Expansion of the Universe, cop this

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Discussion Overview

The discussion centers around the concept of the expansion of the universe and its implications, particularly in relation to mass and gravity as objects approach the speed of light. Participants explore various interpretations of relativistic mass, gravitational effects, and misconceptions in cosmology.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant proposes a theory that the accelerating expansion of the universe leads to an increase in mass, which would subsequently slow the expansion due to increased gravity.
  • Another participant argues that the expansion of the universe involves space itself expanding, not objects moving through space, thus negating the idea of relativistic mass increase in this context.
  • A participant suggests that developing personal theories may be premature without a solid understanding of established concepts in cosmology.
  • There is a discussion about whether objects gain mass as they approach near-light speed, with some affirming that relativistic mass increases with speed, while others clarify that mass in an object's own reference frame does not change.
  • Concerns are raised about the implications of mass increase, with one participant questioning whether objects approaching light speed would collapse into black holes, which another participant refutes by stating that extreme densities are required for black hole formation.
  • Participants discuss the concept of resistance to acceleration at high speeds, with references to how relativity affects perceived mass and weight from different frames of reference.

Areas of Agreement / Disagreement

Participants express differing views on the implications of relativistic mass and the nature of gravitational effects in the context of the universe's expansion. No consensus is reached regarding the validity of the initial theory or the relationship between mass and black hole formation.

Contextual Notes

Some statements reflect common misconceptions about cosmology and relativity, and there are unresolved questions about the nature of mass and gravity in accelerating frames of reference.

Ryan Lucas
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Hi! I am doing year eleven physics and love it, I am a teachers pet and all. Anyway, I have this theroy with my physics teacher, we came up with it together its really cool. So anyway, the expansion of the universe is accelerating, "defying gravity". Anyway, let's assume that it keeps accellerating infinitely. Now eventually the expansion of the universe must reach near light speed right? now an object traveling at near light speed GAINS MASS, it weighs more. Now with a higher mass, it thus has more gravity, more gravity means that the accelerating expansion of the universe must slow, Ergo universal equilibrium!

Have you got any thoughts on my theory? Can you disprove it? Please do!
 
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Ryan Lucas said:
Have you got any thoughts on my theory? Can you disprove it? Please do!
If I'm understanding it correctly, it would appear to be another case of misunderstanding the expansion of the universe. The things in the universe are not moving relative to the space they're in; the space itself is expanding. Therefore, no relativistic mass increase.
 
Ryan Lucas said:
Hi! I am doing year eleven physics and love it, I am a teachers pet and all. Anyway, I have this theroy with my physics teacher, we came up with it together its really cool.
While your enthusiasm is admirable, perhaps it's a bit premature to be developing your own theory. :wink:

I'll move this to the General Astronomy and Cosmology section, where experts aplenty will inform and delight you!
 
An accelerating body does not have more gravity or mass. What you are talking about is relativistic mass, and that does not add to the weight of an object. Consider an object falling to earth. As it gets closer there is acceleration due to gravity, so the object speeds up. It does not change its weight as it is falling. When it hits the ground it may leave a deep impression, deeper than it would have if it was dropped from less of a height. This is because of the objects inertia and not its weight which remains constant.
 
Welcome to Physics Forums, Ryan_Lucas!

As Danger already mentioned, part of your idea is one of the most common misconceptions about cosmology (and GR). There's a recent issue of Scientific American with an article by Lineweaver (he of UNSW) on this (and other) misconceptions. IIRC, there's a link to an online version of this article in another thread here in GA&C. If not, I'm sure a quick google will find it. If you're interested, here's a more technical paper by Lineweaver and his colleague, Tamara Davis
 
Mmmm, thanks for your responses, they really helped. By the way, am i right that when they reach NEAR LIGHT velocity, an object will gain mass? This is shown by einstein's famous formula?
 
Ryan Lucas said:
am i right that when they reach NEAR LIGHT velocity, an object will gain mass? This is shown by einstein's famous formula?
An object gains relativistic mass with every increase of speed. (And keep in mind that velocity is a vector, as opposed to speed which is a scalar measurement. ie: velocity requires a direction as well as a speed. This is why something veering off on a tangent to its original course undergoes a change of velocity even if its speed remains constant.) You have the right basic idea, but serious refinement of it is necessary.
 
If you were co-accelerating with the body in question, you would both swear neither of you gained a pound.
 
Chronos said:
If you were co-accelerating with the body in question, you would both swear neither of you gained a pound.
I am so tempted to make a Jenny Craig joke here, that I think I shall head down to GD before I say something embarrassing.
 
  • #10
This is cool man

Ryan Lucas said:
Mmmm, thanks for your responses, they really helped. By the way, am i right that when they reach NEAR LIGHT velocity, an object will gain mass? This is shown by einstein's famous formula?

If what U r saying is right then all the objects apporaching speed of light must collapse into BlackHoles, Wow I never thought of that before. All this is vrey enlightening.
 
  • #11
no, that is incorrect. the mass of the object in it's own reference frame does not change, hence it doesn't collapse into a black hole.
 
  • #12
O yaa

matt.o said:
no, that is incorrect. the mass of the object in it's own reference frame does not change, hence it doesn't collapse into a black hole.

Then where is the resistance to the acceleration coming form as we approach highere speeds ? Or is it an problem limited to the particle accelerators only.
 
  • #13
actually, I think relativistic mass may contribute to a gravitational field, I am no expert here! nevertheless, the mass has to be confined within a region such that the density must be high enough to form a black hole. mass alone does not cause a body to collapse into a black hole, extreme densities are needed.
 
  • #14
Anomalous said:
Then where is the resistance to the acceleration coming form as we approach highere speeds ?
That's where the 'relative' part of 'Relativity' comes in. To itself, the object undergoes no change. Relative to an outside observer, it gains mass, shortens, and has its time slowed. If, for instance, the Earth were to speed up in its orbit, taking you with it, you would still weigh the same on your bathroom scale even though you are moving faster. Someone on Mars would think, "Jeez, that guy's getting heavy!"
 

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