If the universe expands does spacetime,dark energy,dark matter,gravity expands also ?

Do forces,energy/matter expand with the universe also ?

When we say that the universe is expanding ,what is actually expanding ?


1 Answer 1


The universe is expanding, and the expansion accelerates.

The expansion of the universe is the increase of the distance between two distant parts of the universe with time.[1] It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand "into" anything and does not require space to exist "outside" it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale.


What is really expanding is space itself.

Now on the large scale the expansion of the universe is uniform.

Though, there are regions, like inside galaxies, where gravity dominates, and space is not expanding. It is because gravity binds matter together strong enough so that there is no space expansion on these smaller scales.

In the regions, where dark energy dominates, like in the intergalactic voids of space, space itself is expanding.

Now you are asking about dark energy.

Physicists have postulated the existence of dark energy, appearing as a cosmological constant in the simplest gravitational models, as a way to explain the acceleration. According to the simplest extrapolation of the currently-favored cosmological model, the Lambda-CDM model, this acceleration becomes more dominant into the future. In June 2016, NASA and ESA scientists reported that the universe was found to be expanding 5% to 9% faster than thought earlier, based on studies using the Hubble Space Telescope.[2]


Now you are asking whether dark matter is expanding. Inside galaxies (matter or dark matter) gravity dominates. Thus, space is not expanding, because gravity binds matter (or dark matter) together strong and dominates over dark energy inside the galaxies.

You are asking whether forces are expanding. Now this can be interpreted as asking how the scale of forces (the distance they interact at) changes with space expansion. The answer is no. Forces, EM, gravity, strong, weak, and their characteristics (the distance they act on) does not change.

You are asking whether energy expands. The only case when this question could be interpreted, is if energy would expand (in scale) if we would consider a photon traveling through expanding space, thus the photon's wavelength gets stretched, it loses energy.

  • $\begingroup$ We have no knowledge of what is outside the universe, if anything, and we should not pretend that we do. Some people suggest there are other universes alongside ours, but that is pure speculation and untestable, as is any other statement abut what lies outside the universe. $\endgroup$ Jul 24, 2019 at 16:14
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    $\begingroup$ @MichaelWalsby I agree. Where do I mention anything about outside the universe? $\endgroup$ Jul 24, 2019 at 16:15
  • $\begingroup$ So what you are saying is that the Universe is space and not the system that has "everything" inside it ? $\endgroup$
    – jim101
    Jul 24, 2019 at 17:47
  • $\begingroup$ @jim101 "The Universe is all of space and time[a] and their contents,[10] including planets, stars, galaxies, and all other forms of matter and energy. While the spatial size of the entire Universe is unknown,[3] it is possible to measure the size of the observable universe, which is currently estimated to be 93 billion light years in diameter." en.wikipedia.org/wiki/Universe $\endgroup$ Jul 25, 2019 at 10:57

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