# Tag Info

0

That discussion is about a spherical shell and does not apply to the Earth nor to the sun. In the latter situations assuming uniform mass distribution we know that time is dilated by $t(\infty)/t(r)=\sqrt{g_{00}}=\sqrt{1 - \frac{2GM}{rc^2}}$, where $r$ is the distance from the center. For a spherical SHELL however we have to go back and forth between the GR ...

1

In a comment Kyle points out the question Does strong magnetic field cause time dilation?, which is closely related to your question. However it isn't a duplicate because you are specifically asking whether experiments have been done, not whether the effect theoretically exists. Theoretically we would expect a magnetic fied to contribute to the curvature of ...

0

If everything were at zero temperature you probably* would not be able to distinguish between the past and future. Mathematically time would still exist, in the same way that spatial directions still exist on a completely featureless plane, but since it would not be measurable (even if there were something around that could do a measurement!), it is ...

0

No. In fact the official definition of the second is: The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom at absolute zero. So time is still alive and kicking at absolute zero.

2

Your idea does not seem to work if you have two particles at different temperatures. Assume you "stop" one of them but not the other. Then does the time slows down for only one particle and not the other? or how would you explain that?

2

is there any requirement to determine (and possibly correct for) the perturbation, or "shift", of any and all primary frequency standards, besides the described "shift due to ambient radiation"? Yes. These are called "systematic errors" and they are the order of business pretty much all day, every day, at the metrology labs that implement frequency ...

10

This is an area rife with potential misunderstanding, so we need to be absolutely clear what we mean. Suppose I take a ruler and a clock and I use rulers to mark out $x, y, z$ axes in space and the clock to note the positions of events in time. Assuming spacetime is flat, I now have a universal coordinate frame that everyone who is stationary relative to me ...

2

Why a black hole? Try earth, this very experiment has been done with precision atomic clocks, on at sea level and one in the mountains! When comparing the times shown on the clocks later, the one that was on the mountain advanced faster (cf. experimental confirmation of gravitational time dilation)! This effect even has to be considered for the precision ...

2

First off, traveling at constant velocity in flat spacetime is not the same as traveling g in a uniform circular motion. Quite the contrary, free falling towards the gravitational source is actually equivalent to moving with constant velocity in flat spacetime. This is so because the objects are following a geodesic path defined by the geodesic equation. I ...

0

I found a nice discussion of this from several years ago at physicsforums. Inside, Ben Crowell makes an argument that does in fact use time dilation: if you're willing to accept that the properties of a massless photon are the same as the $m\rightarrow 0$ limit of a massive photon, it's easy to see the decay rate has to be zero. One way to see this is that ...

0

I think it might help if you go back to the physical definition of time: "Time is that which is shown by suitable clocks". Period. Full stop. End of transmission. What do I mean by that? I am trying to point out that statements like "time flows" are analogies that were attached to the physical definition of time for no good reason other than to make ...

3

The answer is "no", not as a straight 1-body -> 2-body decay. Proof: let $E_\gamma, E_1$, and $E_2$ denote the energies of the initial photon and the two daughters, and define $\vec{p}_\gamma$, $\vec{p}_1$, and $\vec{p}_2$ similarly for their momenta. By conservation of energy and momentum, we have $$E_\gamma = E_1 + E_2,$$ $$\vec{p}_\gamma = \vec{p}_1 ... 1 You are confusing time with the flow of time. Time is just a coordinate like the spatial coordinates, that is we label spacetime points with four coordinates (t, x, y, z). Indeed, in relativity (both flavours) the time and spatial coordinates get mixed up so different observers will disagree about what is time and what is space. But the obvious thing ... 0 Newton actually expressed his 2nd law in terms of force and momentum as Joseph wrote in his comment to your question. But considering causality then the second law is better expressed as$$p(t)=\int F(t)dt$$In other words force comes first, leading to motion. By considering the case where mass is constant$$ m \frac{d^2}{dt^2}x(t)=F(t)  where x is the ...

0

Suppose before time t=t0 the net force was zero but at time t=t0 the force is non-zero. At what instant is the acceleration gonna be non-zero ? Is it gonna be at t=t0 too ? Remember that, if we're talking instantaneous measurements, your target can have a non-zero acceleration and still have zero velocity. As pointed out, in the real world your target ...

8

In the real world, you push the atoms in the back end of the object, which push the atoms in the next layer, etc. This means that the front end of the object won't start accelerating until $t = t_0 + \Delta x/c_s$, where $\Delta x$ is the length of the object and $c_s$ is the speed of sound in the material of the object. If you consider the object to be one ...

0

Galileo dropped the notion of absolute rest for reasons he described in a dialogue on two world systems; this also meant it wasn't possible to hold onto a notion of absolute motion (the notion was in his time seem as part of Aristotelian Philosophy; though Aristotle himself didn't hold it). Newton then described space and time through his notions of ...

0

How about: Mathematically it's an interesting thing to do and a fairly obvious direction for generalizing the Galileo group, as I discuss in my other answer to you - it leads to the nontrivially signatured orthogonal groups; Experimentally we have heaps of evidence for relaxing the absolute time postulate; Watch this video: "The Illusion of Time" by Brian ...

0

Both observers see the other approaching at 99% of light but since observer 1 is the reference frame that accelerated, and changed it's behavior of motion, it is the reference frame that will have experienced less time than observer 2 during the duration of it's travel. The change in motion (acceleration/deceleration) is what changes the rate at which a ...

1

Here are the three primary definitions of time in 3 prominent English language dictionaries: American Heritage Dictionary also thefreedictionary.com 1a. A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future. 1b. An interval separating two points on this continuum; a ...

1

In everyday (or casual) use "time" is often (mis-)taken to mean duration, or a coordinate assignment to indications or entire events ("coordinate time"). In contrast, the current, correct and careful meaning of "time" in Physics is based on Einstein's definition of "time" as "the position of the little hand of my watch"; i.e. generally as any one ...

2

The oldest perspective is the philosophical one established by Aristote; modified by Mach and then Barbour Time is an aspect of change (ie motion) There is the mathematical perspective Time when mathematically conceived is just a parameter in the equation. This in fact has nothing to do with time - it's purely formal Physically there are a couple ...

2

In layman use, across the world (ignoring time zones), someone who is walking observes the same time as you. In physics, however, that person has his/her own time, relative to that person. In classical thermodynamics, time is the same as layperson's time. It is just described in a different way. Quantum mechanics doesn't say that time doesn't exist.

0

[...] neither country's delegate wants to sign the treaty before the other delegate and thus, a simple system is devised to ensure that both delegates sign the peace treaty simultaneously. The solution involves setting a light bulb at the center of a table in such a way that the light bulb is exactly between the [two] delegate[s ...] the light bulbs ...

0

As the other answers point out, there is no "right" or "absolute" frame of reference for measuring time. But that does not answer your question: Is there a way to measure the passing of time for this object? It turns out there is. Oscillations in the orbits of electrons depend only on the material, and in fact our clocks measure the passing of time by ...

1

There is no reference object that transcends all inertial frames of reference. Everything in this universe has an inertial frame of reference, and none of them are privileged. If there were any object that existed independently of the relativistic effects of acceleration/gravity or of observer movement, then theoretically it could provide a reference to ...

15

In relativity there is no standard-clock that tells you which time is "right". That's the point about relativity. There is no need for a absolute reference to compare with. Everything is just the way you observe it (that is, relative to you). Things may slightly differ from observer to observer but the qualitative behaviour stays the same just as classical ...

0

So as we from the outside of the black hole observe matter approach the event horizon, we will see time slow for the falling matter. Conversely, an observer falling into a black hole would see external events speed up (possibly, not sure about light travelling from external objects). At the event horizon objects will appear stationary for us, frozen in ...

1

You're right that there would be a disagreement over who signed the treaty first, but it would not be between the diplomats on the train; it would be between the people on the train and the people not on the train. The setup initially is that the two diplomats are sitting in the dining car with the curtains drawn, for security. Let's say the light that the ...

1

HyperLuminal asked: "Does that mean that electrons are infinitely stable?" Think about Dirac's model of an electron, which includes left and right handed contributions. Now add the (Nobel-worthy) Brout-Englert-Higgs idea, that the left-handed bit interacts with a condensate of weak hypercharge, while the right-handed bit does not. This suggests a ...

0

Special relativity itself makes it clear that absolutes cannot be detected, such as being at absolute rest in space, or the inability to detect absolute motion. This therefore prevents one from having an absolute understanding of special relativity, since that which special relativity reveals does not extend to the point of absolutes. Thus the absolute ...

0

Take a look at this pendulum periodicity calculator: http://hyperphysics.phy-astr.gsu.edu/hbase/pend.html. You can compare the period of each swing of the pendulum under different conditions of gravitational acceleration (little g in your formula). Notice that as gravity grows stronger (as gravitational acceleration becomes greater), the period of the ...

1

No, the relationship between the period of a pendulum and $g$ is simple Newtonian mechanics and unrelated to special or general relativity. This is discussed in the answers to Time period related to acceleration due to gravity (though I hesitate to link this as that question was not well received). Time dilation was actually known before Einstein formulated ...

4

Yes, there's a very famous example: muons produced in the upper atmosphere can be detected on the surface of the Earth. Moving at nearly the speed of light, it takes them over 300 microseconds to get down to the Earth's surface, but the average muon decays after 2.2 microseconds. If it were not for time dilation, only a few in every $10^{60}$ muons (so, ...

0

The pendulum motion is caused by a restoring force whose whose tangential component is opposite to displacement in direction. The tension from the string, if any, would always be perpendicular to the path. When there is no such force to provide the restoring force, the type of oscillation you mentioned would not happen. BTW, a kind reminder- Mathematics is ...

0

In that place, where g=0. T goes to infity. What it means?, just that the pendulum will not move. Just that. The time will run normally in that place and in the earth.

2

Let me clear up a few misconceptions. The edge of our observable universe would contain information from the beginning of the universe, since it is a particle horizon. However, the edge of the observable universe is not currently visible to us. What we can currently see only goes as far back as the recombination era, when electrons first joined with nuclei ...

-3

the time period in a SHM is related to the force causing the motion, the force which is proportional to the negative o the displacement. In the case of gravitational force, one simple example is that of the simple pendulum.T=2πLg−−√

34

The statement is true for decays, where lifetimes can be measured. It is not true for interactions though. A suicidal electron meeting a positron has a good probability to disappear, together with the positron, into two gamma rays, at low energies. Electron-positron annihilation It is intriguing that this is not true for neutrinos. If an electron ...

12

This is not exactly true. It is believed that net charge is conserved, but there is a weak process called electron capture, where an electron is captured by a nucleus, (usually from an inner "orbital" so there is a spectroscopic signature), a neutrino is emitted and a proton changes to a neutron. So therefore your textbook is wrong!

181

Imagine you are an electron. You have decided you have lived long enough, and wish to decay. What are your options, here? Gell-Mann said that in particle physics, "whatever is not forbidden is mandatory," so if we can identify something you can decay to, you should do that. We'll go to your own rest frame--any decay you can do has to occur in all reference ...

3

The practice of dividing the degree used to measure angle into sixty minutes of arc, and that into sixty seconds of arc is over 2000 years old. The corresponding practice of dividing the hour used to measure time into sixty minutes, and that into sixty seconds, is over 1000 years old. Why sixty? That's over 5000 years old. The Sumerians and Babylonians used ...

2

It's historical. The second was originally defined so that $60\cdot 60\cdot 24\,\rm s$ added up to a solar day. But that's a little hairy to measure, because the length of the day varies through the year. The sunrise-to-sunrise time varies from winter to summer. The noon-to-noon time interval, which would be operationally defined as the interval between ...

0

We need to first ask ourselves what is Space? What is Time? Then we can begin to answer your question after we define what these two are and the relationship between them. According to Geometrical Mathematics and based on Numerical Vector Space is nothing more then an empty construct and has no Dimensions until you give it a coordinate. We can define space ...

1

I feel like it is correct to call gravity a force. As you know, there are several models for how the universe works. The Newtonian model. The relativistic model. The quantum-mechanical model. Within certain different boundaries of scale, these each work very well at predicting things that will happen. However the language or terminology of each ...

Top 50 recent answers are included