: length in frame S is defined as $L=x(b)-x(a)$ and in S' as: $L'=x'(b)-x'(a)$ transforming $x'(b)$ and $x'(a)$ ...
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1answer
76 views

How fast do you have to be traveling in order to travel one light year in one year due to relativistic effects?

My apologies if my understanding is incorrect, but I believe that as you approach relativistic speeds you experience time dilation as compared to an outside observer. So taking into account this ...
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1answer
46 views

How to combine Lorentz factors when boosting twice?

The problem came up when I was trying to solve the classical problem of a wire with current due to which a charged particle experiences a force. This force should depend only on the lorentz factor ...
3
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1answer
57 views

Special relativity kinematics problem [closed]

I have this problem in SR kinematics. a spaceship travels near earth at c/2. it shoots off a light-ray at 45deg to its direction of travel (measured in its own ref frame). What is this angle in the ...
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2answers
71 views

Lorentz force Law

I want to ask a fundamental question about Lorentz force equation. Why is it important to incorporate both electric and magnetic forces into one single expression? I know magnetism is electricity's ...
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1answer
159 views

What would happen to the human body if we went almost at the speed of light? [duplicate]

If we were to travel almost at $299\,792\,458~m/s$, or the speed of light, what would happen to the human body? Would the human body stay the same or would there be consequences that would harm the ...
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1answer
58 views

Traveling near the speed of light

If I travel near the speed of light, form a stationary observer perspectives, I will take 1 year plus to travel 1 light year, but in my perspective, would I take less than 1 year to travel to that ...
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1answer
88 views

Is cause-effect always preserved in relativity?

I guess most of you are familiar with the "paradox" of the train passing through a tunnel smaller than itself on a speed close to the speed of light and 2 guillotines (1 in the exit and 1 in the ...
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1answer
70 views

Is Lorentz transformation applicable of light itself?

I've just studied Einstein's Special Theory of Relativity and have followed most part of it. I was just wondering that whether the equations of Lorentz transformation are applicable on light? i.e. can ...
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2answers
61 views

Frames of reference and why are they different

Here is a quote from "The Elegant Universe" by Brian Greene. Imagine two countries that have been at war are sitting down to sign a treaty ending hostilities while traveling aboard a train that is ...
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3answers
76 views

Our speed and direction by comparing the speed of light?

If the speed of light is constant no matter the speed of the source, shouldn't we be able to know the direction and exact speed we are going relative to the absolute 0 in speed? If a photon is sent in ...
12
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5answers
630 views

How does one determine an inertial frame?

How does one determine whether one is in an inertial frame? An inertial frame is one on which a particle with no force on it travels in a straight line. But how does one determine that no forces are ...
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0answers
102 views

Absoluteness of Simultaneity?

Here is a very good proof that simultaneity is absolute, not relative. The question: Is this proof wrong, or is Einstein? Can you prove it? What is the mistake in the proof, if any? If there is none, ...
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5answers
3k views

Paradox in special relativity

Yesterday we started relativity on our physics class, and my professor taught us a few concepts. We did some examples on how things changed by looking them from different reference systems, and a ...
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2answers
185 views

Understanding Mach's principle: What does it answer?

What is the question that Mach tried to address in his principle? I mean, we know how to detect the inertial and non-inertial frames (by Newton’s law). Once this is understood we also see that due to ...
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1answer
38 views

Force on a moving charge in relative frame

Consider a particle of charge $q$ moving at velocity, $v$, enters a magnetic field $B$ which is perpendicular to its motion. Now consider two observers, one stationary and the other moving at the ...
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How to add together non-parallel rapidities?

How to add together non-parallel rapidities? The Lorentz transformation is essentially a hyperbolic rotation, which rotation can be described by a hyperbolic angle, which is called the rapidity. I ...
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99 views

In special relativity, is it correct to say the speed of a body B relative to A is the same as measured by every observer?

Here, two objects A and B are moving relative to each other. I use the Einstein velocity addition formula $v = {v_1 + v_2\over 1 + {v_1 v_2\over c^2}}$ to calculate the relative speed between A and ...
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4answers
89 views

Sun and planets orbit each other

Do not the planets and the Sun revolve in orbits around each other and the shape of the orbit depends on where the center of gravity of the system is? The greater the mass of the Sun, the closer the ...