Understanding the Expanding Universe and Its Impact on Earth's Distant Future

In summary, the universe is expanding, causing large portions of about 300 million light-years to get away from each other. However, in smaller scales such as within galaxies and solar systems, gravity is strong enough to hold everything together. Without the sun, it is likely that all organisms on Earth would die. Scientists have estimated that the sun will turn into a red giant in about 7.10^9 years, destroying the Earth. There is also a possibility of the universe reaching a state of heat death in the far future. Some researchers believe that the dark energy driving the current accelerated expansion of the universe may have a varying energy density, which could potentially lead to a big rip in the future. However, this is still a hypothetical fate
  • #1
kenny1999
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4
Universe is expanding which means the Earth is getting away from the sun. Without the sun, it is probably that all organisms on the Earth would die. Is there any calculation or estimation from scientists that how many years before the Earth is too far away from the sun so that we will all die
 
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  • #2
kenny1999 said:
Universe is expanding which means the Earth is getting away from the sun.

No. It does not mean that. It means that huge portions of about 300 million light-years (more or less) are getting away from each other.

In smaller scales (small group of galaxies, inside a galaxy, in our solar system) things are not getting away from each other (on average).

Without the sun, it is probably that all organisms on the Earth would die. Is there any calculation or estimation from scientists that how many years before the Earth is too far away from the sun so that we will all die

You'd better worry about the Sun turning to a red giant in about 7.10^9 years and destroying the Earth.
 
  • #3
kenny1999 said:
Universe is expanding which means the Earth is getting away from the sun.

Partially true. The universe is indeed expanding. However, the expansion of space does not take place within galaxies and solar systems because gravity is strong enough at these distances to hold everything together. It is only when distances between objects gets REALLY big and gravity gets very weak that expansion starts to take over. So, in effect, expansion causes galaxy clusters to recede from each other, but nothing within a galaxy clusters recedes from anything else within the same cluster.
 
  • #4
Just for fun, let's try doing the math. There are 9.46E15 meters in a light year and 3.26 million light years in a megaparsec. That makes for a total of about 3E22 meters per megaparsec. The expansion rate of the universe is about 70,000 m/sec/mpc which is roughly 1 m/sec for every 4.4E17 meters. Earth's distance from the sun is about 150 billion meters. That means [ignoring gravity] the Earth and sun would currently be receding at a rate of 3.4E-07 meters per second, or about 10.7 meters per year. This same reasoning yields a recession value of the moon from Earth [d=384 million meters] of 8.73E-10 meters per second, or about 2.75 centimeters a year. We have measured the actual recession speed of the moon [3.8 cm] and it is explained by tidal friction. The Lunar Laser Ranging experiment should have detected an anomalous extra 2.75 cm of recession per year if expansion played a role.
 
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  • #5
mattt said:
No. It does not mean that. It means that huge portions of about 300 million light-years (more or less) are getting away from each other.

In smaller scales (small group of galaxies, inside a galaxy, in our solar system) things are not getting away from each other (on average).



You'd better worry about the Sun turning to a red giant in about 7.10^9 years and destroying the Earth.

The world should have already used up all the energy and resources and killed itself well before the sun destroying the Earth. Do you agree
 
  • #6
Drakkith said:
Partially true. The universe is indeed expanding. However, the expansion of space does not take place within galaxies and solar systems because gravity is strong enough at these distances to hold everything together. It is only when distances between objects gets REALLY big and gravity gets very weak that expansion starts to take over. So, in effect, expansion causes galaxy clusters to recede from each other, but nothing within a galaxy clusters recedes from anything else within the same cluster.


Why big stuff would have weak gravity?

It contradicts according to F=GMm/r^2
 
  • #7
kenny1999 said:
Why big stuff would have weak gravity?

It contradicts according to F=GMm/r^2
Well, what does r stand for? What happens to F when r is large?
 
  • #8
kenny1999 said:
Why big stuff would have weak gravity?

They don't. But the distances between galaxy clusters is staggeringly large. Tens of millions of lightyears on average. This greatly reduces the gravitational attraction between.
 
  • #9
But in the far future, the accelerating expansion will overcome gravity, tear apart super clusters, then clusters, galaxies, solar systems, the whole shebang. Only photons will be left wondering about in an empty universe.
Is this not the interpretation by most, well, many, cosmologists? :frown:
 
  • #10
the big rip is invalidated, in order for the big rip to work the cosmological constant would have to gain energy density strong enough to overcome the strong force and gravity. However the cosmological constant has been shown to have a constant energy density. Instead we are heading for what is known as heat death.
http://en.wikipedia.org/wiki/Heat_death_of_the_universe
even then this fate is hypothetical
 
  • #11
Mordred said:
the big rip is invalidated, in order for the big rip to work the cosmological constant would have to gain energy density strong enough to overcome the strong force and gravity. However the cosmological constant has been shown to have a constant energy density. Instead we are heading for what is known as heat death.
http://en.wikipedia.org/wiki/Heat_death_of_the_universe
even then this fate is hypothetical
This is not right. We don't know that the dark energy driving the present-day accelerated expansion is actually constant. This is based on observational constraints on the equation of state parameter, w. While there are no statistically significant deviations from w = -1 (a cosmological constant), it is still perfectly likely that the equation of state is consistent with a varying energy density, even one leading to a big rip: http://arxiv.org/abs/1303.4353
 
  • #12
hrmm interesting hadn't seen that paper before thanks, has there been any further findings in regards to a varying cosmological constant in the last year that your aware of?
 
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  • #13
If I understand correctly some researches think we are in a "dark energy" phase of evolution of the Universe, considering that periods have existed in which relative importance, even existence, of determining factors have changed during succeeding epochs. Deductive reasoning often falls into the "if this, then that" category and that works but is not without limitations. If humans, like dragonflies, had lifespans of one day, it might be very difficult to imagine snow, let alone Winter, if you were born, say, during June.

That said, unless some major change occurs, and there is certainly enough time (and possibly, space) for such to occur, it is impossible or at least fruitless to speculate. "Smart Money" is on No Big Rip.
 
  • #14
I think Cooperstock, Faraoni, Vollick’s 1998 The influence of the cosmological expansion on local systems contains a good technical paper explaining why the metric expansion of space isn’t noticeable on solar system scale. In section 4-"Cosmological corrections to the two-body problem in the LIF", they calculate a fractional change in period of orbit of 2.8e-33/year, which (courtesy of Kepler’s 3rd law) give an increase in the radius (more correctly, semimajor axis) moon’s orbit of 2.8e-33^(2/3)*386e6 = 7.6e-14 m/y, on the order of 1/10^22th the observed rate and the rate calculated by post #4’s straightforward application of the current Hubble’s constant

I don’t feel technical explanation are very intuitively satisfying, though. While it’s accurate to state that the reason Expansion is so much smaller on interplanetary scales than given by the Hubble constant, such statements don’t feel detailed enough. So I find it intuitively appealing to take a simple 2-body, one big, one tiny, in a circular orbit, simulation and add a small constant outward radial acceleration to the tiny body. Coincidentally, I recently ran a simulation for a solar sail at various angles relative to the direction of the Sun, which in the 90deg case and a very low acceleration, is nearly identical. What happen in this case is that the body doesn’t transfer to a different orbit, but follows a forced, precessing elliptical orbit with periapsis matching the initial circular orbit.

While Expansion causes no detectible increase in radius or orbit, perhaps it causes a very small deviation in the General Relativity-predicted precession of the orbit that could be detected? Alas, my GR physics skills aren’t up to calculating it.
 

1. What is an expanding universe?

An expanding universe refers to the concept that the space between galaxies and other celestial bodies is constantly increasing, causing the universe to grow larger over time.

2. How do we know that the universe is expanding?

Scientists have observed the phenomenon of redshift, where light from distant galaxies appears to be shifted towards the red end of the spectrum. This indicates that those galaxies are moving away from us, providing evidence for an expanding universe.

3. What is causing the expansion of the universe?

The leading theory is that the expansion is driven by dark energy, a mysterious force that makes up about 70% of the universe's total energy. It counteracts the force of gravity and causes the universe to expand at an accelerating rate.

4. Will the expansion of the universe ever stop?

It is currently unknown if the expansion will continue indefinitely or eventually slow down and stop. It depends on the amount of dark energy in the universe and how it interacts with the other forces at play.

5. What does the expanding universe mean for the future of the universe?

If the expansion continues, it is possible that galaxies will eventually become too far apart to interact with each other, resulting in a "heat death" of the universe. However, this is just one possible outcome and there are many theories about the ultimate fate of the universe.

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