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why do gravitational waves travel at the speed of light

why do gravitational waves travel at the speed of light插图

Two degrees of polarization
According to the Einstein’s general relativity,gravitational waves havetwo degrees of polarizationand,as a result,they travel at the speed of light.

Why do Gravitational waves travel faster than electromagnetic waves?

“So the fact that the speed of gravitational waves is equal to the speed of electromagnetic waves is simply because they both travel at the speed of information,” Creighton says. There’s an easy way to picture this, too.

Does gravity travel at the speed of light?

But it was also the first-ever direct confirmation that gravity travels at the speed of light. We all know light obeys a speed limit — roughly 186,000 miles per second. Nothing travels faster.

What is a gravitational wave and how did it hit Earth?

The collision was so extreme that it caused a wrinkle in space-time — a gravitational wave. That gravitational wave and the light from the stellar explosion traveled together across the cosmos. They arrived at Earth simultaneously at 6:41 a.m. Eastern on August 17. The event prompted worldwide headlines as the dawn of “multimessenger astronomy.”

How does the speed of light relate to quantum physics?

Moving electric charges that experience a changing external electromagnetic field will emit radiation, and that radiation both carries energy away and itself moves at a specific propagation speed: the speed of light. This is a classical effect, which can be derived with no references to quantum physics at all.

Why do we see redshifting waves?

Different observers would see gravitational waves redshifting and blueshifting due to all the effects — such as source/observer motion, gravitational redshift/blueshift, and the expansion of the Universe — that electromagnetic waves also experience.

What type of radiation is there in the context of general relativity?

Within the context of General Relativity, there’s a new type of radiation that arises: gravitational waves. Yet, despite having nothing to do with light, these gravitational waves must travel at the speed of light.

Why does light have 1.7 second delay?

The 1.7 second delay is very likely explained by the fact that gravitational waves pass through matter unperturbed, while light interacts electromagnetically, potentially slowing it down as it passes through the medium of space by just the smallest amount.

What are the two main theories of the universe?

There are two fundamental classes of theories required to describe the entirety of the Universe. On the one hand, there’s quantum field theory , which describes electromagnetism and the nuclear forces , and accounts for all the particles in the Universe and the quantum interactions that govern them . On the other hand, there’s General Relativity, which explains the relationship between matter/energy and space/time, and describes what we experience as gravitation. Within the context of General Relativity, there’s a new type of radiation that arises: gravitational waves. Yet, despite having nothing to do with light, these gravitational waves must travel at the speed of light. Why is that? Roger Reynolds wants to know, asking:

How does gravity affect general relativity?

But in General Relativity, these two extra pieces are at play: each object’s velocity affects how it experiences gravity, and so do the changes that occur in gravitational fields.

Why is gravity so revolutionary?

The reason it’s revolutionary is for this simple fact: if gravity simply attracted the planets to the Sun’s prior location at the speed of light, the planets’ predicted locations would mismatch severely with where they actually were observed to be.

How fast is gravity?

Through these observations alone, scientists determined that the speed of gravity was between 2.55 × 10 8 m/s and 3.81 × 10 8 m/s, completely consistent with Einstein’s predictions of 299,792,458 m/s.

Why is the speed of gravitational waves equal to the speed of electromagnetic waves?

“So the fact that the speed of gravitational waves is equal to the speed of electromagnetic waves is simply because they both travel at the speed of information ,” Creighton says.

What theory does Einstein use to explain the gravitational wave?

As with so much in physics, it has to do with Einstein’s theory of general relativity. Two neutron stars collide; the resulting gravitational wave spread at the speed of light. (Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonne) The dead cores of two stars collided 130 million years ago in a galaxy somewhat far away.

How long ago did the dead cores of two stars collide?

The dead cores of two stars collided 130 million years ago in a galaxy somewhat far away. The collision was so extreme that it caused a wrinkle in space-time — a gravitational wave. That gravitational wave and the light from the stellar explosion traveled together across the cosmos.

Which theory predicted gravitational waves?

That question requires a quick dive into Albert Einstein’s general relativity, or theory of gravity — the same theory that predicted gravitational waves a century ago. Einstein overthrew Isaac Newton’s idea of “absolute time.”.

Is time relative or finite?

But then Einstein showed that time is relative. It changes with speed and in the presence of gravity. One of the ramifications of that is that you can’t have simultaneous actions at a distance. So information of any kind has a finite speed, whether it’s a photon — the light-carrying particle — or a graviton, which carries the force of gravity.

Why is it wrong to take relativity into account?

This is because when you transform a field, you get velocity-dependent forces. This is true both in electromagnetism and in GR.

What happens when a charged particle is moving at a constant velocity?

If a charged particle is moving at a constant velocity, it exerts a force that points toward its present position, not its retarded position, even though electromagnetic interactions certainly move at the speed of light. Here, as in general relativity, subtleties in the nature of the interaction "conspire" to disguise the effect of propagation delay. It should be emphasized that in both electromagnetism and general relativity, this effect is not put in ad hoc but comes out of the equations. Also, the cancellation is nearly exact only for constant velocities. If a charged particle or a gravitating mass suddenly accelerates, the change in the electric or gravitational field propagates outward at the speed of light.

Why is accelerated motion extrapolated?

With gravity, accelerated motion is extrapolated to very high precision, due to effects that can be thought of like gravito-magnetism. And ideal point bodies in orbit (or other gravitational interaction) would radiate only a miniscule amount of gravitational waves due to being accelerated.

What happens when an electric field moves?

You can understand this with electric fields: a moving electric charge in the field will experience a magnetic force sideways, and the result is attraction to the linear extrapolated position of the other charged particle.

What is the meaning of "back up"?

Making statements based on opinion; back them up with references or personal experience.

Is GR a scalar potential?

It is not true that GR describes changes in a scalar gravitational potential as propagating with no delay. It’s actually not even true that GR describes gravity as arising from a scalar gravitational potential. Most spacetimes in GR cannot be described by a scalar gravitational potential. The thing that Newtonian gravity describes as a scalar gravitational potential is actually analogous to the metric in GR, and the metric is a tensor, not a scalar.

What does it mean when a field moves inertially?

What is probably causing people to tell you these incorrect things is a misunderstanding of a somewhat more subtle fact about fields, which is that when a source moves inertially, its field points toward it, not toward where it used to be. This applies to other fields, such as the electric field. This does not mean that a disturbance propagates instantaneously when the source does not move inertially.

What equations did Maxwell use to determine the speed of light?

Nonsense. Maxwell derived his electromagnetic equations, with ? 0 and μ 0, and those quantities were known. The fact that his equations led to the speed of electromagnetic waves to be, in terms of ? 0 and μ 0, equal to the approximately then known speed of light is a big part of what led Maxwell to conclude that light is electromagnetic.

What happens when two neutron stars come closer?

When two self rotating neutron stars come closer the magnetic fields of the stars are disturbed and energy waves are released from the magnetic fields. These waves are gravitational waves. Since they are from magnetic fields, they are of electromagnetic wave type. So, speed of gravitational waves is equal to the speed of electromagnetic waves in vacuum.

How did Einstein get the gravitational wave?

Finally, it’s gravitational wave speed also because Einstein got GR (general relativity) through a (mind blowing) generalization of special relativity to an arbitrary frame of reference , with gravitation equivalent to acceleration (equivalence principle). SR (special relativity) included c, the speed of light, as the maximum speed possible, achieved by zero mass particles. GR had to reduce to SR in a local inertial frame, so it also had to include the same c. GR waves reduce to a Lorentzian wave equation with c, in the weak field limit. Also in a local inertial frame.

What is the difference between gravitational waves and light?

Gravitational waves, on the other hand, interact with this very diffuse gas much less, so their speed is in practice closer still to c s (if someone would care to place a number on this so as to improve this answer, please do).

How long does it take for a gamma ray burst to occur?

This is one among the articles which refer to a time delay of 1.7 seconds in observing a gamma ray burst following an observation for gravitational waves. That is, gravitational waves were observed first and then light rays (gamma-ray-burst) were observed after 1.7 seconds from a collision of two neutron stars which are about some billion light years distance from our earth. Even if we begin with the assumption that incidents for both observations happened simultaneously at stars, then we find that speed of gravitational waves should be greater than the speed of light rays of gamma-ray-burst. Since no energy wave in “vacuum” can exceed speed of light in “vacuum”, then we can conclude that the gravitational waves were released first and the light waves were released second. Elementary numerical calculations also show that the difference 1.7 seconds in reaching earth from a billion light years distance place does not make any significant difference between speed of gravitational waves and speed of light rays. So, the speed of gravitational waves should be equal to the speed of light rays, and the event of occurrence for gravitational waves happened first and the event of occurrence of light rays happened second (at the place of stars). So, no deep physics and no deep mathematics are involved in the conclusion that the speed of gravitational waves is equal to the speed of light rays in vacuum. I like to add some more things without giving a reference for basic principles (to avoid “self-promotion”).

How many reputations do you need to answer a highly active question?

Highly active question. Earn 10 reputation (not counting the association bonus) in order to answer this question. The reputation requirement helps protect this question from spam and non-answer activity.

Does spacetime cause gravity to propigate at the same speed?

With nothing to cause it to go slower, changes to electric and magnetic fields will occur at that speed. No coincidence that changes to spacetime (causing gravity) propigate at the same speed.