# What is Expansion rate: Definition and 26 Discussions

Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster weakening the intermolecular forces between them, therefore expanding the substance.

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1. ### I Relationship between geometry and expansion rate

As I understand it, the flatness problem of Bob Dicke, says a flat universe in unstable and so has to be set very precisely in the early universe to give us the flat universe we see today. Is this the same problem as saying the expansion rate had to be finely tuned and if so how are the two...
2. ### B Expansion Rate of the Universe

I hope that I am conveying what I see in my head clearly. I guess that I am visually imagining the 3 spatial dimensions projected on the 2d surface of a sphere and as that sphere expands that the increased distance between 2 points would happen what seems like at an accelerating rate because of...
3. ### B Universe expansion rate in m/s^2 ?

Summary: Is it possible to tell the current average universe expansion rate i.e. acceleration of expansion in m/s^2 ? Is it possible to tell the current average universe expansion rate i.e. acceleration of expansion in m/s^2 ? If i say in relation to earth, does this make it easier to answer...
4. ### I Does the newly measured expansion rate change the odds for Big Rip?

Is the likelihood (or unlikelihood) of a Big Rip changed by the new findings of faster universe expansion (https://www.sciencedaily.com/releases/2019/04/190425104128.htm). In https://www.physicsforums.com/threads/will-the-big-rip-basically-be-the-big-bang-for-the-next-universe.971039/, phinds...
5. ### B Measuring the Universe's expansion rate

From our perspective the Universe is expanding faster the further away things get, correct? Given that we are measuring further and further back in time my question is this. If you were at the furthest known point in the Universe looking back at our galaxy and attempting to measure the expansion...
6. ### I Gravitational Waves vs Universe Expansion Rate

Is there any relationship between the Speed of gravitational waves and the Universe's "local" expansion rate? Speed of gravitational waves is supposed to be equal to the speed of light. Gravitational waves don't travel faster than light. But we can observe far galaxies moving away from us with...
7. T

### I Expansion Rate of Cosmic Bubbles

I’ve understood that within the theory of Eternal Inflation the Bubble Universes that form from a drop of “vacuum” energy expand at the Speed of Light. My question is: Why would expansion be at the speed of light and not at a speed proportional to the level of vacuum energy still present in...
8. ### B Is the Expansion Rate Truly Accelerating?

I'm studying about accelerating expansion rate. I am reading that the rate of expansion is accelerating. Now the farther objects are from us the faster they are moving away from us due to expansion. Farther and farther, faster and faster. But that would occur even if the expansion rate is...
9. ### Speed and / or expansion rate of the Universe?

Is it true that the universe itself expands faster than c = 3 × 10^8 m/s at some places / areas / points. I have heard it but wasn't able to confirm. Because outside of the the universe, there ain't anything as far as we understand and hence the universe should not have to follow any law as...
10. ### What if expansion rate of a universe is the speed of light?

What If we accept starting point of the big bang as the central point and what If the equatorial expansion rate of a spinning universe was the speed of light, how would it impact universe? ( In this question, you may think yourself as an observer from out of universe. I try to mean with "the...
11. ### Dark energy and type 1a supernovae?

I am trying to wrap my brain around the evidence for accelerating expansion of the universe from type 1a supernovae. From what I understand, it was first realized that the universe was expanding at an increasing rate from discrepancies between the calculated distances to type 1a supernovae using...
12. ### What is the rate of gas expansion in a vacuum?

Say that there's a large metal box with nothing but a vacuum inside of it, except for a small bag of compressed gas at the center. If the bag were to suddenly pop, is there a specific rate that this gas would accelerate when expanding to meet the space of the container? I think that it might...
13. ### Solving expansion rate for a variant of the Friedmann equation

Homework Statement For the equation H^2 = \frac{8 \pi G \rho_m}{3} + \frac{H}{r_c} how do I find the value of H for scale factor a \rightarrow \infty , and show that H acts as though dominated by \Lambda (cosmological constant) ? Homework Equations \rho_m \propto \frac{1}{a^3} H > 0...
14. ### A question relating to expansion rate of the Universe

1. Forgive me for this novice question, but can variation in the expansion rate of the universe, be partially explained by an increasing number of stars turning mass into energy, hence reducing gravitational attraction between galaxies, and at the same time applying radiation pressure (a small...
15. ### Hot gas expansion rate into outer space

Good Morning Sirs, it seems to be surprisingly hard to get the numbers of a mystery: How fast expand hot rocket exhaust gases into empty space? Of course aside from its exit velocity! Does the expansion interfere with the impulse direction? I.e. is the impulse omnidirectional effective...
16. ### Expansion Rate at the Big Bang: Uncovering the Role of Dark Matter

If dark matter is accelerating the expansion of the universe, then how fast did the universe start expanding at the point of the Big Bang ? The pre-Standard Candle model of the Big Bang held that the expansion rate had always been declining and by backward interpolation, must have been very...
17. ### Highest expansion rate during inflation.

What is the highest expansion rate during inflation?
18. ### Expansion rate of Carbon Fiber vs Steel

I am a lisc. Auto body tech, and I have a customer who wants a Carbon Fiber roof on a Volkwagen bug, I can fabricate a inner frame, and bonding will not be an issue, (according to paint rep) The hard part is I want to do a flush seem and have paint blend into carbon fiber. I will "butt" match...
19. ### Is the expansion rate of the universe slowing?

In a reply to a correspondents question, it was stated that the expansion rate of the universe is slowing. This would seem in direct contrast to the accelerating rate of expansion that we have been hearing of since '98. An invisible form of repellent energy that is able to overcome gravity...
20. ### Expansion rate of the universe

Most articles sate that basically the further away an object is, the faster it is moving away from us therefore the universe is expanding faster which leads to dark energy to explain the increasing accelaration But as we see distant objects as they were in the past due to the finite speed of...
21. ### How Fast Does Nitrogen Expand to Power Piston Arms?

i'm trying to figure out the expansion rate of nitrogen at any given psi in room temperature. roughly in fps. trying to calculate how fast we can move a piston arm to get maximum velocities
22. ### Redshift, Distance & Expansion rate question

I'm a bit confused about redshift and the apparent increase in acceleration. If I understood it correctly redshift is caused by the expansion of the universe (space itself). What I don't understand though, if galaxies further away have a higher increase in redshift vs distance than galaxies...
23. ### Void expansion rate and cosmic acceleration.

A proliferation of very large voids have been observed recently, at a scale of 250-350 Mpc. Voids are believed to have average densities about 10% of the cosmic average. Voids are conservatively believed to comprise at least 60% of the volume of the observable universe, and perhaps more than...
24. ### Why does higher density of the early universe result in a faster expansion rate?

I heard from a TV program that higher density of the early universe resulted in a faster expansion rate, and the lower density of the present universe has a lower expansion rate. Could anyone please expalin to me why? Thanks =)
25. ### Expansion rate of the universe

I am not an expert on this matter but it got really interested in the physics of the expanding universe, I believe that the universe is expanding. My question is how could science know if this expansion rate is increasing or decreasing, and how can science ever measure such a rate. Also I would...
26. ### Understanding the Impact of Increased Universal Expansion Rate

Hello all... Hope you'll allow a complete novice to sneak in for a moment or two with a couple of questions: (1)Disregarding any preferential viewpoint, like Earth, and at any instant, is universal expansion velocity the same? (2)In what way(s) does the recently discovered increased...