Why can't we measure Earth's absolute speed in space?

[hafiz ns]

we cannot find Earth speed..,.,.,.,,.
to find speed of an object we want a stable surface.
lets go through an example:-
if a train in moving with a speed of 100 km/hr and a car is in top of the train moving with a speed of 50 km/hr (in same direction). then the speed of car is 150 km/hr.

In this situation let's take the car as Earth and the train as solar system.
the Earth is moving with a speed of 1670 km/hr and the solar system is moving with a speed of 828000 km/hr . the solar system is in galaxy moving with a speed of 130 km/sec.
hence to find the speed of Earth we have to add these all matters:-

just like:-
1670+828000+and the speed of galaxy = speed of earth
till this time we don't know that the galaxy is inside any stuff. if yes we don't know the speed of that stuff
so we can't find the speed of earth
iam confused please replay fast.,.,.,

 

[Orodruin]

A velocity of its own does not mean anything so you cannot say that the velocity of an object is a particular number. You can only define relative velocities, ie, how fast things move relative to each other. This is true for all objects.

 

[hafiz ns]

but does it have any possibility ?

 

[Orodruin]

No, because as I just told you, the question has no meaning.

 

[marcus]

...
to find speed of an object we want a stable surface.
... we don't know that the galaxy is inside any stuff.
if yes we don't know the speed of that stuff
so we can't find the speed of Earth

To expand on what Orodruin said: for specific applications we can give the speed of the solar system (for example) a useful meaning, by CHOOSING a background or frame of reference.

One of the most useful reference frames is that of the cosmic microwave background CMB. We are surrounded by a kind of "soup" of ancient light---the most ancient light we can detect.

It is essentially all the same temperature, as long as we adjust for the Earth and solar system moving thru it. We are moving at 370 km/second in a certain direction thru this light. The doppler effect of our motion causes there to be a "hot spot" in the sky in the direction we are going.

Because we are running into the light and that makes us see the light in that direction with a little more energy---about one tenth of one percent warmer.

If we cancel out the doppler effect of our own motion relative to CMB, that is remove that hot spot (and the doppler cold spot in the opposite direction) from the data, then the CMB appears essentially the same temperature in all directions. With just some tiny fluctuations.

The CMB is the leftover glow from the ancient matter of the universe---the original hot gas as it was at the time when it had become just cool enough to be transparent, so that its light could go free without being scattered and could come down to us. (with its wavelengths stretched out by expansion but otherwise mostly unchanged) We SEE the ancient matter by this ancient CMB light and we see our motion relative to this ancient matter by the doppler effect of moving 370 km/s relative to it.

If you want to talk about motion and speed of motion you have to first give it a meaning by saying what the motion is relative to.

 

[Neon]

to find speed of an object we want a stable surface.
lets go through an example:-
if a train in moving with a speed of 100 km/hr and a car is in top of the train moving with a speed of 50 km/hr (in same direction). then the speed of car is 150 km/hr.

In this situation let's take the car as Earth and the train as solar system.
the Earth is moving with a speed of 1670 km/hr and the solar system is moving with a speed of 828000 km/hr . the solar system is in galaxy moving with a speed of 130 km/sec.

Gotta correct misconceptions.

Start from one minute or just watch the whole thing for more stuff.
Though small but we must get our facts correct.