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-2 votes

Intuition for multiple temporal dimensions

I have been a self-guided student of theoretical physics for over 30 years. I don't have any formal training. I have been working on a model of our universe ever since I purchased and read Dr dr ...
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2 votes
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What does $\delta/\delta t$-derivative represent in tensor calculus?

If $t$ is parameter which varies along some time-like or null geodesic, and say the tangent vector at each point on the geodesic is given by $V^a=\frac{dx^a}{dt}$, then the acceleration vector is ...
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3 votes
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How does the scale of a cataclysm determine if we can look beyond it?

Cataclysmicity is not a physically measurable observable. That part of the quote is not physics. The first sentence should refer to the theories of cosmology, plural possessive. Cosmology is a branch ...
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  • 8,643
1 vote

Are time and length independent or can one be derived from the other?

"Time" is not a quantity at all, it is a coordinate similar to "north", "east", or "up" (or "x", "y", "z"). What Rindler is saying ...
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5 votes

How fast would a clock falling into a blackhole tick relative to the reflection of a clock stationed far away?

If you drop it from rest at radial coordinate $\rm r=r_0$ the free fall velocity at $\rm r=r_1$ is $$\rm v=c \ \sqrt{\frac{r_s \ (r_0-r_1)}{r_1 \ (r_0-r_s)}}$$ which in the limit of $\rm r_0=\infty$ ...
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  • 7,372
2 votes

The speed of time

Are time and gravity the same thing? No, they are not. Could there be a speed of gravity (cause and effect)? Gravitational waves travel at the same speed as light. In quantum theory both as ...
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1 vote
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How to find time taken for a faster object to cross a slower object of same length, both moving parallel to each other in the same direction?

When solving physical problems it is essential to draw diagrams. This helps to develop a concept in your mind (especially when having no idea yet about the solution). Do this before writing down any ...
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0 votes

How to find time taken for a faster object to cross a slower object of same length, both moving parallel to each other in the same direction?

Here you're only trying to find the time taken by this object to cover a distance equal to it's length. So, time=length/speed. Have you been given the speed and length?
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1 vote

How can a time-dependent gravitational field be conservative?

Conservativeness of a field is defined based on its state at single point of time. The closed path trip of the particle is only imagined, it is not supposed to take non-zero time. So it makes no sense ...
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0 votes

How can a time-dependent gravitational field be conservative?

Let't consider 2 point particle graviting the one around the other. Can that gravitational field be considered conservative? I can go from A to B and then, after a time $\Delta t$ come back to A with ...
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  • 7,265
0 votes

Recordings of journey traveling near speed of light

Each recorder shares proper time with its corresponding clock, so both sets record and show the same amount of time during playback. The clocks themselves though, after luminal travel, would show ...
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-1 votes

How can time go in different directions in the Universe?

If time represents all change in the current state of the universe, then any change in the relationship of variables in spacetime could be interpreted as a change in the direction of time. Example - ...
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1 vote

Is this line of thought compatible with current physics thinking?

Statement: "The closer we get to the max speed of light, the faster time is moving from the perspective of the people "stationary" on Earth." Not correct, Time does not speed up, ...
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0 votes

Time dilation - do all moving clocks run slower?

So $A$'s clock is going to tick off a time of $$t_A=t_0$$ which is the proper time between the two relevant events because $A$ is at rest. As $B$ approaches the planet, he has been moving at $\beta$ ...
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1 vote

Time dilation - do all moving clocks run slower?

If person A on Earth looks at his own clock A', he sees his proper time, because he is at rest with respect to his own clock. Similarly, if person B on the rocket looks at his own clock B', he sees ...
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0 votes
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Deriving the age of the universe

While doing these types of calculations always use integral calculator site (https://www.integral-calculator.com/) There’s a trick that always works while taking these kind of integrals. Write down ...
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0 votes

What makes energy "the" conserved quantity associated with temporal translation symmetry?

The answer is that the statement that there is such a thing as "the" conserved quantity associated to temporal translation - or to any symmetry - of a dynamical system, is simply wrong: ...
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0 votes

What makes energy "the" conserved quantity associated with temporal translation symmetry?

I think this is an interesting question. One should keep in mind that the symmetries are in the action S, which is in many cases composed of dual Fourier pairs (position and momentum, or energy and ...
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1 vote

Confusion with the variational operator $\delta$ and finding variations

Yes, that happened. I guess you meant $$ \delta f = \sum_i \frac{\partial f}{\partial x_i} \delta x_i $$ on your third equation. Also you've implicity fixed inital $t_0$ and final $t_1$, so that your ...
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  • 179
0 votes

Confusion with the variational operator $\delta$ and finding variations

If the Lagrangian only depends on time through $X$ or $\dot{X}$, then we say that the Lagrangian has implicit but not explicit time dependence. So in your example, we would write \begin{equation} L(X, ...
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1 vote
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Quantum Time Crystals

He is referring to a more precise definition of order parameter. The idea is to capture spontaneous symmetry breaking: the ground states of the system are not individually invariant under the ...
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2 votes

What makes energy "the" conserved quantity associated with temporal translation symmetry?

There are nice answers already. I just want to add one small observation. If $H$ is the energy, ordinary time is defined by the Hamiltonian flow with $H$, so observables evolve according to $$\frac{dO}...
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0 votes

How does the flicker fusion threshold prove time perception?

I am also interested in this subject. Not only is the flicker fusion an indication of the relative speed of processes in differing species, but also the metabolic rate, life expectancy, heart beat ...
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13 votes

What makes energy "the" conserved quantity associated with temporal translation symmetry?

The OP's question is basically stating that in a system with time-translation invariant dynamics, we can define a conserved quantity by arbitrarily assigning a real number to each orbit; when the ...
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  • 4,605
7 votes

What makes energy "the" conserved quantity associated with temporal translation symmetry?

For what it's worth, OP seems to be mischaracterizing Noether's theorem by seemingly ignoring one of its main assumptions: That the physical system is equipped with an action formulation $$S~=~\int\! ...
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  • 167k
2 votes

What makes energy "the" conserved quantity associated with temporal translation symmetry?

If I understand the question correctly, then a flow $\Phi^t$ uniquely determines a Hamiltonian vector field $\mathbf X := \mathrm d\Phi^t\big|_{t=0}$. Such a vector field can be written as $$\mathbf ...
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0 votes

How does time work if the universe is the surface of a hypersphere

There is a theory in which our 4 dimensional universe is the boundary of a 5 dimensional hyper-sphere. One needs to send the radius of this sphere to infinity. This theory predicts the emergence of a ...
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12 votes

What makes energy "the" conserved quantity associated with temporal translation symmetry?

What is special about the conserved quantity $Q(x, p) := \frac{1}{2} (x^2 + p^2)$, when also the quantity $Q_2(x, p) = \sin(x^2 + p^2)$ is conserved too, by the same temporal translational symmetry? ...
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  • 7,265
0 votes

Notion of Present

The notion of 'the present' presupposes a notion of simultaniety and Einstein pretty much deconstructed this notion in his paper on special relativity when he promoted the constancy of the speed of ...
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