- #1
Aki
- 83
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Is there anything such as antigravity?
Is there anything such as antigravity?
- Thread starter Aki
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Discussion Overview
The discussion centers around the concept of antigravity, exploring various interpretations and implications within the realms of physics, particularly in relation to gravity, special relativity, and exotic matter. Participants examine both theoretical and conceptual aspects, including buoyancy, antimatter, and cosmological constants.
Discussion Character
- Exploratory
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- Some participants suggest that buoyancy could be considered a form of antigravity.
- Others argue that there is no experimental evidence supporting the existence of mass that can repel other mass, as seen in the analogy of electrical charges.
- A participant mentions that while antimatter might imply antigravity, current observations indicate that antimatter behaves consistently with gravity, falling down rather than up.
- Special relativity is proposed to predict a form of antigravity through a negative pressure equation of state in the vacuum, leading to large-scale repulsion when a positive cosmological constant is present.
- There is a correction regarding the mention of special relativity instead of general relativity in the context of antigravity predictions.
- Questions arise about the nature of negative pressure and its implications in the context of vacuum and exotic matter.
- Participants express confusion regarding the concept of negative pressure and seek further clarification.
- A participant asks for clarification on the term "redshift" in relation to a cosmology tutorial, indicating a desire for deeper understanding.
Areas of Agreement / Disagreement
Participants do not reach a consensus on the existence or nature of antigravity, with multiple competing views and interpretations presented throughout the discussion.
Contextual Notes
Some concepts discussed, such as negative pressure and the behavior of antimatter, remain complex and are not fully resolved within the conversation. The discussion also highlights the dependence on definitions and interpretations of terms like "antigravity."
- #2
Nereid
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Welcome to Physics Forums Aki!
It rather depends on what you mean by 'anti-gravity'.
In one sense, bouyancy could be thought of as anti-gravity.
If you are thinking of an analogy with electrical charges (like charges repel, unlike charge attract), or a bar magnet, then the answer is no; there is no experimental or observational result which suggests that there are forms of mass which can repel each other.
You might think that atoms of anti-matter would show anti-gravity? (for example, anti-hydrogen, made of an anti-proton and a positron, would 'fall up' in a vacuum tube here on Earth) Well, no; although this hasn't been observed yet (anti-hydrogen is very difficult to make!), the limited results on the gravitational effect of anti-matter are consistent with the theory - anti-matter 'falls down'.
It rather depends on what you mean by 'anti-gravity'.
In one sense, bouyancy could be thought of as anti-gravity.
If you are thinking of an analogy with electrical charges (like charges repel, unlike charge attract), or a bar magnet, then the answer is no; there is no experimental or observational result which suggests that there are forms of mass which can repel each other.
You might think that atoms of anti-matter would show anti-gravity? (for example, anti-hydrogen, made of an anti-proton and a positron, would 'fall up' in a vacuum tube here on Earth) Well, no; although this hasn't been observed yet (anti-hydrogen is very difficult to make!), the limited results on the gravitational effect of anti-matter are consistent with the theory - anti-matter 'falls down'.
- #3
geometer
- 194
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Special Relativity predicts a kind of anti-gravity. Special Relativity requires that the vacuum have a negative pressure equation of state, given this, a positive cosmological constant will act to cause a large scale repulsion.
- #4
Gonzolo
geometer said:
I think you mean General Relativity.
- #5
geometer
- 194
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oops - yes!
- #6
Mk
- 2,040
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An exotic form of matter would, in the spaceitme-is-a-sheet analogy be on top of a hill instead of in a little hole. How is there negative pressure in a vacuum?
- #7
Aki
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geometer said:
what is negative pressure? I've always had trouble understanding it
- #8
Nereid
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You might find this page, from Ned Wright's cosmology tutorial, helpful. If, after reading it, you still have questions (I hope that you do!), please come back and ask.Aki said:
- #9
Aki
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Nereid said:You might find this page, from Ned Wright's cosmology tutorial, helpful. If, after reading it, you still have questions (I hope that you do!), please come back and ask.
thanks for ths site. Um...I already have a question on the first sentence; "Recently two different groups have measured the apparent brightness of supernovae with redshifts near z = 1." What is that "z"?
- #10
Nereid
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redshift; z = (observed wavelength - 'source' wavelength)/('source' wavelength).Aki said:
http://www.wordiq.com/definition/Redshift
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