# Tag Info

## New answers tagged relativity

0

The notion of absolute time for all observers in all reference frames has been debunked by Einsteins theory if special relativity. Prior to that, scientists believed that there might be an ether that permeated all space, and from which a universal reference frame could be derived. However, when Michelson and Morley did their famous experiments attempting to ...

1

There isn't a such thing as "absolute time." Some events – they are called space-like events – can't even be agreed to happen in an "objective order." Only time-like events can be universally agreed to happen in a particular order, but there's no such thing as "universal time." For you, time will always tick per one second by second, and that will apply to ...

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Is there an absolute pace of time, no. Is your clock , in a region without gravity, (and at "rest" relative to other objects) "ticking" faster than your alarm clock on the Earth's surface, yes. But obviously you physically cannot escape the effect of gravity, no matter how far away the mass-energy sources are, so this will vary from observer to observer, ...

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You're quite correct that measuring time from the Big Bang does separate spacetime into a time bit and a space bit, but this isn't arbitrary. When we want to describe the universe around us we need to choose some coordinate system that we can use to record physical quantities. Whatever coordinate system we choose will have one coordinate that behaves like ...

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The speed of light wouldn't stop time but make it extremely slow. After u have traveled the distance light travels in a sec then you will pass 1 second in space time assuming you are still whole and have not turned into a photon which would break so many rules.

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The answer is an emphatic yes! We can find the actual rest mass of things on earth. How the earth is moving with respect to the sun, galaxy,etc., is irrelevant. By saying, "on earth," the frame of reference is specified (the earth), so whatever mass a thing has on earth, (as long as it is not moving with respect to the earth), is its actual rest mass! In ...

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My question is, are we really must say that the energy of the tide and the loss of the kinetic energy of the moon are equal? The answer is obviously "YES." It must be so. I would refer at this point these words; Nature is relentless and unchangeable, and it is indifferent as to whether its hidden reasons and actions are understandable to man or not.- ...

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When the object is an elementary particle or a charged ion we can use electromagnetic interactions to measure its rest mass, given the charge in an e/m experiment. One can get the charge with Milikan's oil drop experiment. Here is a setup for the lab.

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Earth moves around the Sun and the Sun moves around the galaxy and the galaxy moves with unknown speed and direction. We have speed so the mass of us all altered. The relativistic mass is altered, but this is a somewhat archaic term these days, and is said to be a measure of energy. Nowadays when we say mass without qualification, we tend to mean rest mass. ...

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The rest mass of an object, by definition is the total energy of an object as measured by an inertial observer who is at rest relative to the object. If the object is not moving uniformly, then you can measure its rest mass from a momentarily co-moving freefall frame. This rest mass is also the constant in Newton's law, i.e. the inertial mass as well. So ...

2

We do have a rough idea of the relative speed and direction of our galaxy, with respect to the other galaxies around us, the so called local group. In general relativity, which is our best theory of the universe to date, there is no such thing as absolute speed, as it depends on which frame of reference you use to measure things in. Our Earth and the ...

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How can you explain objects of unequal masses falling at the same rate using GR? up vote By explaining why light curves, then by using the wave nature of matter to explain why an electron falls down, and then explaining that an ensemble of electrons (and other particles) falls down at a rate that is irrespective of the number of particles in the ensemble. ...

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No: Photons were first created around 10 seconds after the Big Bang, when particles and anti-particles annihilated. For 380,000 years, the Universe was hot enough that all matter was ionized, and since on top of this the Universe was very dense in the beginning, the mean free path of photons — i.e. the average distance traveled by a photon before it ...

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A photon alone doesn't have memory and doesn't carry any clock. An assembly of photons, selected by many technics, might carry collective correlated informations, like the redshift , the statiscal polarization , gravitational lenses detections etc. The redshift is similar to a clock.

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If Galileo had dropped the Moon and a pebble from a very tall tower, the Moon would have fallen noticeably faster, relative to the Earth. This is true in Newtonian physics as well as GR, and it does come from the fact that the Earth falls toward the Moon too, and harder than it falls towards the pebble. The assumption that small objects do not gravitate is ...

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The strength of gravity is given by the space-time curvature caused by all the objects in the system, in this case both the earth and the falling object. The problem is that you are ignoring the fact that the space-time curvature caused by the earth is many, many times larger than that caused by the falling object. Hence, the total curvature is to all ...

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Your post has many details, but overall you were a little vague about the signature (++++, +++-, ++--, +---, ----) of the metric. In fact it only came up when you said the metric is close to $\eta$ when two points are close. And that could be interpreted ina way that isn't true. For any point there exists a coordinate system where the metric is very close ...

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Proper acceleration is acceleration away from following a geodesic. As such, it is $0$ if and only if the object in question is free falling. If there is any net non-gravitational force, then there is proper acceleration. Standing still on the Earth's surface is not free falling. The ground is preventing free fall, and proper acceleration is $g$. Note that ...

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I think you are mixing up two different concepts, which is muddying the waters. Firstly, relativity (both special and general) is a geometrical theory and the proper time for an observer has a precise definition as the length of a world line along which the observer travels (give or take a factor of $c$). This length is calculated using the metric. As ...

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Proper time of an observer is time as measured by the observer's own clocks. So it's obviously frame-independent because calculating proper time of a given observer requires to use his own frame of reference.

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