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our Universe is composed of stars and planets, exotic objects like magnetars and pulsars, dust and radiation, and all importantly, spacetime.
the fabric of the Universe.
the stuff that creates the effects of gravity, and shapes the trajectory of light.
the fabric of the Universe.
the stuff that creates the effects of gravity, and shapes the trajectory of light.
massive celestial bodies, like stars and galaxies, warp spacetime with their gargantuan mass.
if you imagine a bowling ball resting on a trampoline, the ball is the massive object (star) and the trampoline is spacetime.
if you imagine a bowling ball resting on a trampoline, the ball is the massive object (star) and the trampoline is spacetime.
the bowling ball indents the trampoline, & anything thrown onto the fabric (say, a golf ball) whirls around, orbiting towards the bowling ball.
this is the same effect of gravity in our Universe-- for ex. Earth orbits the Sun because of the Sun's large mass indenting spacetime.
this is the same effect of gravity in our Universe-- for ex. Earth orbits the Sun because of the Sun's large mass indenting spacetime.
spacetime doesn't just shape the effects of gravity.
it also shapes how light travels in the Universe.
it also shapes how light travels in the Universe.
when we look up at the stars, we’re looking back in time.
light travels at a constant speed. that means that when we look at objects in space—for example, a galaxy 1 million light years away, we are seeing it *as it was* 1 million years ago.
we’re cosmic time travelers.
light travels at a constant speed. that means that when we look at objects in space—for example, a galaxy 1 million light years away, we are seeing it *as it was* 1 million years ago.
we’re cosmic time travelers.
light sticks to the fabric of spacetime.
when light travels around a massive object, it travels along the warped path created by spacetime, bending around the massive object & creating beautiful effects like halos and rings.
[below is an Einstein Ring, by ESA/Hubble & NASA]
![light sticks to the fabric of spacetime. when light travels around a massive object, it travels along the warped path created by spacetime, bending around the massive object & creating beautiful effects like halos and rings.[below is an Einstein Ring, by ESA/Hubble & NASA]](https://pbs.twimg.com/media/EoK51UlVEAMrUYx.jpg "light sticks to the fabric of spacetime. when light travels around a massive object, it travels along the warped path created by spacetime, bending around the massive object & creating beautiful effects like halos and rings.[below is an Einstein Ring, by ESA/Hubble & NASA]")
when light travels around a massive object, it travels along the warped path created by spacetime, bending around the massive object & creating beautiful effects like halos and rings.
[below is an Einstein Ring, by ESA/Hubble & NASA]
but light haloes aren't the only spacetime effects on light in our Universe.
in 1929, we discovered that our Universe is not static but is, in fact, expanding.
and in 1998 we discovered something even more incredible: our Universe is not just expanding, it's accelerating.
in 1929, we discovered that our Universe is not static but is, in fact, expanding.
and in 1998 we discovered something even more incredible: our Universe is not just expanding, it's accelerating.
since the Universe is expanding, so is the fabric of spacetime within it.
and this means that the light 'stuck to' the fabric of spacetime is being stretched too.
and this means that the light 'stuck to' the fabric of spacetime is being stretched too.
light takes time to travel over distances.
so when we look out at distant galaxies, we are seeing them *as they were* when the light left their surfaces.
so when we look out at distant galaxies, we are seeing them *as they were* when the light left their surfaces.
but this light doesn't just arrive late, providing us a picture of the object as though we were looking back in time.
the light's *wavelength* is also different than it was when it left the original object, thanks to the expansion of the Universe.
the light's *wavelength* is also different than it was when it left the original object, thanks to the expansion of the Universe.
because spacetime expands with time, SO IS LIGHT STICKING TO IT!
light is literally being stretched alongside the spacetime it travels upon.
we see distant light *redshifted*, meaning it's stretched into the redder regions of the EM spectrum.
[gif by the brilliant @aibhleog]
light is literally being stretched alongside the spacetime it travels upon.
we see distant light *redshifted*, meaning it's stretched into the redder regions of the EM spectrum.
[gif by the brilliant @aibhleog]
this is why so many telescopes that look at far-distant phenomena in our Universe are in the infrared-- they are looking for light that has had its wavelength stretched, lengthening it and placing it firmly in the infrared portion of the electromagnetic spectrum.
