The universe travels 300,000 kilometers per second which’s 7.5 times around the Earth each second. The galaxies of the Milky Way contain 10 billion and one billion stars, respectively. But they’re tiny little galaxies that don’t amount to much. The first real galaxy of any size is the Andromeda Spiral, about two million light-years in the distance. It’s a galaxy that’s a little bigger than the Milky Way but the tip of the iceberg.
In the beginnings of cosmology, the light from stars spread out into the colors of the rainbow, which is a spectrum. A star’s spectrum reveals what the star’s made out of because every element has a fingerprint. A fingerprint of light and color that it absorbs and emits. For example, sodium has a fingerprint where it radiates an orange-yellow color.
Light from the edges of the 42 million light-years sphere began its journey to where the earth developed about 13.7 billion years ago. But during the trip, the intervening space multiplied itself 1090 times. The spherical shell from which the light began is about 46 billion light-years away.
A hundred million years after inflation, the first stars formed. They were massive giants formed in every region of space, including tiny spheres of the observable universe. Those formed on a little shell inside our expanding particle horizon are visible today.
Does the universe expand faster than the speed of light?
According to current scientific understanding, the universe’s expansion does not violate the speed of light limit. However, it’s important to clarify a few key points:
Expansion of Space: The universe expands, meaning the distances between galaxies increase over time. This expansion is driven by the overall geometry of space rather than objects moving through space. The space between galaxies is stretching rather than objects within the space.
Speed of Light Limit: According to the theory of relativity, nothing can travel through space faster than the speed of light in a vacuum, which is approximately 299,792 kilometers per second (or about 186,282 miles per second). This limit applies to the motion of objects through space, not to the expansion of space itself.
Expansion Rate: The Hubble constant parameter describes the universe’s expansion. The current best estimates of the Hubble constant suggest that the expansion rate is around 70 kilometers per second per megaparsec. This means that for every megaparsec (about 3.26 million light-years) of space, the galaxies in that region move away from each other at a rate of 70 kilometers per second.
Cosmic Horizon: Due to the expansion of space, there are universe regions beyond our observable horizon. These regions are moving away from us faster than the speed of light, but this does not violate the speed of light limit. It is essential to understand that the speed of light does not constrain the expansion of space itself.
Some galaxies should move away faster than light if space is big enough. But how is that possible? Doesn’t light travel at the universal speed limit? Hubble’s law says the further away an object is, the faster it recurs without limitation. So there are always objects far enough away to be reducing faster than the speed of light objects.
The farther away from the source, the longer the time. The cosmic microwave background, or CMB, has taken 13.8 billion years to get here. The point is that light takes time to get places, sometimes a long time. So, the speed of light isn’t a speed limit for all speeds. Plenty of things go faster, and the speed of light isn’t a universal speed limit.
It’s the speed limit of causality, cause, and effect. How can you get the distance between things using the Pythagorean theorem? A squared plus B squared equals C squared? If you make time one of those dimensions, it still works. This equation governs the order of cause and effect. It represents how quickly parts of space can communicate across time. The speed of light isn’t really about light. It’s about causality, cause, and effect.
If one event causes another, everyone agrees on the order of those events. The cause must come before the effect. The laser on the Moon makes it excellent for the dot to move faster than light. The events on either side of the Moon aren’t causally connected, so there’s no speed limit. The cause is back on Earth with the laser. The photons from the laser still can’t get to the Moon faster than light. So there’s a delay between moving the laser and the dot moving on the Moon.
As long as causality is maintained, things can go as fast as they want. That’s a rule that applies even in cosmology. It’s magnificent for distant galaxies to go faster than light as long as they’re not causing anything faster than light.
The faster objects go, the more and more kinetic energy needs to keep going faster. It needs infinite energy to accelerate to the speed of light. So how can distant galaxies or the universe break that rule? That simple rule is only a special case, so we call the model Special Relativity. It is General Relativity, and it’s necessary for cosmology. In fact, in general, relativity, what it looks like, depends on the circumstances, and it can get pretty complicated sometimes. It looks like a rotating black hole.
On cosmological scales, the universe is extremely uniform and simple. It’s called the scale factor, which represents the scale of space. As space expands, the scale factor gets bigger. That’s why distant galaxies or the universe can move away/expand faster than light.
They’re carried along as space expands. The universe’s distance is expanding away at precisely the speed light is called: The Hubble Horizon. It’s 14.5 billion light-years away, about 14.4 billion farther than human brains could ever hope to comprehend.
There are two more horizons beyond it:
- One is our vision limit of the present.
- The other is our vision limit of the past.
That last one is three times farther than the Hubble horizon.
The time that Earth does not measure is called “cosmic time.” It’s the time measured by someone who isn’t moving relative to the source of the CMB. The CMB is the inside surface of a sphere. In its raw form, it’s red-shifted in one direction and blue-shifted in the other. That tells that Earth is moving relative to whatever stuff emits that light, which isn’t the most convenient point of view for cosmology.
The proper distance between galaxies is increasing. This is the distance we see when we look out into the universe. But the comoving distance is much more convenient in cosmology. It’s called “comoving” because it co-moves with expanding space. As space expands, the grid goes with it. Distant galaxies remain roughly the same comoving distance from each other as time passes.
This coordinate doesn’t change with the expansion. The scale factor does. That gives people the impression galaxies can’t move in comoving coordinates, and they can. As two galactic clusters expand away from each other with the grid, the galaxies inside those clusters can also move around locally a little bit. Both of these can change. A change in the scale factor represents the expansion, and a change in the comoving coordinate represents actual local motion.
That’s the loophole in physics that distant galaxies exploit to go faster than light. Since both can change, there are two velocities: A recession velocity because it measures things receding from us, and a peculiar velocity.
- The recession velocity is bigger than the speed of light.
- The peculiar velocity is the one that must be slower.
Remember, this all started with causality, with the order of cause and effect. The speed of light isn’t the upper limit on how fast things can move. It’s the upper limit on how fast two points in space can communicate with each other. Only the peculiar velocity lets parts of space communicate, so only that velocity has the speed of light limit. The recession velocity is an illusion created by the expansion of space.
Expanding universe law: A galaxy’s velocity is directly proportional to its distance.
v = Hr; Where, v = recessional velocity, H = Hubble constant, r = distance
Hubble’s law states a correlation between the distance to a galaxy and its recessional velocity determined by the redshift.
The rate of expansion isn’t even measured as a speed. It’s measured as speed a distance. It’s about 70 kilometers per second per megaparsec, also called the Hubble parameter. That means galaxies are moving away at 70 kilometers per second for every megaparsec they are distant.
- 1 megaparsec = 3.3 million light-years or 3 billion trillion kilometers from Earth.
- The universe is expanding 73.5 ±1.4 km/sec/Mpc.
The difference between the two speeds explains the difference between two types of redshift: Doppler redshift and Cosmological redshift. These two different velocities result in two different redshifts. The second one gives the Doppler redshift because it’s an actual velocity.
The first one gives cosmological redshift, and the expansion of space causes the redshift. It’s not a velocity, so it can’t be the same as Doppler. Doppler redshift maxes out at the speed of light. Cosmological redshift does not.
How do we know the universe is expanding faster than light?
To understand expanding universe and redshift, we must understand the Doppler effect. The Doppler effect essentially means that when a wave travels away from an observer, the wavelength of the wave increases. In terms of wavelength, the distance between two waves: when the status matrix is an observer, the wavelength decreases, and moving away for an observer, the wavelength increases. There’s a relationship between frequency and wavelength. So the wave speed is equal to the wavelength times the frequency.
The frequency and the wavelength are inversely proportional. As the wavelength increases, the frequency decreases. So when the wave moves toward an observer, the wavelength will be low and a high frequency. Light is part of the electromagnetic spectrum. So in order, the visible light is red, orange, yellow, green, blue, indigo, and violet.
Edwin Hubble identified that the light coming from distant galaxies was red-shifted. So that meant the light had shifted toward this end of the spectrum in that direction. The wavelength of the light coming from those distant galaxies had a longer wavelength.
It means that the light source is moving away from the observer. So Edwin Hubble could say that redshift means light from those distant galaxies is moving away. This is evidence that the universe is expanding.
The light from these primitive giants has been traveling for over 13 billion years. The shell of space they formed is now over 36 billion light-years away. So light from the microwave background was emitted from a distance of 41 million light-years away. That distance is now 46 billion light-years.
Light from the earliest stars was emitted from a distance of 1.5 billion light-years, which has grown to 36 billion light-years. Due to the faster-than-light expansion of space in those early years. For billions of years before, the slowing expansion allowed it to start moving toward us.
Overbye, Dennis (20 February 2017). “Cosmos Controversy: The Universe Is Expanding, but How Fast?”. The New York Times. Retrieved 21 February 2017.
Radford, Tim (3 June 2016). “Universe is expanding up to 9% faster than we thought, say scientists”. The Guardian. Retrieved 3 June 2016.
Slipher, V. M. (1913). “The Radial Velocity of the Andromeda Nebula.” Lowell Observatory Bulletin. 1: 56–57.
“Vesto Slipher – American astronomer.”
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