astronomy

Weber bar

Weber bar is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Weber bar rather than just read about it. In short: A Weber bar is a type of resonant mass gravitational wave detector designed to detect gravitational waves, devised and constructed by physicist Joseph Weber at the University of Maryland. Multiple of these devices were made, both of consisting of aluminium cylinders and stated to be 1.5 (5ft) meters in length, 0.6m (2ft) and 0.2m (8") in diameter, antennae for detecting gravitational waves.

Key takeaways

Weber bar belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Weber bar to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Weber bar from memory before moving on to harder problems.

Reference excerpt

A Weber bar is a type of resonant mass gravitational wave detector designed to detect gravitational waves, devised and constructed by physicist Joseph Weber at the University of Maryland. Multiple of these devices were made, both of consisting of aluminium cylinders and stated to be 1.5 (5ft) meters in length, 0.6m (2ft) and 0.2m (8") in diameter, antennae for detecting gravitational waves. There is a third with a 1220 hertz resonance without stated length parameters. A resonant mass gravitational wave detector in the style of the Weber bar is on display at Glasgow University.

Mechanism These massive aluminium cylinders vibrated at a resonance frequency of 1660 or 1220 hertz and were designed to be set in motion by gravitational waves predicted by the general theory of relativity. Because gravitational waves were predicted to be very weak, the size of the bars and were designed to be large to compensate since these waves cause a percentage change in length. These tiny displacements are then read out by piezoelectric sensors which had to be very sensitive, capable of detecting a change in the cylinders' lengths by about 10−16 meters. These bars were situated in a vacuum chamber, hung on acoustic filters which appear to be made up of masses on springs, with further isolation via rubber pads situated between steel blocks.

History Around 1968, Weber collected what he concluded to be "good evidence" of the theorized phenomenon; additionally writing newspaper articles stating as such. However, his experiments were duplicated many times, always with a null result. Such experiments conducted by Joseph Weber were very controversial, and his positive results with the apparatus, in particular his claim to have detected gravitational waves from SN1987A in 1987, were widely discredited. Criticisms of the study have focused on Weber's data analysis and his incomplete definitions of what strength vibration would signify a passing gravitational wave. Weber's first "Gravitational Wave Antenna" was on display in the Smithsonian Institution as part of "Einstein: a Centenary Exhibit" from March 1979 to March 1980. A second is on display at the LIGO Hanford Observatory.

Weber Memorial Garden was dedicated 2019 at the University of Maryland, where Weber was a faculty member. The garden contains eight of the cores of Weber's bar detectors.

References

Further reading Gretz, Darrell J. (2018), "Early History of Gravitational Wave Astronomy: The Weber Bar Antenna Development", History of Physics Newsletter, 13 (6): 1–16 Weber, J. (1967), "Gravitational radiation", Physical Review Letters, 18 (13): 498–501, Bibcode:1967PhRvL..18..498W, doi:10.1103/PhysRevLett.18.498 Weber, J. (1968), "Gravitational-wave-detector events", Physical Review Letters, 20 (23): 1307–1308, Bibcode:1968PhRvL..20.1307W, doi:10.1103/PhysRevLett.20.1307 Weber, J. (1969), "Evidence for discovery of gravitational radiation", Physical Review Letters, 22 (24): 1320–1324, Bibcode:1969PhRvL..22.1320W, doi:10.1103/PhysRevLett.22.1320 Weber, Joseph. How I discovered Gravitational Waves, Popular Science, Bonnier Corporation, May 1972, Vol. 200, No. 5, pp. 106–107 & 190–192, ISSN 0161-7370.

Illustrations

Worked examples

Example 1 — a first encounter with Weber bar

Start with the simplest possible case. Write down what Weber bar claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Weber bar before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Weber bar ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Weber bar

In research: Weber bar appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Weber bar in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Weber bar is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomy in the United States, Gravitational-wave telescopes, so understanding it makes those chapters shorter.
In everyday life: Look for Weber bar outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Weber bar” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Weber bar in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Weber bar means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Weber bar out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Weber bar in simple terms?

Why does Weber bar matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Weber bar?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Weber bar.