Is there anything such as antigravity?

[Aki]

Is there anything such as antigravity?

 

[Nereid]

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'.

 

[geometer]

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.

 

[Gonzolo]

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.

I think you mean General Relativity.

 

[geometer]

oops - yes!

 

[Mk]

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?

 

[Aki]

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.

what is negative pressure? I've always had trouble understanding it

 

[Nereid]

what is negative pressure? I've always had trouble understanding it

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]

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"?

 

[Nereid]

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"?

redshift; z = (observed wavelength - 'source' wavelength)/('source' wavelength).
http://www.wordiq.com/definition/Redshift